Lec. 3 Parasitology PDF

College of medicine Lec.3 Parasitology Prof. Dr. Amal Kh. Kh. Helminthology Cestoda :...

College of medicine Lec.3 Parasitology Prof. Dr. Amal Kh. Kh. Helminthology Cestoda : Taenia species 1- There are two species of Taenia can infect human body which are T. saginata and T. solium, causing Taeniasis and cysticercosis. 2- Taeniasis is a small intestine infection of humans caused by Taenia species. 3- Cysticercosis is accidental infection in humans and develop in the musculature as well as CNS, eyes, skin. Taenia Saginata and Taenia Solium: Common Name Taenia saginata: Beef tapeworm Taenia solium: Pig tapeworm. History and Distribution :  T. saginata has been known as an intestjnal parasite of man from very ancient times. But it was only in 1782 when Goeze differentiated it from the pork tapeworm, T. solium. its life cycle was elucidated when Leuckart, in 1861, first experimentally demonstrated that cattle serve as the intermediate host for the worm.  The name Taenia is derived from the Greek word meaning tape or band. It was originally used to refer to most tapeworms, but is now restricted to the members of the Genus Taenia.  T: saginata is worldwide in distribution, but the infection is not found in vegetarians and those who do not eat beef.  T. solium is also worldwide in distribution except in the countries and communities, which proscribe pork as taboo. Habitat The adult worms of both T. saginata and T. solium() live in the human small intestine, commonly in the jejunum. Morphology Adult worm of T. saginata: The adult of T: saginata worm is opalescent white in color, ribbon-like, dorsoventrally flattened and segmented, measuring 5- 1 0 meters in length. The adult worm consists of head (scolex), neck and strobila (body). The general fea tures of adult worm are similar to any cyclophyllidean cestodes. Scolex: The scolex (head) of T. saginata is about 1-2 mm in diameter, quadrate in cross-section, bearing four hemispherical suckers situated at its four angles. They may be pigmented. The scolex has no rostellum or 1 booklets (which are present in T. solium). T. saginata is, therefore called the unarmed tapeworm. the suckers serve as the sole organ for attachment. the neck is long and narrow. The strobila (trunk) consists of 1,000-2,000 proglottids or segments- immature, mature and gravid. The gravid segments are nearly four times long as they are broad, about 20 mm long and 5 mm broad. The segment contains male and female reproductive structures. The testes are numerous, 300- 400 (twice as many as in T solium). The gravid segment has 15- 30 lateral branches. (as against 7-13 in T. solium). It differs from T: solium also in having a prominent vaginal sphincter and in lacking the accessory ovarian lobe. The common genital pore opens on the lateral wall of the segments. The gravid segments break away and are expelled singly, actively forcing their way out through the anal sphincter. As there is no uterine opening, the eggs escape from the uterus through its ruptured wall. Adult worm of T. solium: The adult worm is usually 2- 3 meters long. The scolex of T solium is small and globular about l mm in diameter, with four large cup-like suckers (0.5 mm in diameter), and a conspicuous rounded rostellum, armed with a double row of alternating round and small daggershaped hooks, 20- 50 in number. the neck is short and half as thick as the head. The proglottids number less than a 1,000. They resemble those of T. saginata in general. the gravid segments are twice as long as broad, 12 mm by 6 mm. The testes are composed of 150-200 follicles. there is an accessory lobe for the ovary. The vaginal sphincter is absent. The uterus has only 5-10 (under 13) thick lateral branches. A lateral thick-lipped genital pore is present, alternating between the right and left sides of adjacent segments. The gravid segments are not expelled singly, but pass passively out as short chains. The eggs escape from the ruptured wall of the uterus. 2 Eggs: Eggs of both species are indistinguishable. 1he egg is spherical, measuring 30- 40 mcm in diameter. lt has a thin hyaline embryonic membrane around it, which soon disappears after release. The inner embryophore is radially striated and is yellowbrown due to bile staining. In the center is a fully-developed embryo (oncosphere) with three pairs of hooklets (hexacanth embryo). The eggs do not float in saturated salt solution. the eggs of T. saginata are infective only to cattle and not to humans, whereas the eggs of T. solium are infective to pigs and humans too. Larva: The larval stage of Taenia is called as cysticercus. Cysticercus bovis is the larva ofT. saginata. Cysticercus cellulosae is the larva of T. solium. Cysticercus bovis: It is the larval form of T. saginala. the name cysticercus in derived from the Greek, kystisb/adder and kerkos- tail. The larva (cysticercus bovis) is infective stage for humans. the cysricercus is an ovoid, milky-white