Protozoa-Helminths-Arthropods of Medical Importance PDF

PROTOZOA- HELMINTHS- ARTHROPODS OF MEDICAL IMPORTANCE BEDİA DİNÇ E. histolytica Causes amebic dysentery and liver abscess. The life cycle has two stages: the motile ameba (trophozoite) and the nonmotile cyst Trophozoite; found within the intestinal and extraintestinal lesion...

PROTOZOA- HELMINTHS- ARTHROPODS OF MEDICAL IMPORTANCE BEDİA DİNÇ E. histolytica Causes amebic dysentery and liver abscess. The life cycle has two stages: the motile ameba (trophozoite) and the nonmotile cyst Trophozoite; found within the intestinal and extraintestinal lesions and in diarrheal stools and cyst; in nondiarrheal stools. Cysts; killed by boiling but not by chlorination of water supplies. They are removed by filtration of water. The cyst has four nuclei; an important diagnostic criterion. Antibodies are formed against trophozoite antigens in invasive amebiasis. Previous infection does not prevent reinfection. Pathogenesis & Epidemiology Acquired by ingestion of cysts that are transmitted primarily by the fecal-oral route in contaminated food and water. Anal-oral transmission (e.g., among male homosexuals) also occurs, no animal reservoir. The ingested cysts differentiate into trophozoites in the ileum and trophozoites invade the colonic epithelium and secrete enzymes that cause localized necrosis. Flask shaped ulcer; as the lesion reaches the muscularis layer, which can undermine and destroy large areas of the intestinal epithelium. Progression into the submucosa leads to invasion of the portal circulation by the trophozoites Most frequent site of systemic disease is the liver, where abscesses containing trophozoites form. E. histolytica infection; found worldwide but occurs most frequently in tropical countries with poor sanitation.  Acute intestinal amebiasis; dysentery (i.e., bloody, mucus- containing diarrhea) accompanied by lower abdominal discomfort, flatulence, and tenesmus. Chronic amebiasis; low-grade symptoms such as occasional diarrhea, weight loss, and fatigue. 90% of those infected have asymptomatic infections; !!!they may be carriers, whose feces contain cysts that can be transmitted to others. Ameboma; a granulomatous lesion called in the cecal or rectosigmoid areas of the colon in some patients. Amebic abscess of the liver; characterized by right- upperquadrant pain, weight loss, fever, and a tender, enlarged liver. Right- lobe abscesses can penetrate the diaphragm and cause lung disease. Most cases of amebic liver abscess occur in patients who have not had overt intestinal amebiasis and aspiration of the liver abscess  Trophozoites in diarrheal stools or cysts in formed stools. Diarrheal stools should be examined within 1 hour of collection to see the ameboid motility of the trophozoite (at least three specimens). Trophozoites characteristically contain ingested red blood cells.  E. histolytica can be distinguished from other amebas by two major criteria; the nature of the nucleus of the trophozoite (E. histolytica nucleus has a small Central nucleolus and fine chromatin granules along the border of the nuclear membrane) cyst size and number of its nuclei (mature cysts of E. histolytica are smaller than those of Entamoeba coli and contain four nuclei, whereas E. coli cysts have eight nuclei).  Microscopic examination wet mount in saline, an iodine-stained wet mount, fixed, trichrome stained preparation, each of which brings out different aspects of cyst morphology. E. histolytica antigen test (rapid test or ELISA) PCR-based assays Serologic testing; useful for diagnosis of invasive amebiasis. Indirect hemagglutination test is usually positive in patients with invasive disease but is frequently negative in asymptomatic individuals who are passing cysts. Treatment for symptomatic intestinal amebiasis or hepatic abscesses; metronidazole (Flagyl) or tinidazole. Prevention involves avoiding fecal contamination of food and water and handwashing. G. Lamblia (G. Duodenalis/G. intestinalis) Causes giardiasis. Life cycle; trophozoite and cyst The trophozoite is pear-shaped with two nuclei, four pairs of flagella, and a suction disk with which it attaches to the intestinal wall, oval cyst is thick-walled with four nuclei and several internal fibers. Each cyst gives rise to two trophozoites during excystation in the intestinal  Transmission; ingestion of cysts in fecally contaminated food and water. Excystation happens in the duodenum, where the trophozoite attaches to the gut wall but does not invade the mucosa and does not enter the bloodstream. The trophozoite causes inflammation of the duodenal mucosa, leading to malabsorption of protein and fat.  