Helminthology PDF

PART TWO Cestodes: 62 - Taenia 63 - Diphyllobothrium Latum 67 - Hymenolepis Nana 68 - Echinococcus Granulosus 70 - Cestodes of Minor importance...

PART TWO Cestodes: 62 - Taenia 63 - Diphyllobothrium Latum 67 - Hymenolepis Nana 68 - Echinococcus Granulosus 70 - Cestodes of Minor importance 71 Trematodes: 72 -Schistosomiasis 73 Nematodes: 81 Intestinal: 83 - Ascaris Lumbricoides 83 - Ankylostoma duodenale & Necator Americanus 85 - Strongyloides Stercoralis 87 - Enterobius Vermicularis 89 - Trichuris Trichuria 90 - Trichinella Spiralis 91 Tissue: 93 - Wuchereria bancrofti. 94 - Brugia malayi. 96 - Onchocerca volvulus. 97 - Loa loa. 98 - Dracunculus 99 - Animal 100 61 Helminthology  Cestodes - Platyhelminthes (platy means flat; helminth means worm) are divided into two classes: Cestoda (tapeworms) and Trematoda (flukes). - Tapeworms consist of two main parts: a rounded head called a scolex and a flat body of multiple segments called proglottids. - The scolex has specialized means of attaching to the intestinal wall, namely, suckers, hooks, or sucking grooves. - The worm grows by adding new proglottids from its germinal center next to the scolex (the neck). - Each proglottid possesses a complete male & female reproductive system, hence cestodes are hermaphrodite. - In each segment there is a number of testes, a bilobed ovary & a convoluted uterus with a central stem & lateral branches. The number of these lateral branches is of a diagnostic importance. - The oldest proglottids at the distal end are gravid and produce many eggs, which are excreted in the feces and transmitted to various intermediate hosts such as cattle, pigs, and fish. - Humans usually acquire the infection when undercooked flesh containing the larvae is ingested. However, in two important human diseases, cysticercosis and hydatid disease, it is the eggs that are ingested and the resulting larvae cause the disease. - The eggs contain the embryo, which is called oncosphere, it possesses six hooks so it is hexa canth embryo. - There is no mouth or digestive system. Nutrients are directly absorbed through. The surface of the worm (no need for GIT => physiological adaptation). - Pathogenicity is either by passive obstruction or migration to unusual sites or by competition with the host for nutrients. - There are five medically important cestodes: - Taenia solium & Taenia saginata, Diphyllobothrium latum, Echinococcus granulosus & Hymenolepis nana. - Two cestodes of lesser importance are: Echinococcus multilocularis and Dipylidium caninum. - Praziquantel is effective against all flat worms. - Niclosamide is also effective. 62 Cestodes  Taenia  Taenia solium ( The pork tapeworm ) : o The adult form of T. solium causes taeniasis. T. solium larvae cause cysticercosis.  Important Properties : - T. solium can be identified by its scolex, which has four suckers and circle of hooks, and by its gravid proglottids, which have 5 to 10 primary uterine branches. The eggs appear the same microscopically as those of T. saginata and Echinococcus species.  Life cycle : - In taeniasis, the adult tapeworm is located in the human intestine. This occurs when humans are infected by eating raw or undercooked pork containing the larvae, called cysticerci. (A cysticercus consists of a pea-sized fluid-filled bladder with an invaginated scolex). - In the small intestine, the larvae attach to the gut wall and take about 3 months to grow into adult worms measuring up to 5 m. The number of proglottids is 800-1000. - The gravid terminal proglottids containing many eggs detach daily, are passed in the feces, and are accidentally eaten by pigs. Note that pigs are infected by the worm eggs; therefore, it is the larvae (cysticerci) that are found in the pig. - A six-hooked embryo (oncosphere) emerges from each egg in the pig's intestine. The embryos burrow into a blood vessel and are carried to skeletal muscle. They develop into cysticerci in the muscle, where they remain until eaten by a human. 63 Cestodes  - Humans are the definitive hosts, and pigs are the intermediate hosts. - In cysticercosis, a more dangerous sequence occurs when a person ingests the worm eggs in food or water that has been contaminated with human feces. - Note that in cysticercosis, humans are infected by eggs excreted in human feces, not by ingesting undercooked pork. Also pigs do not have the adult worm in their intestine, so they are not the source of the eggs that cause human cysticercosis. - The eggs hatch in the small intestine, and the oncospheres burrow through the wall into a blood vessel. They can disseminate too many organs, especially the eyes and brain, where they encyst to form cysticerci. Each cysticercus contains a larva.  Pathogenesis & Epidemiology : - The adult tapeworm attached to the intestinal wall causes little damage. - The cysticerci, on the other hand, can become very large, especially in the brain, where they manifest as a space-occupying lesion. - Living cysticerci do not cause inflammation, but when they die they can release substances that provoke an inflammatory response. Eventually, the cysticerci calcify. - The epidemiology of taeniasis and cysticercosis is related to the access of pigs to human feces and to consumption of raw or undercooked pork. The disease occurs worldwide but is endemic in areas of Asia, South America, and Eastern Europe.  Clinical Findings : - Most patients with adult tapeworms are asymptomatic, but anorexia and diarrhea can occur. Some may notice proglottids in the stools. - Cysticercosis in the brain causes headache, vomiting, and seizures. Cysticercosis in the eyes can appear as uveitis or retinitis, or the larvae can be visualized floating in the vitreous. - Subcutaneous nodules containing cysticerci commonly occur (they appear as spindle shaped calcified material in the X-ray). Diagnosed by Histopathology.  Laboratory Diagnosis : - Identification of T. solium consists of finding gravid proglottids with 5 to 10 primary uterine branches in the stools. In contrast, T. saginata proglottids have 15 to 20 primary uterine branches. Eggs are found in the stools less often than are proglottids. - Diagnosis of cysticercosis depends on demonstrating the presence of the cyst in tissue, usually by surgical removal or CT scan or MRI. Histopathology for subcutaneous nodules. Radiology for presence of calcified material. - Serologic tests, e.g., ELISA, that detect antibodies to T. solium antigens are available, but they may be negative in neurocysticercosis. 64 Cestodes   Treatment : - The treatment of choice for the intestinal worms is Praziquantel. - The treatment for cysticercosis is either Praziquantel or albendazole, but surgical excision may be necessary.  Prevention : - Prevention of taeniasis involves cooking pork adequately and disposing waste properly so that pigs cannot ingest human feces. - Prevention of cysticercosis consists of treatment of patients to prevent autoinfection plus observation of proper hygiene, including handwashing, to prevent contamination of food with the eggs.  Taenia saginata ( The beef tapeworm ) : - T. saginata causes taeniasis. - T. saginata larvae do not cause cysticercosis.  Important Properties - T. saginata has a scolex with four suckers but, in contrast to T. solium, no hooklets. Its gravid proglottids have 15 to 25 primary uterine branches, in contrast to T. solium proglottids, which have 5 to 10. - The eggs are morphologically indistinguishable from those of T. solium (rounded with a thick shell which is radically striated & contains the hexacant embryo) except that T. solium eggs have 4-6 hooklets.  Life cycle : - Humans are infected by eating raw or undercooked beef containing larvae (cysticerci). - In the small intestine, the larvae attach to the gut wall and take about 3 months to grow into adult worms measuring up to 10 m. The number of proglottids may reach 1000-2000. - The gravid proglottids detach, are passed in the feces, and are eaten by cattle. - The embryos (oncospheres) emerge from the eggs in the cow's intestine and burrow into a blood vessel, where they are carried to skeletal muscle. In the muscle, they develop into cysticerci (cysticercus bovis). - This is a fluid-filled bladder which contains an inverted or invaginated scolex, and it is visible to the naked eye. It gives the meat a measly appearance (meat with white spots). - The cycle is completed when the cysticerci are ingested. Humans are the definitive hosts and cattle the intermediate hosts. - Unlike T. solium, T. saginata does not cause cysticercosis in humans. 65 Cestodes   Pathogenesis & Epidemiology : - Little damage results from the presence of the adult worm in the small intestine. - The epidemiology of taeniasis caused by T.Saginata is related to the access of cattle to human feces and to the consumption of raw or undercooked beef. - The disease occurs worldwide but is endemic in Africa, South America, and Eastern Europe.  Clinical Findings :  In spite of its large size, the worm is well tolerated by the host and it is usually a single adult worm (multiple worms are rare).  Most patients with adult tapeworms are asymptomatic.  Symptomatic infection includes : 1. Abdominal pain described as hunger pain (the pt. feels with pain when he is hungry). 2. Malaise. 3. Rarely can it cause intestinal obstruction. 4. When the Gravid proglottids pass through. The anus they may cause itching & great embracement.  Laboratory Diagnosis : - Identification of T. saginata consists of finding gravid proglottids with 15 to 20 uterine branches in the stools. - The uterus can also be stained by ingestion of dies like India ink thro. The genital pore & can be easily visualized. - Eggs are found in the stools less often than are the proglottids.  