opalescent fluidfilled vesicle measuring about 5 mm x 10 mm in diameter, and contains a single invaginated scolex (bladder worm). the cysticerci are found in the muscles of mastication, cardiac muscles, diaphragm and tongue of infected cattle. They can be seen on visual inspection as shiny white dots in the infected beef (measly beef). Cysricercus bovis is unknown in humans. Cysticercus cellulosae: lt is the larval form of T. solium and also the infective form of the parasite. It can develop in various organs of pig as well as in man. the cysticercus cellulosae or "bladder worm" is ovoid opalescent milky-white, measuring 8-10 mm in breadth and 5 mm in length. The scolex of the larva, with its suckers, lies invaginated within the bladder and can be seen as a d1ick white spot. It remains viable for several months. Life Cycle of Taenia Saginata T. saginata passes its life cycle in two' hosts: 1. Definitive host: Humans are the definitive hosts and harbor the adult worm. 2. Intermediate host: Cattle (cow or buffalo) are the intermediate host and harbor the larval stage of the worm. Infective stage: Cysticercus bovis (larval stage) is the infective stage to man, while eggs are infective to cattle. the adult worm lives in the small intestine of man. The gravid segments from the adult worm break away and are expelled singly. They actively force their way out through the anal sphincter. 3 They are filtered out principally in the muscles, where they develop into the larval stage, cysticercus cellulosae in about 60-70 days. ln humans, it is a dead end and the larvae die without further development. Intestinal infection with T: solium occurs only in persons eating undercooked pork and usually in persons of low socioeconomic condition with poor sanitation. It is uncommon in Jews and Mohammedans, who are not generally pork eaters. But cysticercosis may occur in any person residing in endemic areas, even in vegetarians because the mode of infection is contamination of food or drink with egg deposited in soil. Eggs of T. solium are infective to pigs as well as to man. 4 Pathogenicity and Clinical Features : Intestinal taeniasis: It can be caused by both T. saginata and T solium. The adult worm, in spite of its large size, causes surprisingly little inconvenience to the patient. When the infection is symptomatic, vague abdominal discomfort, indigestion, nausea, diarrhea and weight loss may be present. Occasional cases or acute intestinal obstruction, acute appendicitis and pancreatitis have also been reported. Cysticercosis: It is caused by larval stage (cysticercus cellulosae) of T. solium.  Cysticercus cellulosae may be solitary or more often multiple.  Any organ or tissue may be involved, the most common being subcutaneous tissues and muscles. It may also affect the eyes, brain, and less often the heart, liver, lungs, abdominal cavity and spinal cord.  The cysticercus is surrounded by a fibrous capsule except in the eye and ventricles of rhe brain.  The larvae evoke a cellular reaction starting with infiltration of neutrophils, eosinophils, lymphocytes, plasma cells, and at times, giant cells. This is followed by fibrosis and death of the larva with eventual calcification.  The clinical features depend on the site affected: - Subcutaneous nodules are mostly asymptomatic.  Muscular cystlcercosis may cause acute myositis.  Neurocysticercosis (cysticercosis of brain) is the most common and most serious form of cysticercosis. About 70% of adult-onset epilepsy is due to neurocysticercosis. Other clinical features of neurocysticercosis are increased intracranial tension, hydrocephalus, psychiatric disturbances, meningoencephalitis, transient paresis, behavioral disorders, aphasia and visual disturbances. 1t is considered as the second most common cause of intracranial space occupying lesion (lCSOL) after tuberculosis in India.  - In ocular cysticercosis, cysts are found in vitreous humor, subretinal space and conjunctiva. The condition may present as blurred vision or loss of vision, iritis, uveitis and palpebral conjunctivitis. Laboratory Diagnosis Stool examination: Eggs: Microscopic examination of feces shows characteristic eggs of Taenia in 20- 80% of patients. Formol- ether sedimentation method of stool concentration is useful. Eggs can also be detected by cellophane swab method (NIH swab) in 85-95% patients. Species identification cannot be made from the eggs, since the eggs of T. saginata and T. solium are similar. 