Parasitology Past Paper PDF

Revision Types of hosts:  Definitive host: it is the host that harbors the adult (mature) stage of the parasite.  Intermediate host: it is the host that harbors the immature larval stage of the parasite.  Reservoir host: it is an animal that harbors the mature stage of the parasite.  Vector:...

Revision Types of hosts:  Definitive host: it is the host that harbors the adult (mature) stage of the parasite.  Intermediate host: it is the host that harbors the immature larval stage of the parasite.  Reservoir host: it is an animal that harbors the mature stage of the parasite.  Vector: an arthropod which carries the parasite from one host to another host. Types of parasites  Ectoparasite: They inhabit the surface of the body of the host without penetrating into the tissues. The infection by these parasites is called infestation,  Endoparasite: They live within the body of the host. Invasion by the endoparasite is called infection.  Temporary parasite: visits the host to take its blood meal.  Permanent parasite: lives in or on the host the whole of its life.  Facultative parasite: lives as parasite or free living.  Obligatory parasite: can"t live without it"s host.  Specific parasite: affects one specific particular host.  Nonspecific parasite: normally it inhabits and completes its life cycle in an animal host but can inhabit a human host without completing its life cycle.  Opportunistic parasite: it can cause disease only in immunodeficient individuals, while no symptoms appear in immunocompetent individuals. Fasciola  Disease: Fascioliasis.  Habitat: Bile ducts of the liver and gall bladder.  Definitive host: Herbivorous animals most commonly, sheep, cattle, goats, 1  Camels, and buffalo. Man can be occasionally infected.  Intermediate host: Snails Lymnaea cailliaudi and Lymnaea truncatula. Egg in stool: (Diagnostic stage) Size: 150 x 90 um. Shape: ovoid. Shell: thin, operculated. Color: bile stained (yellowish brown). Content: embryonic cells (immature). Encysted metacercaria (Infective stage):  Size: 0.25 mm diameter.  Shape: spherical with a thick white cyst wall. Mode of infection  Infection occurs by eating contaminated vegetation or drinking water with metacercaria. Clinical picture: Acute phase: patients may develop symptoms like prolonged febrile illness, anorexia, and right upper quadrant abdominal pain. Chronic phase: Patients may develop symptoms of biliary obstruction such as biliary colic, epigastric pain, and jaundice, and right upper quadrant abdominal tenderness, anemia. Laboratory diagnosis: A. Stool examination: detecting parasitic eggs is confirmatory B. Serological tests: for antibody and antigen detection are of value during the migratory stage of the worms and ectopic infection. C. Eosinophilia. D. Ultrasound and CT. D. Molecular diagnosis: A nested-PCR was developed for detection of parasitic DNA in human stool and urine samples. 2  Treatment:  Biothionol Triclabendazole Prevention and control:  Mass drug administration  Health education.  Snail control. Heterophyes heterophyes  Habitat: Small intestine.  Definitive Host: Man- & fish-eating animals (dogs & cats).  Intermediate Host: 1st intermediate host: Pirenella conica snail. 2nd intermediate host: boury & bolty fish.  Infective stage: Encysted metacercaria  Diagnostic stage: Egg in stool.  Diagnostic stage (Egg):  Size: 30 μm ×15 μm.  Shape: oval.  Shell: thick double walled with operculum & posterior knob.  Color: brownish yellow.  Content: miracidium (mature). Mode of infection  Man and fish-eating animals are infected by eating raw, undercooked, or under-salted fish (feseekh) for less than 10 days containing encysted metacercaria (the infective stage). 3  Clinical Picture: Most infections are asymptomatic or accompanied by mild intestinal discomfort, which may include mucous diarrhoea, colicky pains. Laboratory diagnosis: Direct Microscopic examination: The diagnosis is suggested by detecting the characteristic eggs in the stool Treatment: Praziquantel Prevention and control:  Proper cooking of fish and salting not less than 10 days.  Snail control. Schistosomes S. haematobium S. mansoni D.H Man Man R.H Only man Primates such as rats I.H (snail) Bulinus Biomphalaria The vesical, prostatic, Small branches of the inferior Habitat and uterine plexuses. mesenteric vein in the region of the lower colon. Egg - Shape - Size (µm) Oval Oval - 150x 60 140x 60 - Shell (spine) - Color Thin (terminal) Thin (lateral) - Translucent Yellowish brown Content - Secreted in: Miracidium Miracidium - Urine Stool 4   Infective stage: Cercariae.  