Treatment : - The treatment of choice is Praziquantel. - Niclosamide is also useful. - Purgatives may be given to facilitate expulsion of the worms & identification (Niclosamide kills the worm & the worm is expelled digested, so by Niclosamide we can't identify it, because if the head & neck of the worm are not expelled the worm will develop again in 3 months).  Prevention : - Prevention involves cooking beef adequately and disposing waste properly so that cattle cannot consume human feces. - 66 Cestodes  Diphyllobothrium latum  Diphyllobothrium latum, the fish tapeworm, causes diphyllobothriasis.  Important Properties : - In contrast to the other cestodes, which have suckers, the scolex of D. latum has two elongated sucking grooves by which the worm attaches to the intestinal wall (bothria). The scolex has no hooks, unlike T. solium and Echinococcus. - The proglottids are wider than they are long, and the gravid uterus is in the form of a rosette. Unlike other tapeworm eggs, which are round, D. latum eggs are oval and have a lidlike opening (operculum) at one end. - D. latum is the longest of the tapeworms, measuring up to 13 m.  Life cycle : - Humans are infected by ingesting raw or undercooked fish containing larvae (called plerocercoid or sparganum larvae). - In the small intestine, the larvae attach to the gut wall and develop into adult worms. - Gravid proglottids release fertilized eggs through a genital pore, and the eggs are then passed in the stools. The immature eggs must be deposited in fresh water for the life cycle to continue. - The embryos emerge from the eggs (ciliated embryo => Coracidium) and are eaten by tiny copepod crustacea (first intermediate hosts). There, the embryos differentiate and form procercoid larvae in the body cavity. - When the copepod is eaten by freshwater fish, e.g., pike, trout, and perch, the larvae differentiate into plerocercoids in the muscle of the fish (second intermediate host). - The cycle is completed when raw or undercooked fish is eaten by humans (definitive hosts).  Pathogenesis & Epidemiology : - Infection by D. latum causes little damage in the small intestine. - In some individuals, megaloblastic anemia occurs as a result of vitamin B12 deficiency caused by preferential uptake of the vitamin by the worm. - The epidemiology of D. latum infection is related to the ingestion of raw or inadequately cooked fish and to contamination of bodies of fresh water with human feces. - The disease is found worldwide but is endemic in areas where eating raw fish is the custom, such as Scandinavia, northern Russia, Japan, Canada, and certain north- central states of the United States. 67 Cestodes   Clinical Findings : - Most patients are asymptomatic, but abdominal discomfort and diarrhea can occur.  Laboratory Diagnosis : - Diagnosis depends on finding the typical eggs, i.e., oval, yellow-brown eggs with an operculum at one end, in the stools. - There is no serologic test.  Treatment : - The treatment of choice is Praziquantel (or) Niclosamide + vitamin B12 supplement.  Prevention : - Prevention involves adequate cooking of fish and proper disposal of human feces. Hymenolepis nana - H. nana (dwarf tapeworm) is very common, it is one of the most frequently found tapeworms in Sudan. - It is only 3 to 5 cm long, the scolex possesses 4 suckers & one row of hooks. It is different from other tapeworms because its eggs are directly infectious for humans, i.e., ingested eggs can develop into adult worms without an intermediate host. - Within the duodenum, the eggs hatch and differentiate into cysticercoid larvae (in intestinal villi) and then into adult worms. - Gravid proglottids detach, disintegrate, and release fertilized eggs. The eggs either pass in the stool or can reinfect the small intestine (autoinfection). - In contrast to infection by other tapeworms, where only one adult worm is present, many H. nana worms (sometimes hundreds) are found. - Infection causes little damage, and most patients are asymptomatic. Heavy infection may cause diarrhoea, abdominal pain, headache, dizziness & nonspecific symptoms. Eosinophilia is common. - The organism is found worldwide, commonly in the tropics. In the United States, it is most prevalent in the southeastern states, usually in children. - Diagnosis is based on finding eggs in stools. The characteristic feature of H. nana eggs is the 8 to 10 polar filaments lying between the membrane of the six-hooked larva and the outer shell. - The treatment is praziquantel or Niclosamide. - Prevention consists of good personal hygiene and avoidance of fecal contamination of food and water.  Note: intestinal autoinfection is seen in: H.nana, Strongyloides, and Cryptosporidium & Enterobius. 68 Cestodes  Echinococcus granulosus - Echinococcus granulosus (dog tapeworm) causes echinococcosis. - The larva of E. granulosus causes unilocular hydatid cyst disease. - Multilocular hydatid disease is caused by E. multilocularis, which is a minor pathogen.  Important Properties : - E. granulosus is composed of a scolex and only three proglottids (the first is immature, the second is mature & the third is the gravid segment), making it one of the smallest tapeworms (3-6 mm in length). - The scolex has a circle of hooks and four suckers similar to T. solium. - Dogs are the most important definitive hosts. The intermediate hosts are usually sheep. Humans are almost always dead-end intermediate hosts. So it is a zoonotic disease.  Life cycle : - In the typical life cycle, worms in the dog's intestine liberate thousands of eggs, which are ingested by sheep (or humans). - The oncosphere embryos emerge in the small intestine and migrate primarily to the liver but also to the lungs, bones, and brain. - The embryos develop into large fluid-filled hydatid cysts. If we examined the cyst we will identify 3 layers: 1. an outer fibrous layer formed by the host, 2. Laminated layer formed by the parasite (non-nucleated layer) and 3. Inner nucleated germinal layer which generates many protoscoleces within "broad capsules." - The life cycle is completed when the entrails (e.g., liver containing hydatid cysts) of slaughtered sheep are eaten by dogs.  Pathogenesis & Epidemiology : - E. granulosus usually forms one large fluid-filled cyst (unilocular) that contains thousands of individual scoleces as well as many daughter cysts within the large cyst. Free broad capsules & free protoscoleces lying at the bottom of the large cyst are called "hydatid sand" => diagnostically important. - The cyst acts as a space-occupying lesion, putting pressure on adjacent tissue. The outer layer of the cyst is thick, fibrous tissue produced by the host. The cyst fluid contains parasite antigens, which can sensitize the host. Later, if the cyst ruptures spontaneously or during trauma or surgical removal, life-threatening anaphylaxis can occur. - Rupture of a cyst can also spread protoscoleces widely. - The disease is found primarily in shepherds living in the Mediterranean region, the Middle East, and Australia. In the United States, the western states report the largest number of cases. 69 Cestodes   Clinical Findings : - The cyst size may reach up to 20 cm2 and the fate of the Hydatid cyst is unpredictable. Some grow until rupture, some of them stop growing & regress in size while other cysts are sterile from the beginning with no protoscoleces. - 70% of Hydatid cysts develop in the liver, 20% develops in the lungs, 10% develop in other sites e.g. brain. - The clinical presentation depends on: the mechanical effect of the cyst, allergic reaction to cyst components & complications due to rupture of the cyst. 1. Mechanical effect of the cyst : - Cyst may press on adjacent organs: Liver => painful enlargement (common presentation). Bile ducts or on major blood vessels. Lungs => Cysts in the lungs can erode into a bronchus causing cough, breathlessness, hemoptysis and it may cause lung collapse if it compresses a main bronchus. Brain => cerebral cysts can cause headache and focal neurologic signs (SOL). 2. Allergic reaction to cyst components : - Hydatid fluid may escape to the circulation and it can cause fatal anaphylactic shock, if Hydatid fluid is in small amount it only cause’s urticaria. 3. Complications due to rupture of the cyst : - Anaphylaxis, dissemination of the cyst to other organs (occurs by seeding of viable germinal epithelium) & secondary bacterial infection.  D.D of a Hydatid cyst in the liver : 1. Pyogenic liver abscess. 2. Amebic liver abscess (ALA). 3. Necrotic hepatoma.  D.D of unilateral proptosis : 1. Orbital Tumor (most common cause). 2. Sinus Aspergillosis. 3. Hydatid cyst.  Laboratory Diagnosis : - Diagnosis is based on microscopic examination demonstrating the presence of broad capsules containing multiple protoscoleces or Histopathology (detection of the three layers). Aspiration for diagnostic purposes should not be done when the cyst is inside the body. - Serologic tests, e.g., the indirect hemagglutination test, ELISA, CIEP, and CFT (may give positive results in pts. with lung cancer). - Cansoni skin test (Asten test): inject 0.1 ml sterile Hydatid fluid intradermally, immediate reaction in 20 minutes means positive result. Unreliable test because it may remain positive long after the cyst has been removed. - Antigen detection is the best way to diagnose Hydatid cyst, an important antigen is (arc 5), and it is detected by ELISA. 70 Cestodes   Treatment : - Treatment involves Albendazole with or without surgical removal of the cyst. It causes cyst regression & prevents recurrence. - Extreme care must be exercised to prevent release of the protoscoleces during surgery. - A protoscolicidal agent, e.g., hypertonic saline, should be injected into the cyst to kill the organisms and prevent accidental dissemination. other agents include : Cetrimide , H2O2 , Ethanol , Silver nitrate , Formaline ( may cause biliary damage => not recommended ).  