5 Proglottids: Species identification can be done by examining with a hand lens, the gravid proglortid pressed between two slides, when branching can be made out (15- 20 lateral branches in T. saginata; under 13 in T. solium). Scolex: Definitive diagnosis can also be established by demonstration of unarmed scolex in case of T. saginata after anthelmintic treatment. Detection of Taenia antigen in feces: Antigen capture enzyme-linked immunosorbenl assay (ELISA) using polyclonal antisera against Taenia are employed to detect coproantigen in feces since 1990 and is more sensitive than microscopy (specificity 100% and sensitivity 98%). The drawback of the test is that it cannot differentiate between T. saginata and T.solium. Serodiagnosis: Specific antibodies to adult stage antigen in se rum can be demonstrated by ELISA, indirect immunofluorescence test and indirect hemagglutination (IHA) test. Molecular diagnosis: Both deoxyribonucleic acid (DA) probes and polymerase chain reaction (PCR) technique are used to detect and differentiate between eggs and proglottids of T. saginata and T. solium. Laboratory Diagnosis of Cysticercosis: Diagnosis of cysticercosis is based on the following. Biopsy: Definitive diagnosis of cysticercosis is by biopsy of the lesion and its microscopic examination to show the invaginated scolex with suckers and hooks. Imaging methods: - X-ra.y: , Computed tomography (CT) scan of brain , - Magnetic resonance imaging (MRI) scan of the brain Serology: - Antibody detection: Anticysticercus antibodies in serum or cerebrospinal fluid (CSF) can be detected by "ELISA" and enzyme-linked immunoelectrotrasfer blot (EITB) tests. Antigen detection: Antigen can be detected in serum and CSF by ELISA, using monoclonal antibodies and indicate recent infection. Prophylaxis  Beef and pork to be eaten by man should be subjected to effective inspection for cysticerci in slaughter house.  Avoidance of eating raw or undercooked beef and pork. The critical thermal point of cysticercus is 56°C for 5 minutes.  Maintenance of clean personal habits and general sanitary measures.  For control of cysticercosis, prevention of fecal contamination of soil, proper disposal of sewage and avoidance of eating raw vegetables grown in polluted soil are useful measures.  Detection and treatment of persons harboring adult worm, as they can develop cysticercosis due to autoinfection. 6 Hymenolepis nana: Common Name: Dwarf tapeworm. History and Distribution : The name Hymenolepis refers to the thin membrane covering the egg (Greek hymen- membrane, lepis-rind or covering) and nana to its small size (nanus-dwarf). It was first discovered by Bilharz in 1857.  It is cosmopolitan in distribution bur is more common in warm than in cold climates.  Infection is most common in school children and institutional populations.  Hymenolepis nana is the smallest and the most common tapeworm found in the human intestine. It is unique that it is the only cestode which completes its life cycle in one host- humans. Habitat : The adult worm lives in the proximal ileum of man. H. nana is found in rodents like mice and rats, where they are found in the posterior part of the ileum. Morphology: Adult worm: H. nana is the smallest intestinal cestoda that infects man.  It is 5- 45 mm in length and less than l mm thick. The scolex has four suckers and a retractile rostellum with a single row of hooklets.  The long slender neck is followed by the strobila consisting of 200 or more proglottids, which are much broader than long.  Genital pores are situated on the same side along the margins.  The uterus has lobulated walls and the testis is round and three in nwnber. Eggs are released in the intestine by disintegration of the distal gravid segments. Egg: The egg is roughly spherical or ovoid, 30-40 µmin size.  It has a thin colorless outer membrane and inner embryo where enclosing the hexacanth oncosphere.  The space between two membranes contains yolk granules and 4-8 thread like polar.filaments arising from two knobs on the embryophore.  The eggs float in saturated solution of salt and are non bile stained.  They are immediately infective and unable to survive for more than 10 days in external environment. 7 Life Cycle: Mode of transmission:  Infection occurs by ingestion of the food and water contaminated with eggs. Internal autoinfection may also occur when the eggs released in the intestine hatch there itself.  External autoinfection occurs when a person ingest own eggs by fecal oral route. H. nana is unusual in that it undergoes multiplication in the body of the definitive host. When the eggs are swallowed, or in internal autoinfection, they hatch in the small intestine. the hexacanth embryo penetrates the intestinal villus and develops into the cysticercoid larva.  This is a solid pyriform structure, with the vesicular anterior end containing th e invaginated scolex and a short conical posterior end.  After about 4 days, the mature larva emerging out of the villus evaginates its scolex and attaches to the mucosae.  