Diagnostic stage: Eggs in urine in Schistosoma hematobium, eggs in stool in Schistosoma mansoni. Cercaria (the infective stage):  Cercaria consists of a body with glands, which is used to penetrate skin and forked tail  Mode of infection Humans become infected by penetration of cercariae through intact skin on coming in contact with water (skin penetration) Clinical picture 1-Stage of migration: lung: irritation and minute haemorrhage, cough, sputum, dyspnea and eosinophilia (verminous pneumonia). 2-Due to escape of eggs in urine in case of Schistosoma haematobium:  Burning sensation during micturition, suprapubic pain, terminal haematuria, and frequency of micturition. 3- Due to scape of eggs in stool in case of Schistosoma mansoni:  Abdominal pain, frequent motion, dysentery with blood and mucus in stools. Laboratory diagnosis:  Direct diagnostic methods  Egg detection in stool or urine.  Egg hatching (egg viability test  Rectal biopsy (rectal snip) in S. mansoni. 5   Bladder biopsy: by using cystoscope in S.hematobium.  Indirect:  Eosinophilia, anaemia.  Sero-diagnostic methods: ELISA Treatment of Schistosomes  Praziquantel: It is the drug of choice for schistosomiasis and is effective against all Schistosoma species that infect humans. Prevention and control  Sanitary water supply.  Snail control  Health education. Taenia saginata ) beef tapeworm)  Habitat: Upper third of small intestine.  Definitive hosts: Man is the only definitive host.  Intermediate hosts: Cattle.  Diagnostic stage: Eggs, gravid segment  Infective stage: cysticercus bovis Gravid segments:  Narrower and longer than mature segments.  Uterine branches are between 15 and 20 branches, with an average of 18. Eggs: (Diagnostic stage)  Size: 28-40 μm.  Shape: spherical.  Shell: thick on which distinct radial striations reside. 6  Colour: yellowish brown.  Content: mature i.e., hexacanth embryo with three pairs of hooklets Larva (cysticercus bovis (Infective stage)  Size: 5-10 mm in diameter  Shape: translucent fluid-filled bladder with an invaginated scolex.  Mode of infection Humans are infected by ingesting raw or undercooked beef infected with cysticercus bovis. Clinical picture: 1. Symptoms of irritable bowel, particularly abdominal pain. Also, nausea, distension and anorexia, diarrhea, or constipation. 2. The most specific complaint is the discomfort and anal pruritus (perianal itching) caused by the proglottids independently crawling out of the anus. 3. Intestinal obstruction. Laboratory diagnosis:  Stool examination for egg detection.  The perianal swab method may also be effective to detect proglottids.  Antigen detection by ELISA. Treatment: Praziquantel. Niclosamide. Prevention and control:  Beef inspection for the presence of cysticerci.  Beef must be thoroughly cooked, especially in areas of endemicity, to at least 56 °C internal temperature. 7  Freezing at –10 °C for 10 days is usually lethal to Taenia cysticerci, but they can withstand 70 days at 0 °C. Taenia solium (Pork tapeworm)  Habitat: small intestine.  Definitive host: Humans.  Intermediate host: Pigs in taeniasis and man in cysticercosis  Segments: The gravid segments’ number of lateral uterine branches is between 7 and 13 branches.  source of infection: pigs Eggs (Diagnostic and infective stage):  The eggs of T. solium and T. Saginata are indistinguishable by standard parasitology procedure. The larva (cysticercus cellulosa) (Infective stage):  Similar to T. Saginata but the scolex is hooked. Diagnosis: similar to T. saginata.  The eggs of T. solium and T. Saginata can be distinguished by Ziehl-Neelsen staining or using molecular techniques.  The species can be also distinguished by a passed gravid proglottids based on the number of uterine branches. Treatment:  Similar to T. saginata but Niclosamide treatment is contraindicated because it causes disintegration of the worm in the small intestine. This increases the risk of autoinfection. Hymenolepis nana (Dwarf tapworm) 8   Geographical distribution: H. nana is the most common tapeworm of humans in the world, especially in children.  Habitat: small intestine.  Definitive hosts: Man.  