Prevention : - Prevention of human disease involves not feeding the entrails of slaughtered sheep to dogs. Cestodes of minor importance  Echinococcus multilocularis : - Many of the features of this organism are the same as those of E. granulosus, but the definitive hosts are mainly foxes and the intermediate hosts are various rodents. - Humans are infected by accidental ingestion of food contaminated with fox feces. - The disease occurs primarily in hunters and trappers and is endemic in northern Europe, Siberia, and the western provinces of Canada. In the United States, it occurs in North and South Dakota, Minnesota, and Alaska. - Within the human liver, the larvae form multiloculated cysts with few protoscoleces. - No outer fibrous capsule forms, so the cysts continue to proliferate, producing a honeycomb effect of hundreds of small vesicles. - The clinical picture usually involves jaundice and weight loss. - The prognosis is poor. Albendazole treatment may be successful in some cases. Surgical removal may be feasible.  Dipylidium caninum : - D. caninum is the most common tapeworm of dogs and cats. - It occasionally infects humans, usually young children, while playing with their pets. - Human infection occurs when dog or cat fleas carrying cysticerci are ingested. The cysticerci develop into adult tapeworms in the small intestine. - Most human infections are asymptomatic, but diarrhea and pruritus ani can occur. - The diagnosis in animals and humans is made by observing the typical "barrel- shaped" proglottids in the stool or diapers. - Niclosamide is the drug of choice.  D.D of perianal pruritis: T. saginata, Diphylidium caninum, Enterobius vermicularis, Dientamoeba Fragilis, Taenia cruris (dermatophyte infection). (2 Di, 2 T & E). 71 Cestodes  Trematodes (flukes)  Trematoda (flukes) and Cestoda (tapeworms) are the two large classes of parasites in the phylum Platyhelminthes.  Characteristics of Trematodes : 1. They are flat dorso-ventrally and so are called flat helminths. 2. They are bilaterally symmetrical. 3. They have a digestive system, composed of a mouth, esophagus & two blind ended cecum. 4. They are true hermaphrodites except for Schistosoma species. 5. They have suckers which are muscular organs used for attachment. 6. They produce eggs & they are mostly parasitic.  The most important trematodes are Schistosoma species (blood flukes), liver flukes, intestinal flukes and Paragonimus westermani (lung fluke).  Schistosoma’s have by far the greatest impact in terms of the number of people infected, morbidity, and mortality.  The life cycle of the medically important trematodes involves a sexual cycle in humans (definitive host) and asexual reproduction in freshwater snails (intermediate hosts).  Transmission to humans takes place either via penetration of the skin by the free- swimming cercariae of the schistosomes or via ingestion of cysts in undercooked (raw) fish or crabs in Clonorchis and Paragonimus infection, respectively.  They are divided into : 1. Blood flukes: Schistosoma. 2. Intestinal flukes: Fasciolopsis buski, Heterophyes heterophyes & Metagonimus species. 3. Liver flukes: Fasciola hepatica, Fasciola gigantica & Clonorchis sinensis. 4. Lung flukes: Paragonimus species. 72 Trematodes  Blood flukes Schistosomiasis (Bilharziasis)  Schistosoma causes schistosomiasis. Schistosoma mansoni and Schistosoma japonicum as does Schistosoma mekongi affect the gastrointestinal tract, whereas Schistosoma hematobium affects the urinary tract.  In Sudan, the prevalence of schistosomiasis is more than 40% => El Jazeera, 25% in the White Nile.  From egg to adult worm.  Pathogenesis & Epidemiology : - Most of the pathologic findings are caused by the presence of eggs in the liver, spleen, or wall of the gut or bladder. - Eggs in the liver induce granulomas (Bilharziomas), which lead to fibrosis, hepatomegaly, and portal hypertension. 73 Trematodes  - The granulomas are formed in response to antigens secreted by the eggs. Hepatocytes are usually undamaged, and liver function tests remain normal. Portal hypertension leads to splenomegaly. - Sch. mansoni eggs damage the wall of the distal colon (inferior mesenteric venules), whereas Sch. japonicum eggs damage the walls of both the small and large intestines (superior and inferior mesenteric venules). - The damage is due both to digestion of tissue by proteolytic enzymes produced by the egg and to the host inflammatory response that forms granulomas in the venules. The eggs of S. haematobium in the wall of the bladder induce granulomas and fibrosis, which can lead to carcinoma of the bladder. - Schistosomes have evolved a remarkable process for evading the host defenses. - There is evidence that their surface becomes coated with host antigens, thereby limiting the ability of the immune system to recognize them as foreign. - The epidemiology of schistosomiasis depends on the presence of the specific freshwater snails that serve as intermediate hosts. - S. mansoni is found in Africa and Latin America (including Puerto Rico), whereas S. haematobium is found in Africa and the Middle East. S. japonicum is found only in Asia and is the only one for which domestic animals, e.g., water buffalo and pigs, act as important reservoirs. - More than 150 million people in the tropical areas of Africa, Asia, and Latin America are affected.  Characteristics of Sh.mansoni : - It is found in Africa, Asia, central & South America. - In Sudan, It is found mainly in irrigation projects because it needs a continuous supply of water. - The worms is leaf-like & it can live up to 5 years, but in some cases 37 years old worms occur. - Snails are of the genus Biomphalaria pferifferri.  Characteristics of Sh.jabonicum : - Found in Japan , China & Philippine , it causes more severe infection than Sh.mansoni : 1. It causes more morbidity because it produces more eggs than Sh.mansoni (3000 / day compared to 300 / day). 2. Eggs are smaller & so they can reach body organs easier => more eggs are carried to the CNS. 3. Complications appear earlier. 4. The disease is zoonotic, it can affect all domestic animals around people, so sources of infection are multiple. 5. The snail of Sh.jabonicum is amphibian I.e. it can live in water & earth unlike the others. - Snails are of the genus Oncomelania. 74 Trematodes   Characteristics of Sh.haematobium : - Eggs are excreted in urine. - Usually affects young age group, not found in those above 15-20 years old & the worm do not live long. - Eggs are yellow & contain the miracidium. - Snails are of the genus Bulinus truncates. - It is usually benign, but if it is taken by the inferior vena cava & affect the lung it may cause Cor-pulmonale. - Sh.haematobium is associated with Carcinoma of the bladder & formation of urinary calculi.  Clinical Findings : - Most patients are asymptomatic, but chronic infections may become symptomatic. - The acute stage (Katayama fever) , which begins shortly after cercarial penetration, consists of itching and dermatitis followed 2 to 3 weeks later by fever, chills, diarrhea, lymphadenopathy , and hepatosplenomegaly. High Eosinophilia is seen in response to the migrating larvae. - This stage usually resolves spontaneously. - The chronic stage can cause significant morbidity and mortality. - In patients with Sch. mansoni or S. japonicum infection, gastrointestinal hemorrhage, hepatomegaly, and massive splenomegaly can develop. Colonic polyposis with bloody diarrhea is associated mostly with Sh. mansoni. The most common cause of death is exsanguination from ruptured esophageal varices. - This is called (liver Schistosomiasis) which is manifested by:  Acute intestinal phase (dysentery) & Hepatosplenic phase (Hepatomegaly, Hypersplenism & pancytopenia). - Liver schistosomiasis is the second most common cause of esophageal varices. - [Extra:] Sch. japonicum can affect the CNS causing: cerebral granulomatous disease by ectopic eggs in the brain. And granulomatous lesions around ectopic eggs in the spinal cord (from both Sh. mansoni & Sh. japonicum) that may result in transverse myelitis with flaccid paralysis. - Patients infected with S. haematobium have terminal hematuria as their chief early complaint. Superimposed bacterial urinary tract infections occur frequently (burning micturition). - This is called (urinary Schistosomiasis) which may be complicated by fibrosis of the bladder & ureter leading to obstructive Uropathy and also Carcinoma of the bladder. - Pathologically the bladder is small with sandy patches that represents deposits of eggs in the mucous membrane. 75 Trematodes   Laboratory Diagnosis : - Clinically by history of endemicity, age, occupation & history of contact with water. - In the lab Diagnosis depends on finding the characteristic ova in the feces or urine. - The large lateral spine of Sch. mansoni and the rudimentary spine of S. japonicum are typical, as is the large terminal spine of Sch. haematobium. - Qualitative tests assess => presence or absence of eggs (e.g. rectal snip). Quantitative tests => number of eggs (for assessment of morbidity & for follow up) by Kato technique, Bell's technique & Teesatle amin's method. - Ultrasound is used to assess the degree of fibrosis in the liver. Endoscopy can be used for detection of esophageal varices. - Serologic tests are not useful. Moderate eosinophilia occurs. - Note: In 1% of cases, eggs of Sh.haematobium can be found in the stool beside the urine & can be found by examining rectal snip. Also in 1% of Sh.mansoni cases eggs can be found in urine.  Treatment : - Praziquantel is the treatment of choice for all three species. - Hepatic schistosomiasis can also be treated by Hyacanthone or Oxamniquine. - Urinary schistosomiasis can also be treated by Metrifonate. - Esophageal varices are treated by Sclerotherapy & shunt operations. - Judge the pt. response to treatment by examining stool & urine for eggs by performing the hatching test (add the eggs in fresh water to hatch).  Prevention : - Prevention involves proper disposal of human waste and eradication of the snail host when possible. Swimming in areas of endemic infection should be avoided.  