It starts strobilization, to become the mature worm, which begins producing eggs in about 25 days. A different strain of H. nana infects rats and mice. The eggs passed in rodent feces are ingested by rat fleas (Xenopsylla cheopis and others), which acts as the intermediate host. The eggs develop into cysticercoid larvae in the hemocele of these insects. Rodents get infected when they eat these insects. The murine strain does not appear to infect man. 8  However, the human strain may infect rodents, which may, therefore, constitute a subsidiary reservoir of infection for the human parasite. Clinical Features: Hymenolepiasis occurs more commonly in children. There are usually no symptoms but in heavy infections, there is nausea, anorexia, abdominal pain, diarrhea and irritability. Sometimes pruritus may occur due to an allergic response. Laboratory Diagnosis: The diagnosis is made by demonstration of characteristic eggs in feces by direct microscopy. Concentration methods like salt flotation and formalin ether may be readily used. ELiSA test has been developed with 80% sensitivity. Treatment: Praziquantel (single dose of 25 mg/kg) is the drug of choice, since it acts both against the adult worms and the cysticercoids in the intestinal villi. Nitazoxanide 500 mg BD for 3 days may be used as alternative. Prophylaxis: Maintenance of good personal hygiene and sanitary improvements. Avoiding of consumption of contaminated food and water. 9  Rodent control. Dipylidium Caninum: This common tapeworm of dogs and cats, it may accidentally cause human infection, mainly in children. Morphology : The adult worm in the intestine is about l 0-70 cm long. The scolex has four prominent suckers and a retractile rostellum with up to seven rows of spines. The mature proglortid has two genital pores, one on either side, hence the name Dipylidium (dipylos-two entrances). Gravid proglottids are passed out of the anus of the host singly or in groups. Life Cycle : Definitive host: Dogs, cats and rarely man. Intermediate host: Fleas  Man acquires infection by ingestion of flea harboring cysticercoid larva.  the eggs or proglottids passed in feces of dogs and cats are eaten by larval stages of dog and cat fleas, Ctenocephalides canis and C.felis.  The embryo develops into a tailed cysticercoid larva.  When the adult fleas containing the larvae are eaten by dogs, cats, or rarely humans, infection is transmitted. Clinical Features :Human infection is generally asymptomatic, but the actively motile proglottids passed in stool may raise an alarm. Diagnosis: the diagnosis is made by detection of proglortids or eggs in stool. Treatment: the drug of choice is praziquantel. 10 Class : Cestoda Order: pseudophyllidea 1- The member of this order have an elongated head with two slit – like sucking grooves. 2- egg are operculated. they develop and hatch in water to produce a ciliated embryo. 3- they require two intermediate hosts. Diphyllobothrium latum : (Broad Tapeworm, Fish Tapeworm) Causative agent of diphyllobothriasis. This tapeworm is endemic in lake regions in Europe , Asia, and America and parasitizes in the small intestine of humans and fish-eating mammals such as pigs, dogs, and cats. Common Name Fish tapeworm/ Broad tapeworm. History and Distribution The head of the worm was found by Bonnet in 1777, and its life cycle was worked out by Janicki and Rosen in 1917. Diphyllobothriasis (infection with Diphyllobothrium) occurs in Central and northern Europe, particularly in the Scandinavian countries. It is also found in Siberia, Japan, north America and Central Africa. In countries like India, where fish is eaten only after cooking, the infection does not occur.  Longest cestode infecting man: Diphyllobothrium latum 11   Smallest cestode infecting man: Hymenolepis nana. Habitat: The adult worm is found in the small intestine, usually in the ileum, where it lies folded in several loops with the scolex embedded in the mucosa. Morphology : Adull worm: It is ivory-colored and very long, measuring up to 10 meters or more. It is the largest tapeworm inhabiting the small intestine of man.  As in all cestodes, the adult worm has three parts: (1) scolex, (2) neck and (3) strobila. Scolex(head) is spatulate or spoon-shaped, about 2-3 mm long and l mm broad. It carries two slit-like longitudinal sucking grooves (bothria), one dorsal and the other ventral. the scolex lacks suckers and hooks.  eek is thin, unsegmented and is much more longer than the head.  Strobila consists of 3,000-4,000 proglottids, consisting of immature, mature and gravid segments in that order from front to backwards.  The mature proglottid is broader than long, about 2-4 mm long and l 0-20 mm broad and is practically filled with male and female reproductive organs (Fig. 3B).  The testes are represented by numerous minute follicles situated laterally in the dorsal plane.  The female reproductive organs are arranged along the midline, lying ventrally. The ovary is bilobed. The large rosette-like uterus Lies convoluted in the center. 1hree genital openings are present ventrally along the midline-the openings of the vas deferens, vagina and uterus in that order, from front to backwards.  The fertilized ova develop in the uterus and are discharged periodically through the uterine pore.  The terminal segments become dried up after delivering many eggs and are discharged in strands of varying lengths in the feces. 