Intermediate host; Man & sometimes flea larva  Reservoir hosts: Rats.  Diagnostic stage: Eggs and gravid segment.  Infective stage: Egg and cysticercoid nana.  Eggs: - Size: 35:45 µm. - Shape: rounded or spheroid. - Shell: 2 layers with polar thickenings and numerous polar filaments originate from the polar thickenings. - Color: colorless. - Contents: Three pairs of hooklets; hexacanth embryo (onchosp here) - Larval stage: Cysticercoid nana. - Shape: Oval cyst containing fluid. - Scolex: Upright in position, carrying suckers & hooks. - Tail: Posterior (Cercocystic cysticercoid). - Mode of infection: - Accidental ingestion of eggs: by ingesting fecally contaminated foods or water, touching your mouth with contaminated fingers or by ingesting contaminated soil. - Autoinfection: Internal and external - Clinical Symptoms: 9 - Symptomatic: Heavy H. nana infections often develop gastrointestinal symptoms, such as abdominal pain, anorexia, diarrhea, dizziness, and headache. - Laboratory diagnosis: - Stool analysis: is made by demonstration of characteristic eggs in feces by direct microscopy. - ELISA test has been developed with 80% sensitivity. - Treatment: - Praziquantel is considered to be the treatment of choice for infections with H. nana. - Niclosamide is also known to be an effective alternative medication - Prevention and Control: - Wash your hands with soap and warm water after using the toilet, changing diapers, and before preparing foods. - Insect control - Public health and sanitation programs, limination of rats help prevent the spread of hymenolepiasis - Health education Hymenolepis diminuta (Rat tapeworm)  Habitat: Small intestine  Definitive host: Rat, mice and rarely human.  Intermediate host: Rat flea larva  The Infective stage: cercocystic cysticercoid larva  Diagnostic stage: The characteristic eggs and gravid segments Eggs: Size: 55: 70 µm Shape: oval 10  Shell: surrounds the embryo with distinct two polar thickenings and no polar filaments. Content: The hexacanth embryo contains three pairs of hooks. Color: brownish Clinical Symptoms:  Symptomatic: (Hymenolepiasis diminuta): In heavy infection with H. diminuta there mild symptoms such as diarrhea, nausea, abdominal pains, and anorexia. Treatment: Praziquantel. Niclosamide. Echinococcus granulosus (Hydatid worm) Definitive hosts: Dogs, foxes and wolves. Intermediate host; Man & cattle, pigs, sheep Infective stage: Egg Diagnostic stage: hydatid cyst  Egg:  Size: 28-40 μm.  Shape: spherical.  Shell: thick on which distinct radial striations reside.  Colour: yellowish brown.  Content: mature i.e., hexacanth embryo with three pairs of hooklets Hydatid disease 11  Definition: it is a pathological condition where human tissues carry the hydatid cyst (the larval stage of Echinococcus granulosus) where man acts as the intermediate host of the parasite. Mode of infection:  Ingestion of contaminated food and drinks by Echinococcus granulossus eggs by the following ways:  Handling infected dogs where the hairs are usually contaminated with eggs Hydatid cyst:  Size: 1-10 cm.  Shape: Spherical. The wall of the cyst has 2 layers: ,  Outer laminated non-cellular layer.  Inner cellular germinal layer Contents:  (a) scolices  (b) Brood capsules: cysts formed by invagination of the germinal layer from which scolices develop.  (c) Daughter cysts: cysts formed of the 2 layers of the mother cyst, giving rise to scolices, brood capsules and even grand¬daughter cysts.  (d) Hydatid fluid.  Clinical picture:  Large sized cysts cause pressure atrophy of the affected organs.  The most common affected organs are Liver (70%) and lung (20%).  Other organs such as brain, bone, spleen, kidney, muscles, heart and eye (10%) Complications  Spontaneous rupture of cysts leads to severe allergic reactions (anaphylactic shock)  Bacterial infection can occur leading to abscess formation. 12   Diagnosis:  Ultrasound.  Scolicices in sputum or urine.  Puncture or aspiration of hydatid fluid.  Intradermal test (Casoni test). Treatment: Surgical removal of the cyst. Albendazole in inoperable cases and after surgery Prevention and control: Avoid contamination of food with dog faeces Periodic examination and treatment of pet dogs Infected organs in slatter houses should be destroyed. Ascaris lumbricoides  Habitat: small intestine.  Definitive hosts: Man.  Intermediate host; there is no intermediate host.  