Other species of Schistosoma :  Sh.mekongi & Sh.intercalatum causes intestinal Bilharziasis.  Sh.spurious causes "Swimmer's itch,” which consists of pruritic papules, is a frequent problem in many lakes in the world. The papules are an immunologic reaction to the presence in the skin of the cercariae of nonhuman schistosomes.  The pruritic papules appear within minutes to hours after exposure indicating that this is an immediate (IgE-mediated) hypersensitivity. Treated by Anti-histamines & Calamine lotions.  These nonhuman schistosomes are incapable of replicating in humans and do not cause disseminated disease. 76 Trematodes  Intestinal flukes  Fasciolopsis buski : - Fasciolopsis buski is an intestinal parasite of humans and pigs that is endemic to Asia and India. Pigs are the definitive host. - It is the largest fluke that infects man (known as Giant intestinal fluke). - Humans are infected by eating aquatic vegetation that carries the cysts. - After excysting in the small intestine, the parasites attach to the mucosa and differentiate into adults. Eggs are passed in the feces; on reaching fresh water, they differentiate into miracidia. - The ciliated miracidia penetrate snails and, after several stages (sporocyst => radiae) develop into cercariae that encyst on aquatic vegetation. - The cycle is completed when plants carrying the cysts are eaten. (Metacercaria of F.buski & F.hepatica are found in aquatic plants while metacercaria of other flukes are found in raw fish). - Pathologic findings are due to damage of the intestinal mucosa by the adult fluke. - Most infections are asymptomatic, but ulceration, abscess formation, and hemorrhage can occur with heavy infection. - Diagnosis is based on finding typical eggs in the feces (Large, oval & has small operculum (lid)). Adult worm is not usually seen in stool, it is seen only after the use of purgatives or anti-helminthic drugs. - Praziquantel is the treatment of choice. - Prevention consists of proper disposal of human sewage.  Heterophyes heterophyes : - Mainly a fluke of animals. Found China & Japan, in Africa it is found only in Egypt. - Eggs are very small. Infection is acquired by eating raw fish containing metacercaria. - Treated by Praziquantel.  Metagonimus species : - Found in Japan. Reservoir of infection are cats & dogs. - Eggs are very small. Infection is acquired by eating raw fish containing metacercaria. - Treated by Praziquantel. 77 Trematodes  Liver flukes  Fasciola hepatica :  Fasciola hepatica, the sheep liver fluke, causes disease primarily in sheep and other domestic animals in Latin America, Africa, Europe, and China.  Humans are infected by eating watercress (or other aquatic plants) contaminated by larvae (metacercariae) that excyst in the duodenum, penetrate the gut wall, and reach the liver, where they mature into adults (about 4 months after ingestion).  Hermaphroditic adults in the bile ducts produce eggs, which are excreted in the feces.  The eggs hatch in fresh water, and miracidia enter the snails. Miracidia develop into cercariae, which then encyst on aquatic vegetation.  Sheep and humans eat the plants, thus completing the life cycle. The flukes can live for many years in the host.  Symptoms are due primarily to the presence of the adult worm in the biliary tract.  In early infection, fever, right-upper-quadrant pain and hepatomegaly can occur, but most infections are asymptomatic.  Months or years later, obstructive jaundice can occur (Thickening of Bile ducts & liver enlargement). The Gallbladder can also be infected.  Halzoun is a painful pharyngitis caused by the presence of adult flukes on the posterior pharyngeal wall.  The adult flukes are acquired by eating raw sheep liver.  Diagnosis is made by identification of eggs in the feces => resembles those of F.buski (it poses an anterior conical projection). Eggs are found in feces only in chronic infection. Eggs can also be found in duodenum aspirate & in bile. There is no serologic test.  The drug of choice is triclabendazole. Adult flukes in the pharynx and larynx can be removed surgically.  Prevention involves not eating wild aquatic vegetables or raw sheep liver.  Marara syndrome ( Halzoun ) :  After taking raw liver containing F.hepatica worms, the worms sometimes stick to the upper respiratory passage causing upper respiratory tract obstruction.  Fasciola gigantica :  Cattle fluke (liver). Larger than F.hepatica. Can sometimes cause human infection. 78 Trematodes   Clonorchis:  Clonorchis sinensis causes clonorchiasis (Asian liver fluke infection).  Important Properties : - Humans are infected by eating raw or undercooked fish containing the encysted larvae (metacercariae). - After excystation in the duodenum, immature flukes enter the biliary ducts and differentiate into adults. - The hermaphroditic adults produce eggs, which are excreted in the feces. Upon reaching fresh water, the eggs are ingested by snails, which are the first intermediate hosts. - The eggs hatch within the gut and differentiate first into larvae (rediae) and then into many free-swimming cercariae. - Cercariae encyst under the scales of certain freshwater fish (second intermediate hosts), which are then eaten by humans.  Pathogenesis & Epidemiology : - In some infections, the inflammatory response can cause hyperplasia and fibrosis of the biliary tract, but often there are no lesions. - Clonorchiasis is endemic in China, Japan, Korea, and Indochina, where it affects about 20 million people.  Clinical Findings : - Most infections are asymptomatic. - In patients with a heavy worm burden, upper abdominal pain, anorexia, hepatomegaly, and eosinophilia can occur. - Complications include: Cholangitis , Cholangiocarcinoma , stones in the biliary tree & obstructive jaundice  Laboratory Diagnosis : - Diagnosis is made by finding the typical small, brownish, operculated eggs in the stool. Serologic tests are not useful.  Treatment : - Praziquantel is an effective drug.  Prevention : - Prevention centers on adequate cooking of fish and proper disposal of human waste. 79 Trematodes  Lung fluke (Paragonimus)  Paragonimus westermani, the lung fluke, causes paragonimiasis.  Important Properties : - Humans are infected by eating raw or undercooked crab meat (or crayfish) containing the encysted larvae (metacercariae). - After excystation in the small intestine, immature flukes penetrate the intestinal wall and migrate through the diaphragm into the lung parenchyma. They differentiate into hermaphroditic adults and produce eggs that enter the bronchioles and are coughed up or swallowed. - Eggs in either sputum or feces that reach fresh water hatch into miracidia, which enter snails (first intermediate hosts). There, they differentiate first into larvae (rediae) and then into many free-swimming cercariae. The cercariae infect and encyst in freshwater crabs (second intermediate hosts). - The cycle is completed when undercooked infected crabs are eaten by humans.  Pathogenesis & Epidemiology : - Within the lung, the worms exist in a fibrous capsule that communicates with a bronchiole. Secondary bacterial infection frequently occurs, resulting in bloody sputum. - Paragonimiasis is endemic in Asia and India.  Clinical Findings : - The main symptom is a chronic cough with bloody sputum, also there is fever & night sweating (The disease can resemble Tuberculosis). - Dyspnea, pleuritic chest pain, and recurrent attacks of bacterial pneumonia occur. - Flukes are found in cavities surrounded by inflammatory reactions. After treatment or death, healing occurs with scar formation, so in chest X-ray a cavity is seen (similar to Tb).  Laboratory Diagnosis : - Diagnosis is made by finding the typical operculated eggs in sputum or feces. Serologic tests are not useful.  Treatment : - Praziquantel is the treatment of choice.  Prevention : - Cooking crabs properly is the best method of prevention. 80 Trematodes  Nematodes - Nematodes (also known as Nemathelminthes) are round worms with a cylindrical body and a complete digestive tract, including a mouth and an anus. The body is covered with a noncellular, highly resistant coating called a cuticle. - Nematodes have separate sexes; the female is usually larger than the male. The male typically has a coiled tail. - The medically important nematodes can be divided into two categories according to their primary location in the body, namely, intestinal and tissue nematodes. - The 1. Intestinal nematodes (soil-transmitted worms) include Enterobius (pinworm), Trichuris (whipworm), Ascaris (giant roundworm), Necator and Ancylostoma (the two hookworms), Strongyloides (small roundworm), and Trichinella. - Enterobius, Trichuris, and Ascaris are transmitted by ingestion of eggs; the others are transmitted as larvae (penetration). - There are two larval forms: the first- and second-stage (rhabditiform) larvae are noninfectious, feeding forms; the third-stage (filariform) larvae are the infectious, nonfeeding forms. - As adults, these nematodes live within the human body, except for Strongyloides, which can also exist in the soil. - The larvae of Ascaris lumbricoides, Strongyloides stercoralis & Hook worms undergo migration thro. The right side of the heart & lung (Heart lung migration). o Lab diagnosis is based on : - Detection of Eggs in stool: for Ascaris, T.Trichuria & hook worms. - Detection of Eggs in perianal region: for E.Vermicularis. - Detection of Larvae in stool: for Strongyloides stercoralis. - Detection of Larvae in muscle: Trichinella. - The important (2.) Tissue nematodes Wuchereria, Onchocerca, and Loa are called the "filarial worms," because they produce motile embryos called microfilariae in blood and tissue fluids. - These organisms are transmitted from person to person by blood sucking mosquitoes or flies. - A fourth species is the guinea worm, Dracunculus, whose larvae inhabit tiny crustaceans (copepods) and are ingested in drinking water. [Extra] - The nematodes described above cause disease as a result of the presence of adult worms within the body. - In addition, several secies cannot mature to adults in human tissue, but their larvae can cause disease. 