Found worldwide. Approximately half of those infected are asymptomatic carriers who continue to excrete the cysts for years. IgA deficiency greatly predisposes to symptomatic infection. Outbreaks; related to contaminated water supplies and chlorination does not kill the cysts, but filtration removes them. Many species of mammals as well as humans act as the reservoirs. The incidence is high among children in day care centers, male homosexuals and among patients in mental hospitals.  Watery (nonbloody), foul-smelling diarrhea accompanied by nausea, anorexia, flatulence, and abdominal cramps persisting for weeks or months. Trophozoites or cysts or both in diarrheal stools and cysts in formed stools (e.g., in asymptomatic carriers). ELISA that detects Giardia antigen in the stool. String test, which consists of swallowing a weighted piece of string until it reaches the duodenum; trophozoites adhere to the string and can be visualized after withdrawal of the string. PCR (multiplex PCR) Treatment; either tinidazole (Tindamax) or metronidazole (Flagyl). Prevention; drinking boiled, filtered, or iodine-treated water in endemic areas  C. hominis (formerly known as Causes cryptosporidiosis, the main C.parvum) symptom of which is diarrhea; most severe in immunocompromised patients (AIDS). Acquired by fecal-oral transmission of oocysts from either human sources (primarily) or from animal sources Invasion does not occur. The pathogenesis of the diarrhea is uncertain; no toxin has been identified.  Cryptosporidia cause diarrhea worldwide. Inadequate purification of drinking water or swimming in fecally contaminated pools and lakes; source of outbreaks. The cysts are highly resistant to chlorination but are killed by pasteurization and can be removed by filtration. Watery, nonbloody diarrhea causing large fluid loss in immunocompromised patients; symptoms persist for long priods but self-limited in immunocompetent patients. Diagnosis; oocysts in fecal smears when using a modified Kinyoun acid-fast Cryptosporidium antigen test in the stool PCR Nitazoxanide for HIV positive patients, paromomycin may be useful in reducing diarrhea. Purifıcation of the water supply, including filtration to remove the cysts UROGENITAL PROTOZOA- TRICHOMONAS T. vaginalis causes trichomoniasis. A pear-shaped organism with a Central nucleus and four anterior flagella Has an undulating membrane that extends about two-thirds of its length. Exists only as a trophozoite; no cyst form.  Pathogenesis & Epidemiology Transmitted by sexual contact Primary locations; the vagina and the prostate. Found only in humans; no animal reservoir. One of the most common infections worldwide. The frequency of symptomatic disease is highest among sexually active women in their thirties and lowest in postmenopausal women. Asymptomatic infections; common in both men and women.  Clinical Findings About 70% of affected people; no symptoms when infected Symptoms typically begin 5 to 28 days after exposure In women; a watery, foul-smelling, greenish vaginal discharge accompanied by itching and burning In men; usually asymptomatic, but about 10% of infected men have urethritis. Laboratory Diagnosis Wet mount of vaginal discharge; the pear-shaped trophozoites have a typical jerky motion Nucleic acid amplification tests (NAATs); highly specific and sensitive. Multiplex PCR tests Rapid tests No serologic test. Treatment & Prevention Tinidazole (Tindamax) Metronidazole (Flagyl) Used for both partners to prevent reinfection. About 20% of people get infected again within three months of treatment. Maintenance of the low pH of the vagina is helpful. Condoms to limit transmission. No prophylactic drug or vaccine.  Complications; Associated with increased risk of transmission and infection of HIV May cause a woman to deliver a low-birth-weight or premature infant The role of Trichomonas infection in causing cervical cancer is unclear, although trichomonas infection may be associated with co-infection with high-risk strains of HPV T. vaginalis infection in males has been found to cause asymptomatic urethritis and prostatitis. In the prostate it may create chronic inflammation that may eventually lead to prostate cancer  PLATYHELMINTHS-CESTODES (TAPEWORMS) Tapeworms consist of two main parts: a rounded head called a scolex a flat body consisting of multiple segments. Each segment is called a proglottid. 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 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. Acquisition of the infection; undercooked meat or fish containing the larvae is ingested. Taenia solium, Taenia saginata, Diphyllobothrium latum, and Echinococcus TAENIA-Taenia solium Adult form of T. Solium; taeniasis, larvae of T. Solium; cysticercosis. T. solium can be identified by its scolex, which has four suckers and a 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 Adult tapeworm is located in the human intestine after humans are infected by eating raw or undercooked pork containing the larvae, called  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. Cysts also are commonly found in skeletal muscle.  