Diagnostic stage: Immature egg in stool  Infective stage: Egg containing second stage rhabditiform larva. Eggs: Size: an average size 60× 45μm. Shape: broad oval in shape. Shell: is thick: The outer layer is a course mammillated coat. Color: golden brown in color, (bile stained). Content: The content is a fertilized ovum.  Mode of infection: 13   Swallowing the infected egg of Ascaris containing the infective second stage rhabditiform larva with contaminated food and water.  Children playing about in mud can transmit eggs to their mouth through dirty fingers.  Clinical picture: A-migratory phase:  The migrating larvae through the lung may cause verminous pneumonia. B- Intestinal ascariasis is manifested by: Nausea, Vomiting, and Colicky abdominal pain. Weight loss and diarrhea. Malabsorption of nutrition and growth retardation.  Complications: Intestinal obstruction, Hepatic abscesses, acute pancreatitis. Acute appendicitis. Laboratory diagnosis:  Direct: Detection of eggs in feces by: stool examination Seeing the worms in the intestines by: Endoscopy and X-ray photographs Seeing worms after they are expelled naturally in stool.  Indirect: ELISA, esinophilia Treatment:  Albendazole. Mebendazole. Prevention and control:  Providing clean drinking water.  Washing vegetables with water. Trichuris trichiura (Whip worm)  Habitat: large intestine (mainly caecum).  Definitive Host: Humans. 14  Intermediate Host: No intermediate host.  Diagnostic stage: Immature eggs.  Infective stage: Eggs containing first stage larva Eggs (diagnostic stage):  Size: 50 x 25 μm.  Shape: barrel shaped  Shell: triple shell with a projecting mucus plug at each pole.  Color: brown but the plugs are colorless.  Content: immature (single ovum). Mode of infection: Human infection occurs when the mature embryonated eggs containing the infective 1st stage rhabditiform larvae are swallowed in contaminated food or water. Clinical Picture: Severe infection may lead to diarrhea dysentery, profuse bloody diarrhea, cramps, tenesmus. Complications  Trichuris may also cause rectal prolapse in children with heavy infections.  Anemia is a common finding, either microcytic hypochromic anemia due to continuous blood loss or hyperchromic pernicious anemia due to toxin production.  Worms may occasionally migrate to the appendix, causing appendicitis  Laboratory Diagnosis:  Stool Examination: for detection of eggs.  Blood Examination: eosinophilia.  Treatment: 1-Mebendazole 2-Albendazole  Prevention and control: 15   Avoid consumption of unwashed fruits and vegetables and proper washing of green vegetables.  Pure water supply.  Fly control. Ancylostoma duodenale  Habitat: Small intestines, mostly the jejunum.  Definitive host: Man (the only natural host).  Intermediate host: No intermediate host.  Diagnostic stage :immature eggs.  Infective stage: Third stage filariform larva.  Eggs (diagnostic stage):  Size: 60 x 40 μm.  Shape: Oval.  Shell: Thin. There is a clear space between the segmented ovum and eggshell.  Color: translucent.  Content: Freshly laid eggs contain a developing embryo in the early stages of cleavage (4- 8 cells).  The 3rd stage filariform larva (infective stage): 500- 700 µm long, Sheathed, Sharply pointed tail.  Mode of infection  Active penetration of 3rd stage filariform larvae to his exposed skin (especially hands, feet, arms, and legs).  Disease: Ancylostomiasis.  The pulmonary stage: Larval migration through lung tissue causes a pulmonary hypersensitive response called (verminous pneumonia)  The intestinal stage: 16   The adult worms cause mechanical injury to the mucosa by their buccal capsule and teeth during their blood meal. Complications  Hypoproteinemia: which leads to malnutrition  Iron deficiency anemia due to blood loss.  Diagnosis : Stool examination: to detect eggs. Stool culture: to detect 3rd stage filariform larva.  Treatment:  Albendazole, Mebendazole.  Iron supplement,High protein diet and vitamin.  Prevention and control:  Wear shoes, gloves and avoid walking bare footed.  Avoid using fertilizer made from human feces. Trichinella spiralis  Habitat: Small intestine.  Definitive host: Man, rats and pigs  Intermediate host: Man, rats and pigs.  Diagnostic stage: adults, larvae, and muscle encysted larvae.  