81 Nematodes - The most serious of these diseases is visceral larva migrans, caused primarily by the larvae of the dog ascarid, Toxocara canis. - Cutaneous larva migrans, caused mainly by the larvae of the dog and cat hookworm, Ancylostoma caninum, is less serious. - A third disease, anisakiasis, is caused by the ingestion of Anisakis larvae in raw seafood. - In infections caused by certain nematodes that migrate through tissue, e.g., Strongyloides, Trichinella, Ascaris, and the two hookworms Ancylostoma and Necator, a striking increase in the number of eosinophils (eosinophilia) occurs. - Eosinophils do not ingest the organisms; rather, they attach to the surface of the parasite via IgE and secrete cytotoxic enzymes contained within their eosinophilic granules. - Host defenses against helminths are stimulated by interleukins synthesized by the Th-2 subset of helper T cells; e.g., the production of IgE is increased by interleukin-4, and the number of eosinophils is increased by interleukin-5. - Cysteine proteases produced by the worms to facilitate their migration through tissue are the stimuli for IL-5 production. 82 Nematodes  Intestinal Nematodes Ascaris lumbricoides  Ascaris lumbricoides (earth worm) causes ascariasis.  Important Properties : - Humans are infected by ingesting worm eggs in food or water contaminated with human feces. - Children particularly affected heavily because they play in soil and contaminate their hands. - Eggs of Ascaris can survive in soil for years because the egg is surrounded by a highly resistant tough albuminous corrugated membrane, which resists dryness but is sensitive to exposure to sunlight. - The eggs hatch in the small intestine, and the larvae migrate through the gut wall into the bloodstream and then to the lungs. They enter the alveoli because they can't pass through. The small pulmonary capillaries.They pass up the bronchi and trachea by cilia and are swallowed. - Within the small intestine, they become adults. They live in the lumen, do not attach to the wall, and derive their sustenance from ingested food. - The adults are the largest intestinal nematodes, often growing to 25 cm or more (female is about 20-25 cm while male is about 15-30 cm). A. lumbricoides is known as the "giant roundworm." The oral cavity of both sexes is triangular in shape and is surrounded by 3 lips. The posterior end of the male is bended & it possesses 2 chitinous spicules. - Thousands of eggs are laid daily (200,000 / day), are passed in the feces, and differentiate into embryonated eggs in warm, moist soil. First eggs are not infective & contain non segmented embryo. - Ingestion of the embryonated eggs completes the cycle. -  Pathogenesis & Clinical Findings : - The major damage occurs during larval migration rather than from the presence of the adult worm in the intestine. - Ascaris Larvae are large & antigenic. Therefore during pulmonary migration they cause a lot of damage to the alveoli & allergic reactions. - When a large number of Larvae are migrating at the same time they cause a severe type of pneumonia called verminous pneumonia, which manifested clinically as fever, cough, dyspnea, wheezes, changing X-ray shadows and eosinophilia. These crystals are - Eosinophilia may be seen in the sputum. Disintegrated eosinophils may produce made up of crystals called Charcot’s crystals (in the sputum) which are also found in bronchial lysophospholipase, an enzyme from asthma. eosinophils - This condition is also called Loffler’s syndrome (chest symptoms & eosinophilia), which also occurs in hook worms & Strongyloides infection. Loffler’s syndrome resolves spontaneously after few days. 83 Nematodes  - D.D of Loeffler's syndrome: Tropical pulmonary eosinophilia (W.Bancrofti), allergic bronchopulmonary aspergillosis, Katayama Fever and some drugs (Mefloquine & Disodium cromoglycate). - The effect of adult worms depends on the worm load. Severe disease is associated with high worm load.  The main effects of the worms are mechanical effect and toxic & metabolic effects. 1. Mechanical effect : Volvulus involves twisting of the - The worm may obstruct the small intestine especially in children because of the intestine. small size of their intestines. So it can cause intestinal obstruction in form of Intussusception involves one part of volvulus & intussusception. the intestine sliding into another part. #‫مث‬ - The worm may obstruct the appendix causing acute appendicitis. ‫ايليم فوق دويدينم‬ - It may obstruct the biliary tree causing obstructive jaundice, or it may cause intrahepatic abscess if the worm dies in the liver. - It can obstruct the main pancreatic duct causing acute pancreatitis. Asphyxia is a medical - If a large number is passing through. The larynx, they can cause asphyxia. condition where the body or a part of the body is deprived of oxygen, leading 2. Toxic & metabolic effects : to a potential buildup of carbon dioxide. - Not well understood, but it is estimated that 15-50 worms lead to loss of 4 grams of proteins / day. - So heavy infection may cause malnutrition & growth retardation in children.  Clinical presentation : - Pts. may present with recurrent abdominal colics, nausea & vomiting. Pts. may Vomit worms or they may be coughed (the only worm that can be vomited or coughed), may be passed in the stool if there is diarrhoea of any cause. - Pts. may present with one of the complications: Acute appendicitis, asphyxia, malnutrition in children... etc....  Epidemiology : - Ascaris infection is very common, especially in the tropics; hundreds of millions of people are infected. In the United States, most cases occur in the southern states.  Laboratory Diagnosis : - Diagnosis is usually made microscopically by detecting eggs in the stools. The egg is oval with an irregular surface, yellow brown in color. Sometimes the eggs can be unfertilized if males are few, they are narrow, long and with dark brown pigment. - Occasionally, the patient sees adult worms in the stools, identified by size, shape & by the posterior end. - Eosinophilia is usually mild. 84 Nematodes   Treatment : - Pulmonary complications respond well to steroids. - Mebendazole (Vermox) is effective. - Piperazine salt, levamisole & Albendazole are also effective. - * Mebendazole & Albendazole are contraindicated in pregnant women.  Prevention : - Proper disposal of feces can prevent ascariasis. Ankylostoma duodenale & Necator americanus - Ancylostoma duodenale (Old World hookworm) and Necator americanus (New World hookworm) cause hookworm infection. - Called Hookworms because the head is sharply blended, forming a definitive hook. - The adult worms are similar but Necator is slightly smaller. The worms are reddish brown in color because they ingest blood and you can see a thread.  Important Properties : - Humans are infected when filariform larvae in moist soil penetrate the skin, usually of the feet or legs. They are carried by the blood to the lungs, migrate into the alveoli and up the bronchi and trachea, and then are swallowed (like Ascaris). - They develop into adults in the small intestine, attaching to the wall with either cutting plates (Necator) or teeth (Ancylostoma). They feed on blood from the capillaries of the intestinal villi. - Because they suck blood & proteins, they suck at regular intervals and from time to time they change the place of attachment. - Thousands of eggs per day are passed in the feces. Eggs develop first into noninfectious, feeding (rhabditiform) larvae and then into third-stage, infectious, nonfeeding (filariform) larvae, which penetrate the skin to complete the cycle. - Ancylostoma lays more eggs than Necator (2:1).  Pathogenesis & Clinical Findings : - The major damage is due to the loss of blood at the site of attachment in the small intestine & loss of proteins. - Ancylostoma (more) causes loss of about 0.5 ml / worm / day while Necator causes loss of about 0.03 ml / worm / day. - Blood is consumed by the worm and oozes from the site in response to an anticoagulant made by the worm. Weakness and pallor accompany the microcytic anemia caused by blood loss. 85 Nematodes  - Development of Iron deficiency anemia depends on: the worm load, worm type, Iron stores & presence of associated conditions like pregnancy & menstruation. - During larval migration thro. The lungs, Loeffler's syndrome arises with cough wheezes, X-ray shadows & Eosinophilia. This is less severe than Ascaris because the larva of the Hookworm is smaller than the larva of Ascaris, thus causing less damage. - "Ground itch," a pruritic papule or vesicle, can occur at the site of entry of the larvae into the skin.  Epidemiology : - Hookworm is found worldwide, especially in tropical areas. In the United States, Necator is endemic in the rural southern states. - Walking barefooted on soil predisposes to infection. An important public health measure was requiring children to wear shoes to school.  Laboratory Diagnosis : - Diagnosis is made microscopically by observing the eggs in the stools. Egg is rounded or oval & it is transparent, the ova which appear segmented or lobulated are surrounded by a black membrane or shell. If they are kept more than 12 hours in the dark they hatch and release the larvae. - The Larvae has a long oral cavity but no esophageal bulb. - Occult blood in the stools is frequent. Eosinophilia is typical. - Iron deficiency anemia must be diagnosed & other causes of anemia must be excluded. -  Treatment : - Mebendazole (Vermox) is effective. - Iron supplement is necessary.  Prevention : - Disposing of sewage properly and wearing shoes are effective means of prevention. 