Diagnosis; observing gravid proglottids with 5 to 10 primary uterine branches in the stools. Eggs are found in the stools less often than are proglottids. Diagnosis of cysticercosis; demonstrating the presence of the cyst in tissue, usually by surgical removal or computed tomography (CT) scan. Serologic tests (ELISA); detect antibodies to T. solium antigens,but may be negative in neurocysticercosis. Treatment for the intestinal worms; praziquantel. Treatment for cysticercosis; either praziquantel or albendazole, but surgical excision may be necessary. Prevention; cooking pork adequately and disposing waste properly so that pigs cannot ingest human feces. Prevention of cysticercosis; treatment of patients to prevent autoinfection and handwashing to prevent contamination of food with the eggs. Taenia saginata T. saginata causes taeniasis. T. saginata larvae do not cause cysticercosis. 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.  Humans are infected by eating raw or undercooked beef containing larvae (cysticerci). Humans; definitive hosts and cattle; intermediate hosts.  Occurs worldwide but endemic in Africa, South America, and Eastern Europe. Most patients with adult tapeworms are asymptomatic, but malaise and mild cramps can occur. In some, proglottids appear in the stools and may even protrude from the anus. The proglottids are motile and may cause pruritus ani as they move on the skin adjacent to the anus.  Laboratory Diagnosis; observing gravid proglottids with 15 to 20 uterine branches in the stools. Eggs are found in the stools less often than are the proglottids. Treatment; praziquantel. Prevention; cooking beef adequately and disposing waste DIPHYLLOBOTHRIUM D. latum, the fish tapeworm, causes diphyllobothriasis 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 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 The longest of the tapeworms, measuring up to 13 m. Humans are infected by ingesting raw or undercooked fish containing larvae (called plerocercoid or sparganum larvae).  The cycle is completed when raw or undercooked fish is eaten by humans (definitive hosts).  D. latum causes little damage in the small intestine. Megaloblastic anemia; as a result of vitamin B12 deficiency caused by preferential uptake of the vitamin by the worm. Epidemiology is related to the ingestion of raw or inadequately cooked fish and to contamination of bodies of fresh water with human feces. Found worldwide but endemic in Scandinavia, northern Russia, Japan, Canada, and certain north-central States of the United States. Most patients are asymptomatic, but abdominal discomfort and diarrhea can occur. Diagnosis; observing the typical eggs (i.e., oval, yellow- brown eggs with an operculum at one end) in the stools. ECHINOCOCCUS E. granulosus (dog tapeworm) causes echinococcosis. The larva of E. granulosus causes unilocular hydatid cyst disease, E. multilocularis causes multilocular hydatid disease E. granulosus is composed of a scolex and only three proglottids, making it one of the smallest tapeworms Dogs; most important definitive hosts and intermediate hosts are usually sheep. Humans are almost always deadend intermediate hosts.  E. granulosus usually forms one large fluid-filled cyst (unilocular) that contains thousands of individual protoscoleces as well as many daughter cysts within the large cyst. Individual protoscoleces lying at the bottom of the large cyst are called “hydatid sand.” 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 anaphylactic shock can occur. Found primarily in shepherds living in the Mediterranean region, the Middle East, and Australia.  Many individuals with hydatid cysts are asymptomatic, but liver cysts may cause hepatic dysfunction. Cysts in the lungs can erode into a bronchus, causing bloody sputum, and cerebral cysts can cause headache and focal neurologic signs. Rupture of the cyst; fatal anaphylactic shock. Microscopic examination demonstrating the presence of brood capsules containing multiple protoscoleces  Serologic tests (e.g., the indirect hemagglutination test). Treatment; albendazole with or without surgical removal of the cyst. !!! Extreme care must be exercised to prevent release of the protoscoleces during surgery. A protoscolicidal agent (e.g., hypertonic şaline) should be injected into the cyst to kill the organisms and prevent accidental dissemination. Prevention; not feeding the entrails of slaughtered sheep to dogs.  