12 Egg:  D. latum is a prolific egg layer and a single worm may pass about a million eggs in a day.  Egg is broadly ovoid, about 65 µm by 45 µm, with a thick, light brown shell.  It has an operculum at one end and often a small knob at the other.  The egg does not float in saturated salt solution and is bile stained.  They are not infective to humans. Larval stages: There are three stages of larval development: 1. l. First stage larva (coracidium) 2. Second stage larva (procercoid) 3. Third stage larva (plerocercoid). Life Cycle Definitive hosts: Man, dog and cat. Man is the optimal host. First intermediate host: Freshwater copepod, mainly of genera Cyclops. Second intermediate host: Freshwater fish (salmon, trout, etc.). infective form to human: Third stage plerocercoid larva.  The adult worm lives in the small intestine. It lays operculated eggs which are passed along with the feces in water.  The freshly-passed egg contains an immature embryo surrounded by yolk granules. The embryo with six hooklets (hexacanth embryo) inside the egg is called the oncosphere.  In water, it matures in about l 0- 15 days and ciliated first stage larva, called coracidium emerges through the operculum.  Coracidium (first stage larva) can survive in water for about 12 hours, by which time it should be ingested by the fresh water crustacean copepod Cyclops, which is the first intermediate host (Fig. 5). 13  In the midgut of the Cyclops, the coracidium casts off its ciliated coat and by means of its six hooklets, penetrates into the hemocele (body cavity). In about 3 weeks, it becomes transformed into the elongated second stage larva about 550 µm long, which is called the procercoid larva.  Procerco id larva has a rounded caudal appendage (cercomer) which bears the now useless hooklets.  If the infected Cyclops is now eaten by a freshwater fish (second in termediate host), the procercoid larva penetrates the intestine of the fish and grows. In the fish, procercoid larva looses its caudal appendage and develops into the third stage larva called the plerocercoid larva or sparganum (Fig. 5).  Plerocercoid larva has a glistening white flattened unsegmented vermicule, with a wrinkled surface, is about 1-2 cm long, a nd possesses rudimentary scolex. lhis is the stage infective for humans. Man gets infection by eating raw or undercooked fish containing plerocercoid larva.  The larva develops into adult worm in the small intestine.  The worm atta ins maturity in about 5-6 weeks and starts laying eggs, which are passed along with the feces. The cycle is thus repeated. The adult worm may Live for about 10 years or more. 14 Pathogenicity and Clinical Features : The pathogenic effects of diphyllobothriasis depend on the mass of the worm, absorption of its by products by the host and deprivation of the host's essential metabolic intermediates.  In some persons, infection may be entirely asymptomatic, while in others there may be an evidence of mechanical obstruction.  Transient abdominal discomfort, diarrhea, nausea, weakness, weight loss and anemia are the usual manifestations. Patients may be frightened by noticing the strands of proglottids passed in their feces.  A kind of pernicious anemia, sometimes caused by the infection, is called bothriocephalus anemia. This was formerly believed to be racially determined, being common in Finland and rare elsewhere. The anemia develops because the tapeworm absorbs large quantity of vitamin B12 and interferes with its ileal absorption, leading to vitamin B 12 deficiency.  In severe cases, patients may exhibit neurologic sequelae of vitamin B 12 deficiency. Laboratory Diagnosis: Stool microscopy: Eggs are passed in very large number in feces, and therefore, their demonstration in feces offers an easy method of diagnosis. The proglottids passed in feces can also be identified by their morphology. Serodiagnosis: A coproantigen detection test is available to diagnose diphyllobothriasis. Treatment  Praziquantel in a single dose of 10 mg/ kg is effective.  Parenteral vitamin B12 should be given, if B12 deficiency Prophylaxis : Infection can be prevented by:  Proper cooking of fish.  Deep freezing (- 10°C for 24-48 hours) of fish, if it is to be consumed raw. Prevention of fecal pollution of natural waters.  Periodical deworming of pet dogs and cats. 15 Sparganosis Sparganosis is caused by the extra intestinal presence in the human body of larvae of human ( Diphyllobothrium latum ). Pathology and clinical features : Infestation with living larvae causes a painful oedematous reaction. dead larvae cause intense locally inflammatory reactions. there are numerous eosinophils and there can be abscess formation. there can be ocular sparganosis in the soft tissue near the eye, resulting in sever damage. invasion of CNS may occur. Diagnosis : Examination of biopsy materials or excited larva in infected tissue. GOOOOOOOOOD LUCK ……..Prof. AMAL KH. KH. 16