86 Nematodes  Strongyloides stercoralis - Strongyloides stercoralis causes strongyloidiasis. - It is the only intestinal Nematode that can exist in a free living state.  Important Properties : - S. stercoralis has two distinct life cycles, one within the human body and the other free-living in the soil. - The life cycle in the human body begins with the penetration of the skin, usually of the feet, by infectious (filariform) larvae and their migration to the lungs. They enter the alveoli, pass up the bronchi and trachea, and then are swallowed. - In the small intestine, the larvae molt into adults that enter the mucosa and produce eggs. - The eggs usually hatch within the mucosa, forming rhabditiform larvae that are passed in the feces. - Some larvae molt to form filarial larvae, which penetrate the intestinal wall directly without leaving the host and migrate to the lungs (autoinfection). - In immunocompetent patients, this is an infrequent, clinically unimportant event, but in immunocompromised patients, e.g., those who have AIDS or are taking high- dose corticosteroids, or patients who are severely malnourished, autoinfection can lead to massive reinfection, with larvae passing to many organs and with severe, sometimes fatal consequences. - If larvae are passed in the feces and enter warm, moist soil, they molt through successive stages to form adult male and female worms. After mating, the entire life ‫ شوفي ميل وفيميل وقع منك‬- cycle of egg, larva, and adult can occur in the soil. ،‫في التربة تزوجو وعملو بيض‬ - After several free-living cycles, filarial larvae are formed. When they contact skin,‫رفا انت‬A‫ طلعت ال‬،‫فقش البيض‬ ‫ عملت لك دودة‬،‫دعتسها وجاتك‬ they penetrate and again initiate the parasitic cycle within humans. ‫نثى عملت‬M‫في بطنك ثم الدودة ا‬ - intestinal ‫ فقس في ال‬،‫بيض‬ ‫ طلعت رومبيديفىرم‬،‫ حقك‬wall  Pathogenesis & Clinical Findings : and you ‫رفا لو عندك امساك‬M ‫ تتحول‬are under steroids - Most patients are asymptomatic, especially those with a low worm burden. retroinfection ‫ري والقم‬A‫ف‬ - Adult female worms in the wall of the small intestine can cause inflammation, ‫رفا خرجت وشققت ظهرك‬A‫لو ال‬ currens larva ‫القم‬ causing upper abdominal pain similar to ulcer pain and diarrhoea alternating with constipation. - Heavy infection in children: may cause malabsorption, because the worms are in the small intestine. - In autoinfection, the penetrating larvae may cause sufficient damage to the intestinal mucosa that sepsis caused by enteric bacteria can occur. - Larvae in the lungs can produce a pneumonitis similar to that caused by Ascaris & Hookworms (Loeffler’s syndrome). - Pruritus (ground itch) can occur at the site of larval penetration of the skin, as with hookworm. 87 Nematodes   Epidemiology : - Strongyloidiasis occurs primarily in the tropics, especially in Southeast Asia. Its geographic pattern is similar to that of hookworm because the same type of soil is required. In the United States, Strongyloides is endemic in the southeastern states.  Laboratory Diagnosis : - Diagnosis depends on finding larvae, rather than eggs, in the stool. - As with many nematode infections in which larvae migrate through tissue, eosinophilia can be striking in early infection but moderate in chronic infection. - Larvae can also be found by examination of the duodenal content either directly by duodenal aspirate or indirectly by String test (enterotest capsule). - Larvae of Strongyloides should be differentiated from larvae of the Hookworms. In Strongyloides the oral cavity is short and there is an esophageal bulb, while in the Hookworms the oral cavity is long and there is no esophageal bulb. - Serologic tests are useful when the larvae are not visualized e.g. ELISA, DAT. - An enzyme immunoassay that detects antibody to larval antigens is available through the CDC in Atlanta.  Treatment : ** - Ivermectin is the drug of choice. Thiabendazole is an alternative drug.  Prevention : - Prevention involves disposing of sewage properly and wearing shoes. 88 Nematodes  Enterobius vermicularis - Enterobius vermicularis causes pinworm infection (enterobiasis).  Important Properties : - The life cycle is confined to humans. The infection is acquired by ingesting the worm eggs. The eggs hatch in the small intestine, where the larvae differentiate into adults and migrate to the colon. The adult male and female worms live in the colon, where mating occurs. - At night, the female migrates thro. The anus and releases thousands of fertilized eggs on the perianal skin and into the environment (this causes severe itching). - Within 6 hours, the eggs develop into embryonated eggs and become infectious. - Reinfection can occur if they are carried to the mouth by fingers after scratching the itching skin. - The eggs may remain viable & infective for many weeks in clothes, utensils & in the dust. - Rarely, retro-infection may occur I.e. when the egg hatches in the perianal region and the larva finds its way back to the intestine thro. The anus.  Pathogenesis & Clinical Findings : - Perianal pruritus is the most prominent symptom. - Pruritus is thought to be an allergic reaction to the presence of either the adult female or the eggs. - Scratching predisposes to secondary bacterial infection, UTI in males or vulvovaginitis in females. - Worms in the appendix may obstruct it causing acute appendicitis.  Epidemiology : - Enterobius is found worldwide and is the most common helminth in the United States. - Children younger than 12 years of age are the most commonly affected group.  Laboratory Diagnosis : - The eggs are recovered from perianal skin by using the Scotch tape technique (silotape technique) and can be observed microscopically. - The ovum is very characteristic, it is asymmetrical or oval in shape, flat in one side & convex in the other side (D-shaped), and it is transparent & contains the larvae. - Unlike those of other intestinal nematodes, these eggs are not found in the stools. The small, whitish adult female worms can be found in the stools or near the anus of diapered children. Males are rarely seen. 89 Nematodes  - The head of the worm is surrounded by 2 cervical alae and this helps to distinguish the worm in cross section in the appendix. - No serologic tests are available.  Treatment : - Mebendazole is effective. They kill the adult worms in the colon but not the eggs, so retreatment in 2 weeks is suggested (repeat treatment). Reinfection is very common.  Prevention : - There are no means of prevention. Instruct the pt. to wash his hands & clothes to prevent spread of the disease to other members in the family. Trichuris trichiura  Trichuris trichiura causes whipworm infection (trichuriasis).  Important Properties : - The worm is about 3-5 cm. The anterior part is thin & is occupied by the esophagus in both male & female. It is partially buried in the mucosa of the large intestine. The posterior part is thick and is occupied by the uterus in females, while in males it is curved thro. 360* and can be used for identification. - Humans are infected by ingesting worm eggs in food or water contaminated with human feces. The eggs hatch in the small intestine, where the larvae differentiate into immature adults. - These forms migrate to the colon, where they mature, mate, and produce thousands of fertilized eggs daily, which are passed in the feces. Eggs deposited in warm, moist soil form embryos. When the embryonated eggs are ingested, the cycle is completed. - "Whip like" appearance of the adult worm is very characteristic.  Pathogenesis & Clinical Findings : - Although adult Trichuris worms burrow their hair like anterior ends into the intestinal mucosa, they do not cause significant anemia, unlike the hookworms. They feed on tissue juices not on blood. - Trichuris may cause diarrhea, but most infections are asymptomatic. - Trichuris may also cause rectal prolapse in children with heavy infection. Prolapse results from increased peristalsis that occurs in an effort to expel the worms, moreover high numbers of embedded worms in the rectum cause edema. The whitish worms may be seen on the prolapsed mucosa. 90 Nematodes  - It may also cause chronic diarrhoea (dysentery), ulceration in the bowel, wasting & rarely anemia. - The pts. Are predisposed to develop Amebiasis & Bacillary dysentery because the damage caused by the worm enhances entry of these organisms. (Complications)  Epidemiology : - Whipworm infection occurs worldwide, especially in the tropics; more than 500 million people are affected. - In the United States, it occurs mainly in the southern states.  Laboratory Diagnosis : - Diagnosis is based on finding the typical eggs, i.e., barrel-shaped (lemon-shaped) with a plug at each end, yellow brown in color, in the stool. - If rectal prolapse occurs, worms can be seen attached to the rectal mucosa. - Proctoscopy: red, ulcerated mucosa in the rectum, with worms attached to it. - Eosinophilia is mild or absent.  Treatment : - Mebendazole is the drug of choice. Albendazole is an alternative.  Prevention :  Proper disposal of feces prevents transmission. Trichinella spiralis  Trichinella spiralis causes trichinosis.  It is an intestinal Nematode , but differs in that : 1. Man is not the normal host. 2. Females are viviparous. 3. The worm stays in the intestines only for a very short time and then migrates to muscles where they become encysted => considered as tissue Nematodes.  Important Properties :  Any mammal can be infected, but pigs are the most important reservoirs of human disease in the United States (except in Alaska, where bears constitute the reservoir).  Humans are infected by eating raw or undercooked meat containing larvae encysted in the muscle.  The larvae excyst and mature into adults within the mucosa of the small intestine. 91 Nematodes   Eggs hatch within the adult females, and larvae are released and distributed via the bloodstream to many organs; however, they develop only in striated muscle cells.  