TREMATODES Schistosoma species (blood flukes) Clonorchis sinensis (liver fluke) Paragonimus westermani (lung fluke) Fasciola hepatica Fasciolopsis buski Heterophyes heterophyes The life cycle; a sexual cycle in humans (definitive host) and asexual reproduction in freshwater snails (intermediate hosts) Transmission to humans; 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.  SCHISTOSOMA Schistosoma species cause schistosomiasis. Schistosoma mansoni and Schistosoma japonicum; gastrointestinal tract, Schistosoma haematobium; the urinary tract. Three species can be distinguished by the appearance of their eggs in the microscope: S. mansoni eggs have a prominent lateral spine, whereas S. japonicum eggs have a very small lateral spine and S. haematobium eggs have a terminal spine S. mansoni and S. japonicum adults live in the mesenteric veins, S. haematobium lives in the veins draining the urinary bladder.  Humans are infected when the free-swimming, fork- tailed cercariae penetrate the skin They differentiate to larvae (schistosomula), enter the blood, and are carried via the veins into the arterial circulation. S. mansoni and S. japonicum adults migrate against the portal flow to reside in the mesenteric venules. S. haematobium adults reach the bladder veins through the venous plexus between the rectum and the bladder.  Most of the pathologic findings; related with the presence of eggs in the liver, spleen, or wall of the gut or bladder. Eggs in the liver induce granulomas, leading to fibrosis, hepatomegaly, and portal hypertension. 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.  S. mansoni eggs damage the wall of the distal colon (inferior mesenteric venules), whereas S. 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. S. mansoni; found in Africa and Latin America, S. haematobium; found in Africa and the Middle East. S. japonicum; found only in Asia More than 150 million people in the tropical areas of Africa, Asia, and Latin America are affected  Most patients are asymptomatic, but chronic infections may become symptomatic. The acute stage; begins shortly after cercarial penetration; itching and dermatitis followed 2 to 3 weeks later by fever, chills, diarrhea, lymphadenopathy, and hepatosplenomegaly. Eosinophilia; in response to the migrating larvae. This stage usually resolves spontaneously. The chronic stage can cause significant morbidity and mortality.  In patients with S. mansoni or S. japonicum infection, gastrointestinal hemorrhage, hepatomegaly, and massive splenomegaly can develop. The most common cause of death is exsanguination from ruptured esophageal varices. S. haematobium; hematuria as the chief early complaint. Superimposed bacterial urinary tract infections occur frequently. “Swimmer’s itch,” which consists of pruritic papules,may occur. The papules are an immunologic reaction to the presence in the skin of the cercariae of nonhuman schistosomes.  Diagnosis; observing the characteristic ova in the feces or urine. S. mansoni; large lateral spine S. japonicum; rudimentary spine S. haematobium; large terminal spine Serologic tests are not useful. Moderate eosinophilia. Treatment; Praziquantel Prevention; proper disposal of human waste and eradication of the snail host when possible and avoiding swimming in areas of endemic infection.  CLONORCHIS C. sinensis causes clonorchiasis (Asian liver fluke infection) Humans are infected by eating raw or undercooked fish containing the encysted larvae (metacercariae).  The inflammatory response can cause hyperplasia and fibrosis of the biliary tract, but often there are no lesions. Endemic in China, Japan, Korea, and Indochina, where it affects about 20 million people. Most asymptomatic. In patients with a heavy worm burden, upper abdominal pain, anorexia, hepatomegaly, and eosinophilia can occur. Diagnosis; observing the typical small, brownish, operculated eggs in the stool Serologic tests are not useful. Treatment; Praziquantel Prevention; adequate cooking of fish and proper disposal of human waste. PARAGONIMUS P. westermani, the lung fluke, causes paragonimiasis. Humans are infected by eating raw or undercooked crab meat (or crayfish) containing the encysted larvae (metacercariae). The cycle is completed when undercooked infected crabs are eaten by humans.  Endemic in Asia and India. The main symptom; a chronic cough with bloody sputum. Dyspnea, pleuritic chest pain, and recurrent attacks of bacterial pneumonia occur. Diagnosis; observing the typical operculated eggs in sputum or feces Serologic tests are not useful. Treatment; Praziquantel Prevention; cooking crabs properly.  