Infective stage: Trichina capsule (encysted Trichinella larva)  Encysted larvae:  An ellipsoidal lemon shaped  Sheath develops as a result of host-tissue interaction around the tightly coiled larva.  Found in the striated muscles of the host. 17  Mode of infection: Human infection occurs by eating raw or inadequately cooked meat containing viable larvae.  Clinical picture: Trichinosis, Trichinellosis.  The intestinal phase: Common symptoms include anorexia, nausea, vomiting, diarrhea, or constipation.  The invasive phase:  Severe myalgia is experienced.  Periorbital, and subconjunctival hemorrhages.  Splinter hemorrhages and retinal hemorrhages.  Laboratory diagnosis:  Direct diagnosis  Stool examination: Larvae or adult worms are rarely seen in fecal samples during the intestinal phase.  Muscle biopsy: confirms diagnosis by detection of the encysted T. spiralis larvae. Indirect diagnosis  Intradermal test (Bachman test): a skin test for trichinosis in which an extract of Trichinella larvae is injected intradermally. Treatment:  Albendazole. Mebendazole or thiabendazole. Steroids to decrease inflammation.  Prevention and control:  Adequate cooking and freezing of meat prevent human infection by T. spiralis.  Eradication of rats.  Proper inspection of meat at slaughterhouses. Enterobius vermicularis (Oxyuris vermicularis, Pinworm)  Habitat: large intestine. 18  Definitive Host: Man.  Intermediate Host: no intermediate host.  Diagnostic stage: eggs and adult worms.  Infective stage: eggs.  Eggs (diagnostic and infective stage):  Size: 50 x 20 μm.  Shape: elongated ovoid, straight on one side, and convex on the other (planoconvex).  Shell: has D- shaped shell double-layered  Color: translucent.  Contents: mature (larva).  Clinical Picture: Enterobiasis or Oxyurisasis.  pruritus ani caused by the migration of the female worms from the anus onto the perianal skin for egg deposition at night this cause sleep disturbances with subsequent nervousness, insomnia, and restlessness. Nocturnal enuresis may occur.  Urinary tract infection and vulvovaginitis.  Acute appendicitis.  Man acquires infection via one of the following:  Self-inoculation (transferring eggs to the mouth with hands). i.e., autoinfection.  Through exposure to eggs in the environment (e.g., contaminated surfaces, clothes, bed linens, etc.).  Lab diagnosis  Detection of Eggs by:  NIH Swab Method: The NIH swab (National Institutes of Health) has been widely used for the collection of specimens. It consists of a glass rod at one end of which a piece of transparent cellophane is attached with a rubber band.  Scotch adhesive tape swab: 19   A piece of sticky surface tape is applied to the perianal skin. The tape is transferred to a glass slide, sticky side down and examined under the microscope. Swabs should be taken in the morning before defecation or bathing.  Detection of eggs in stool: eggs can be detected in faeces in a small proportion of patients.  Nail examination: The eggs may be demonstrated in the dirt collected from beneath the fingernails of infected children.  Urine examination for eggs.  Treatment: It is recommended that all household members be treated at the same time.  Albendazole, Mebendazole  White precipitate ointment to the perianal area to relief inflammation and itching. Wuchereria bancrofti  Habitat: adults live in the lymphatic system.  Definitive host: Man.  Vectors (intermediate host): Culex, Anopheles and Aedes.  Microfilaria diagnostic stage:  Measures 250-300 µm in length, Has a fine sheath, the body cavity is nucleated except for the tail (the tail is free of nuclei a determining feature), and the posterior end tapers into a point, while the anterior end is blunt.found in blood at night  3rd stage Larvae: Found in the vector, the infective stage. It between 1500-2000 µm lengths. One microfilaria produces one third-stage larva.  Microfilarial periodicity: It is the time of day when filarial microfilariae are mostly prevalent in the peripheral blood.  Nocturnal periodicity: The highest level of blood microfilariae is in the night between 10 pm and 2-4 am.  Laboratory diagnosis: - 20  CBC (Complete Blood Count): hypereosinophilia.  Detection of microfilariae (diagnostic stage) in blood specimen: Blood is drawn between 10 p.m. and 4 a.m.  Blood film: Making thin and thick blood film that are stained with Giemsa or haematoxylin stain.  Detection of adult worms in the lymphatic vessels: By ultrasonography 21