Within these "nurse cells," they encyst within a fibrous capsule and can remain viable for several years but eventually calcify.  The parasite is maintained in nature by cycles within reservoir hosts, primarily swine and rats.  Humans are end-stage hosts, because the infected flesh is not consumed by other animals.  Pathogenesis & Clinical Findings :  A few days after eating undercooked meat, usually pork, and the patient experiences diarrhea followed 1 to 2 weeks later by fever, muscle pain, periorbital edema, and eosinophilia.  Subconjunctival hemorrhages are an important diagnostic criterion. D.D of subconjunctival Hemorrhage: Infective Endocarditis, Whooping cough (B.pertussis) & Leptospirosis.  Signs of cardiac and central nervous system disease are frequent, because the larvae migrate to these tissues as well.  Death, which is rare, is usually due to congestive heart failure or respiratory paralysis.  Epidemiology :  Trichinosis occurs worldwide, especially in Eastern Europe and West Africa. In the United States, it is related to eating home-prepared sausage, usually on farms where the pigs are fed uncooked garbage. Bear and seal meat also are sources.  In many countries, the disease occurs primarily in hunters who eat undercooked wild game.  Laboratory Diagnosis :  Muscle biopsy reveals larvae within striated muscle.  Serologic tests, especially the bentonite flocculation test, become positive 3 weeks after infection.  Treatment :  There is no treatment for trichinosis, but for patients with severe symptoms, steroids plus mebendazole can be tried.  Thiabendazole is effective against the adult intestinal worms early in infection.  Prevention :  The disease can be prevented by properly cooking pork and by feeding pigs only cooked garbage. 92 Nematodes  Tissue Nematodes  They cause a group of diseases collectively known as Filariasis.  They are viviparous I.e. give birth to larvae. The larval stage is called Microfilaria.  Intermediate host is usually insects.  Species that cause Filariasis : 1. Wuchereria bancrofti. 2. Brugia malayi. 3. Onchocerca volvulus. 4. Loa loa.  They are characterized by periodicity : 1. Nocturnal periodicity :  The appearance of Microfilaria in blood mainly at night, reaching maximum number between 10 pm & 2 am. In the day they rest in the capillaries. E.g. W.Bancrofti & B.Malayi. Transmitted mainly by night feeding insects. 2. Diurnal periodicity :  Microfilaria are found in blood only during the day, they are absent during night. E.g. Loa loa. Transmitted mainly by day feeding insects.  Onchocerca Microfilaria are not found in blood (in subcutaneous tissue).  The vector : 1. W.Bancrofti is transmitted by mosquitoes, mainly Anopheles, Aedes & Culex. 2. B.Malayi is transmitted mainly by mosquitoes Anopheles & Mansonia. 3. Onchocerca volvulus is transmitted by a fly called Simulium. 4. Loa loa is transmitted by a fly called Chrysops. - - They are treated by Diethylcarbamazine (DEC), except Onchocerca volvulus - - Diagnosis can be made by demonstrating the shape of microfilariae microscopically. - 93 Nematodes  Wuchereria bancrofti  Wuchereria bancrofti causes filariasis. Brugia malayi causes filariasis in Malaysia.  Elephantiasis is a striking feature of this disease.  Tropical pulmonary eosinophilia is an immediate hypersensitivity reaction to W. bancrofti in the lung.  Important Properties : - They are equipped with sheath. The head is rounded, tail is tapering, they have nuclei in all the body but not reaching the tip of the tail. - Humans are infected when the female mosquito (especially Anopheles and Culex species) deposits infective larvae on the skin while biting. - The larvae penetrate the skin, enter a lymph node and after 1 year, mature to adults that produce microfilariae. These circulate in the blood, chiefly at night, and are ingested by biting mosquitoes. - Within the mosquito, the microfilariae produce infective larvae (in muscles of the thorax) that are transferred with the next bite. - There is no multiplication in the insect I.e. one microfilaria gives rise to one infective stage. - Humans are the only definitive hosts.  Pathogenesis & Clinical Findings : - Adult worms in the lymph nodes cause inflammation that eventually obstructs the lymphatic vessels, causing edema. Massive edema of the legs is called elephantiasis. Note that microfilariae do not cause symptoms. - Early infections are asymptomatic. Later, fever, lymphangitis, and cellulitis develop. - Gradually, the obstruction leads to edema and fibrosis of the legs and genitalia, especially the scrotum. Choluria may develop (a condition due to rupture of the lymphatics in the kidney leading to presence of lymph in the urine). - All these manifestations are due to the presence of the adult worm. - Elephantiasis occurs mainly in patients who have been repeatedly infected over a long period. Tourists, who typically are infected only once, do not get elephantiasis. - Wolbachia species are rickettsia-like bacteria found intracellularly within filarial nematodes such as Wuchereria and Oncocerca. - Wolbachia release endotoxin-like molecules that are thought to play a role in the pathogenesis of Wuchereria and Oncocerca infections. - Evidence for this includes the use of doxycycline, which kills the Wolbachia resulting in a reduction of the inflammatory response to the nematode infection. 94 Nematodes  - Tropical pulmonary eosinophilia is characterized by coughing and wheezing, especially at night. These symptoms are caused by microfilariae in the lung that elicit an immediate hypersensitivity reaction characterized by a high immunoglobulin E (IgE) concentration and eosinophilia.  Epidemiology : - This disease occurs in the tropical areas of Africa, Asia, and Latin America. The species of mosquito that acts as the vector varies from area to area. Altogether, 200 to 300 million people are infected.  Laboratory Diagnosis : - Clinical features & high eosinophilia. - Thick blood smears taken from the patient at night reveal the microfilariae (have a sheath and the nuclei don't extend to the tip of the tail). - Serologic tests are not useful.  Treatment : - Diethylcarbamazine (DEC) is effective only against microfilariae; no drug therapy for adult worms is available. - It is preferable to begin with a small dose to minimize the side effects of the drug. The main side effect is allergic reaction to the rapid death of the Microfilaria.  Prevention :  Prevention involves mosquito control with insecticides and the use of protective clothing, mosquito netting, and repellents. Brugia malayi - Causes lymphatic Filariasis. - Transmitted by Anopheles & Mansonia. - Periodicity is nocturnal in countries where Anopheles transmit the disease. - Periodicity is both nocturnal & diurnal where Mansonia transmit the disease. - Clinical presentation is similar to W.Bancrofti except that in B.Malayi infection there is no scrotal involvement. - Diagnosis is based on seeing Microfilaria similar to W.Bancrofti but has a nucleus at the tip of the tail (only one nucleus). - Treated by DEC (same as W.bancrofti). 95 Nematodes  Onchocerca  Onchocerca volvulus causes onchocerciasis (River blindness).  Important Properties : - Humans are infected when the female blackfly, Simulium (Simulium domnosum mainly), deposits infective larvae while biting. - The larvae enter the wound and migrate into the subcutaneous tissue, where they differentiate into adults, usually within dermal nodules. The female produces microfilariae that are ingested when another blackfly bites. The microfilariae develop into infective larvae in the fly to complete the cycle. - Humans are the only definitive hosts.  Pathogenesis & Clinical Findings : - All clinical manifestations are due to the reaction caused by the dead Microfilaria and not by the adult worms except Onchocercoma. - Inflammation occurs in subcutaneous tissue, and pruritic papules and painless nodules (Onchocercoma) form in response to the adult worm proteins. These nodules are mainly found over bony prominences like the Pelvis or the face. - Microfilariae migrate through subcutaneous tissue, ultimately concentrating in the eyes. There they cause lesions that can lead to blindness. - Loss of subcutaneous elastic fibers leads to wrinkled skin, which is called "hanging groin" when it occurs in the inguinal region. - Thickening, scaling, and dryness of the skin accompanied by severe itching are the manifestations of a dermatitis often called "lizard skin" or Onchodermatitis. - The role of Wolbachia in the pathogenesis of onchocerciasis has been discussed earlier in "Wuchereria."  In sudan : - Abu Hamad dermatitis. - In South Sudan => dermatitis & blindness occur.  In Yemen : - Sowdah (black disease): a severe allergic response affecting one limb with darkening of the skin.  Note : - Ocular lesions affect either the anterior chamber or the posterior chamber. - Anterior chamber lesions => Sclerosing keratitis & Iritis are the main causes of blindness (allergic reaction to dead Microfilaria). - Posterior chamber lesions => Chorioretinitis +/- atrophy leads to blindness. 96 Nematodes   Epidemiology : - Millions of people are affected in Africa and Central America. - The disease is a major cause of blindness. It is called river blindness, because the blackflies develop in rivers and people who live along those rivers are affected. - Infection rates are often greater than 80% in areas of endemic infection. -  Laboratory Diagnosis : - Biopsy of the affected skin reveals microfilariae. Microfilaria are unsheathed and the nuclei do not reach the tip of the tail. - Examination of the blood for microfilariae is not useful because they do not circulate in the blood (unlike W.bancrofti & Loa loa). Eosinophilia is common. - Mazzotti test: give a small dose of DEC that kills the Microfilaria causing serious allergic reaction in heavy infection. Not justified unless in mild infection i.e. when the skin snip is negative. o Serologic tests are not helpful.  