NEMATODES (Nemathelminthes) Roundworms 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 intestinal nematodes; Enterobius (pinworm), Trichuris (whipworm), Ascaris (giant roundworm), Necator and Ancylostoma (the two hookworms), Strongyloides (small roundworm), Trichinella. The important tissue nematodes Wuchereria, Onchocerca Loa  Enterobius, Trichuris, and Ascaris; transmitted by ingestion of eggs; the others are transmitted as larvae. Nematodes that migrate through tissue (e.g., Strongyloides, Trichinella, Ascaris, and the two hookworms Ancylostoma and Necator); increase in the number of eosinophils (eosinophilia) 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 [IL-5]) ENTEROBIUS Enterobius vermicularis causes pinworm infection (enterobiasis). Infection occurs only in humans; there is no animal reservoir or vector. 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 from the anus and releases thousands of fertilized eggs on the perianal skin and into the environment. Within 6 hours, the eggs develop into embryonated eggs and become infectious. Reinfection; if eggs are carried to the mouth by fingers after scratching the  Found worldwide especially among children younger than 12 years Prevention; washing hands when preparing food and washing bed sheets, towels, diapers, and clothing to remove eggs. The eggs are recovered from perianal skin by using the Scotch tape technique and can be observed microscopically Unlike those of other intestinal nematodes, these eggs are not found in the stools. The small, whitish adult worms can be found in the stools or near the anus of diapered children. No serologic tests. Treatment; albendazole, mebendazole, or pyrantel pamoate.  TRICHU RIS Trichuris trichiura causes whipworm infection (trichuriasis). Humans are infected by ingesting worm eggs in food or water contaminated with human feces  Does not cause significant anemia as the hookworms. Most asymptomatic; may cause diarrhea, also cause rectal prolapse in children with severe infection. Occurs worldwide, especially in the tropics Diagnosis; observing the typical eggs (barrelshaped [lemon-shaped] with a plug at each end) in the stool Treatment; Albendazole Prevention; Proper disposal of feces  ASCA RIS Ascaris lumbricoides causes ascariasis. Humans are infected by ingesting worm eggs in food or water contaminated with human feces  The major damage occurs during larval migration rather than from the presence of the adult worm in the intestine. Tissue reaction; the lungs, where inflammation with an eosinophilic exudate occurs in response to larval antigens. Most asymptomatic. Ascaris pneumonia with fever, cough, and eosinophilia can occur with a heavy larval burden. Abdominal pain and even obstruction can result from the presence of adult worms in the intestine.  Very common, especially in the tropics Diagnosis; detecting eggs (oval with an irregular surface) in the stools. Occasionally, the patient sees adult worms in the stools. Treatment; Albendazole, mebendazole, and ivermectin Prevention; proper disposal of feces.  ANCYLOSTOMA & NECATOR Ancylostoma duodenale (Old World hookworm) and Necator americanus (New World hookworm) cause hookworm infection. Humans are infected when filariform larvae in moist soil penetrate the skin, usually of the feet or legs  The major damage is due to the loss of blood at the site of attachment in the small intestine. 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. These symptoms occur in patients whose nutrition cannot compensate for the blood loss. “Ground itch,” a pruritic papule or vesicle, can occur at the site of entry of the larvae into the skin. The human hookworms also cause cutaneous larva migrans. Pneumonia with eosinophilia; during larval migration  Found worldwide, especially in tropical areas. Walking barefooted on soil predisposes to infection. Diagnosis; observing the eggs in the stools Occult blood in the stools is frequent. Eosinophilia. Treatment; albendazole, mebendazole, or pyrantel pamoate.  STRONGYLOIDES Strongyloides stercoralis causes strongyloidiasis. 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.  Most asymptomatic, especially those with a low worm burden. Adult female worms in the wall of the small intestine can cause inflammation, resulting in watery diarrhea. Larvae in the lungs; pneumonitis similar to that caused by Ascaris. Pruritus (ground itch) can occur at the site of larval penetration of the skin, as with hookworm. S. stercoralis also causes cutaneous larva migrans. Autoinfection can result in chronic strongyloidiasis characterized by intermittent abdominal pain, fluctuating rashes, and intermittent eosinophilia. In hyperinfection, the penetrating larvae may cause sufficient damage to the intestinal mucosa that sepsis caused by enteric bacteria, such as Escherichia coli and Bacteroides fragilis, can occur. Strongyloidiasis occurs primarily in the tropics, especially in Southeast Asia.  