Treatment : - Ivermectin is effective against microfilariae but not adults. DEC is also useful. - Skin nodules can be removed surgically, but new nodules can develop; therefore, a surgical cure is unlikely in areas of endemic infection.  Prevention : - Prevention involves control of the blackfly with insecticides. Ivermectin prevents the disease. 97 Nematodes  Loa loa  Loa loa (eye worm) causes loiasis.  Important Properties : - Humans are infected by the bite of the deer fly (mango fly), Chrysops, which deposits infective larvae on the skin. - The larvae enter the bite wound, wander in the body, and develop into adults. - The females release microfilariae that enter the blood, particularly during the day. - The microfilariae are taken up by the fly during a blood meal and differentiate into infective larvae, which continue the cycle when the fly bites the next person.  Pathogenesis & Clinical Findings : - There is no inflammatory response to the microfilariae or adults, but a hypersensitivity reaction causes transient, localized, non-erythematous, subcutaneous edema (Calabar swellings). Characterized by reappearance at a site after disappearance from another site. - The most dramatic finding is an adult worm crawling across the conjunctiva of the eye, a harmless but disconcerting event.  Epidemiology : - The disease is found only in tropical central and West Africa, the habitat of the vector Chrysops.  Laboratory Diagnosis : - Diagnosis is made by visualization of the microfilariae in a blood smear. Microfilaria are characterized by presence of sheath, moreover the nuclei extend to the tip of the tail. - There are no useful serologic tests.  Treatment : - Diethylcarbamazine (DEC) eliminates the microfilariae and may kill the adults. Worms in the eyes may require surgical excision. - Ivermectin is contraindicated because it causes post-therapeutic encephalopathy.  Prevention : - Control of the fly by insecticides can prevent the disease. 98 Nematodes  Dracunculus medinensis  Dracunculus medinensis (guinea fire worm or Medina worm) causes dracunculiasis.  Important Properties : - Humans are infected when tiny crustaceans (copepods) containing infective larvae are swallowed in drinking water. - The larvae are released in the small intestine and migrate into the body, where they develop into adults. They mature in the connective tissue of the retroperitoneal space. - Meter-long adult females reach gravidity in about one year, cause the skin to ulcerate and then release motile rhabditiform larvae into fresh water. - Copepods eat the larvae, which molt to form infective larvae. The cycle is completed when these are ingested in the water.  Pathogenesis & Clinical Findings : - The adult female produces a substance that causes inflammation, blistering, and ulceration of the skin, usually of the lower extremities. The inflamed papule burns and itches, and the ulcer can become secondarily infected (secondary infections & cellulitis are common, particularly if the worm is ruptured during the process of extraction). - Few days before the formation of the blisters, the patient may have fever & generalized urticaria. - Manifestations are thought to represent allergic reaction to prematurely liberated larvae. - Diagnosis is usually made clinically by finding the worm in the skin ulcer.  Epidemiology : - The disease occurs over large areas of tropical Africa, the Middle East, and India. Tens of millions of people are infected.  Laboratory Diagnosis : - Clinical presentation is characteristic, well known in endemic areas. - If a worm is seen protruding from an ulcer, placing a small amount of water on the worm results in discharge of larvae that can be examined microscopically. The anterior end is round while the posterior end is tapering and it is always coiled. - Dead & calcified worms can be seen in X-ray in chronic areas. - Eosinophilia. 99 Nematodes   Treatment : 1. Traditional treatment :  The time-honored treatment consists of gradually extracting the worm by winding it up on a stick over a period of days. The worm should not be broken inside the tissue because: the fluid released can cause severe allergy and the worm will retract inside the tissues with severe inflammation & destruction of tissues. 2. Anti-helminths: Thiabendazole or Metronidazole makes the worm easier to extract and relief the symptoms. 3. Antibiotics: to prevent secondary bacterial infection. 4. Anti-tetanus vaccine should be given. The ulcer should be cleaned & dressed clearly to prevent bacterial infection.  Prevention : - Prevention consists of filtering or boiling drinking water. 100 Nematodes  Animal Nematodes Toxocara - Toxocara canis is the major cause of visceral larva migrans. - T. cati and several other related nematodes also cause this disease.  Important Properties : - The definitive host for T. canis is the dog. - The adult T. canis female in the dog intestine produces eggs that are passed in the feces into the soil. Humans ingest soil containing the eggs, which hatch into larvae in the small intestine. - The larvae migrate too many organs, especially the liver, brain, and eyes. The larvae eventually are encapsulated and die. - The life cycle is not completed in humans; humans are therefore accidental, dead- end hosts.  Pathogenesis & Clinical Findings : - Pathology is related to the granulomas that form around the dead larvae as a result of a delayed hypersensitivity response to larval proteins. - The most serious clinical finding is blindness associated with retinal involvement. Fever, hepatomegaly, and eosinophilia are common. Nephritis, cardiac dysfunction & sometimes neurological manifestations occur.  Epidemiology : - Young children are primarily affected, because they are likely to ingest soil containing the eggs. - T. canis is a common parasite of dogs in the United States.  Laboratory Diagnosis : - Serologic tests are commonly used, but the definitive diagnosis depends on visualizing the larvae in tissue. - The presence of hypergammaglobulinemia and eosinophilia supports the diagnosis.  Treatment : - The treatment of choice is either albendazole or mebendazole, combined with steroids, but there is no proven effective treatment. DiEthylCarbamazine (DEC) for 21 days is also an option. - Many patients recover without treatment.  Prevention :  Dogs should be dewormed, and children should be prevented from eating soil. 101 Nematodes  Ancylostoma - Cutaneous larva migrans is caused by the filariform larvae of Ancylostoma caninum (dog hookworm) and Ancylostoma braziliense (cat hookworm), as well as other nematodes e.g. Strongyloides of animals. - The organism cannot complete its life cycle in humans. - The larvae penetrate the skin and migrate through subcutaneous tissue for several months causing a severe localised allergic reaction and as they migrate they form tortuous tunnels. The progression of the anterior end of the larvae every few days can be easily observed. Thus lesions are called ("creeping eruption") and they are extremely pruritic. - The disease occurs primarily in the southern United States, in children and construction workers who are exposed to infected soil. - The diagnosis is made clinically; the laboratory is of little value. - Oral or topical thiabendazole is usually effective. Minor animal Nematodes Angiostrongylus - The larvae of the rat lung nematode Angiostrongylus cantonensis cause eosinophilic meningitis, i.e., a meningitis characterized by many eosinophils in the spinal fluid and in the blood. Usually at least 10% of the white cells are eosinophils. - The larvae are typically ingested in undercooked seafood, such as crabs, prawns, and snails. Infection by this organism most often occurs in Asian countries. - The diagnosis is made primarily on clinical grounds, but occasionally, the laboratory will find a larva in the spinal fluid. - There is no treatment. Most patients recover spontaneously without major sequelae. - Eosinophilic meningitis is also caused by the larvae of two additional nematodes. - Gnathostoma spinogram, an intestinal nematode of cats and dogs, is acquired by eating undercooked fish and Baylisascaris procyonis, a raccoon roundworm, is acquired by accidentally ingesting raccoon feces. - These organisms cause more severe disease than Angiostrongylus, and fatalities occur. - Albendazole may be effective against Gnathostoma, but there is no treatment for Baylisascaris. 102 Nematodes  Anisakis - Anisakiasis is caused by the larvae of the nematode, Anisakis simplex. - The larvae are ingested in raw seafood and can penetrate the submucosa of the stomach or intestine. - The adult worms live in the intestines of marine mammals such as whales, dolphins, and seals. - The eggs produced by the adults are eaten by crustaceans, which are then eaten by marine fish such as salmon, mackerel, and herring. - Gastroenteritis, abdominal pain, eosinophilia, and occult blood in the stool typically occur. - Acute infection can resemble appendicitis, and chronic infection can resemble gastrointestinal cancer. - Most cases in the United States have been traced to eating sushi and sashimi (especially salmon and red snapper) in Japanese restaurants. - The diagnosis is typically made endoscopically or on laparotomy. - Microbiologic and serologic tests are not helpful in the diagnosis. - There are no effective drugs. Surgical removal may be necessary. Prevention consists of cooking seafood adequately or freezing it for 24 hours before eating. - Another member of the Anisakid family of nematodes is Pseudoterranova decepiens, whose larvae cause a noninvasive form of anisakiasis. - The larvae are acquired by eating undercooked fish and cause vomiting and abdominal pain. - The diagnosis is made by finding the larvae in the intestinal tract or in the vomitus. - There is no drug treatment. The larvae can be removed during endoscopy 103 Nematodes