Diagnosis; finding larvae, rather than eggs, in the stool Eosinophilia; as with many nematode infections in which larvae migrate through tissue Serologic tests; useful when the larvae are not visualized. An enzyme immunoassay that detects antibody to larval antigens. Treatment; Ivermectin, Albendazole Prevention; disposing of sewage properly and wearing shoes. TRICHINE LLA Trichinella spiralis causes trichinosis. Any mammal can be infected, but pigs are the most important reservoirs of human disease Humans are infected by eating raw or undercooked meat containing larvae encysted in the muscle  A few days after eating undercooked meat, usually pork; diarrhea followed 1 to 2 weeks later by fever, muscle pain, periorbital edema, and eosinophilia. Subconjunctival hemorrhages; important diagnostic criterion. Since larvae migrate to these tissues, signs of cardiac and central nervous system disease are frequent Death; rare, usually due to congestive heart failure or respiratory paralysis.  Occurs worldwide, especially in Eastern Europe and West Africa primarily in hunters who eat undercooked wild game. Diagnosis; muscle biopsy reveals larvae within striated muscle Serologic tests, especially the bentonite flocculation test, become positive 3 weeks after infection. No effective treatment when the larvae have infected the muscle, but for patients with severe symptoms, steroids plus albendazole can be useful. Mebendazole is effective against the adult intestinal worms early in infection. Prevention; properly cooking pork and feeding pigs only with cooked garbage.  TISSUE NEMATODES-WUCHERERIA Wuchereria bancrofti causes filariasis. Elephantiasis; a striking feature of this disease. Tropical pulmonary eosinophilia is an immediate hypersensitivity reaction to W. bancrofti in the lung. Humans are infected when the female mosquito (especially Anopheles and Culex species) deposits infective larvae on the skin while biting. Humans are the only definitive hosts.  Adult worms in the lymph nodes cause inflammation; obstructing the lymphatic vessels, causing edema. Massive edema of the legs; elephantiasis 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. Elephantiasis occurs mainly in patients who have been repeatedly infected over a long period. Tropical pulmonary eosinophilia; 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 IgE concentration and eosinophilia.  Occurs in the tropical areas of Africa, Asia, and Latin America. Diagnosis; thick blood smears taken from the patient at night reveal the microfilariae Serologic tests are not useful. Treatment; Diethylcarbamazine; effective only against microfilariae; no drug therapy for adult worms is available. Prevention; mosquito control with insecticides and the use of protective clothing, mosquito netting, and repellents. ONCHOCERCA Onchocerca volvulus causes onchocerciasis. Humans are infected when the female blackfly deposits infective larvae while biting. Humans are the only definitive hosts.  Inflammation occurs in subcutaneous tissue, and pruritic papules and nodules form in response to the adult worm proteins. Microfilariae migrate through subcutaneous tissue, ultimately concentrating in the eyes where 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; manifestations of a dermatitis; called “lizard skin.” Millions of people are affected in Africa and Central America.  Major cause of blindness (called river blindness), because the blackflies develop in rivers and people who live along those rivers are affected Diagnosis; biopsy of the affected skin reveals microfilariae. Examination of the blood for microfilariae is not useful because they do not circulate in the blood. Eosinophilia is common. Serologic tests are not helpful. Treatment; Ivermectin is effective against microfilariae but not adults. Suramin kills adult worms but is quite toxic and is used particularly in those with eye disease. Prevention; control of the blackfly with insecticides. LOA LOA Loa loa causes loiasis. Humans are infected by the bite of the deer fly (mango fly) 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. There is no inflammatory response to the microfilariae or adults, but a hypersensitivity reaction causes transient, localized, nonerythematous, subcutaneous edema  The most dramatic finding; an adult worm crawling across the conjunctiva of the eye. Found only in tropical Central and West Africa Diagnosis; observing the microfilariae in a blood smear, no useful serologic tests. Treatment; Diethylcarbamazine Prevention; control of the fly by insecticides. DRACUNCULUS Dracunculus medinensis (guinea fire worm) causes dracunculiasis. Humans are infected when tiny crustaceans (copepods) containing infective larvae are swallowed in drinking water.  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. Diagnosis; clinically by finding the worm in the skin ulcer. Lab diagnosis; not performed Treatment; extracting the worm by winding it up on a stick over a period of days. Prevention; filtering or boiling drinking water.