Home

About Medical Parasitology

New Infections

Ova & Parasite (O&P) Exams

New CPT Codes

Quizzes

Review Tests

FAQ

Information Tables

Organism Index (A-Z)

Parasitology Exam (HELMINTHS)

***Reminder: Slides and examination questions are copyrighted and cannot be copiedfor publication.

1. The incorrect match between organism and the appropriate diagnostic

procedure is: a. Onchocerca volvulus - examination of skin snips b. Cryptosporidium - modified acid fast stain c. Echinococcus granulosus - routine ova and parasite examination d. Schistosoma haematobium -- examination of urine sediment ANSWER (c): The appropriate procedure for the diagnosis of Echinococcus granulosus(hydatid disease) would involve the microscopic examination of hydatid fluid aspiratedfrom a cyst. Immature scolices and/or hooklets would be found in the centrifuged fluidsediment and could be identified under the microscope. 2. Charcot-Leyden crystals in stool may be associated with an immune response

and are thought to be the breakdown products of: a. neutrophils b. eosinophils c. monocytes d. lymphocytes ANSWER (b): When eosinophils disintegrate, the granules reform into Charcot-Leydencrystals. Eosinophils are more likely to be present in patients with helminth infections(rather than protozoa). 3. Morphological characteristics of the rhabditiform (non-infective) larvae of

Strongyloides stercoralis are: a. a short buccal capsule and large genital primordium b. a long buccal capsule and pointed tail c. a short buccal capsule and small genital primordium d. a small genital primordium and notch in tail ANSWER (a): The rhabditiform larvae of Strongyloides stercoralis are characterized bythe short buccal capsule (mouth) and large genital primordium; these hookwormlarvae have a long buccal capsule and very small genital primordium. 4. Visceral and ocular larva migrans are associated with which of the following

organisms and diagnostic test? a. Toxocara - serology b. Onchocerca - skin snips c. Dracunculus - skin biopsy d. Angiostrongylus - CSF examination ANSWER (a): Toxocara spp. cause visceral and/or ocular larva migrans, which occurswhen humans accidentally ingest the infective eggs of the dog or cat ascarid. Thelarvae migrate through the deep tissues, including the eye; and the appropriate test ofchoice is the serology. 5. The following organisms are linked with specific, relevant information. The

incorrect combination is: a. Strongyloides stercoralis - internal autoinfection b. Echinococcus granulosus - hydatid disease c. Taenia solium – human can serve as definitive and intermediate hosts d. Schistosoma mansoni - common within the United States ANSWER (d): Schistosoma mansoni is a blood fluke that is pathogenic for humans;these particular worms reside in the veins over the large intestine. The egg has a verylarge lateral spine; eggs can be recovered from the stool in infected patients. Theinfection is not endemic within the United States. However, the eggs may be seen inproficiency testing specimens. So, although it is not common, laboratories must stillbe able to identify these organisms.

6. Examination of a 24 hour unpreserved urine specimen is sometimes helpful in

the recovery of: a. Trichomonas vaginalis trophozoites b. Schistosoma haematobium eggs c. Enterobius vermicularis eggs d. Strongyloides stercoralis larvae ANSWER (b): Schistosoma haematobium blood flukes reside in the veins over thebladder. When the eggs are passed from the body, they are often found in urine; eggviability can also be determined. 7. The examination of sputum and stool may be necessary to diagnose infection

with: a. Paragonimus westermani b. Trichinella spiralis c. Wuchereria bancrofti d. Fasciola hepatica ANSWER (a): Paragonimus westermani adult worms are found in the lung and eggsmay be coughed up in the sputum. Consequently, both sputum and/or stool (if thesputum containing the eggs is swallowed) are the recommended specimens forexamination for the eggs. 8. Two helminth eggs that may resemble one another are: a. Diphyllobothrium latum and Paragonimus westermani b. Opisthorchis sinensis and Fasciolopsis busk i c. Taenia saginata and Hymenolepis nana d. Ascaris lumbricoides and Trichostrongylus ANSWER (a): Both Diphyllobothrium latum and Paragonimus westermani eggs areoperculated and approximately the same size. The morphology is similar, in spite ofthe fact that D. latum has a knob at the abopercular end and P. westermani has athickened abopercular end and shoulders into which the operculum fits. 9. Eating poorly cooked pork can lead to an infection with: a. Taenia solium and Trichinella spiralis b. Taenia saginata and Hymenolepis nana c. Trichuris trichiura and Hymenolepis diminuta d. Diphyllobothrium latum and Ascaris lumbricoides ANSWER (a): Both Taenia solium (pork tapeworm) and Trichinella spiralis can beacquired from the ingestion of raw or poorly cooked infective pork. 10. An operculated cestode egg that can be recovered in human feces is: a. Clonorchis sinensis b. Diphyllobothrium latum c. Paragonimus westermani d. Dipylidium caninum ANSWER (b): Diphyllobothrium latum is the only operculated cestode egg that is foundin humans; the infection is acquired from the ingestion of raw fresh water fish. 11. The adult tapeworm of Echinococcus granulosus is found in the intestine of: a. Humans b. Sheep c. Dogs d. Cattle ANSWER (c): While the hydatid cysts are found in sheep or in humans (accidentalintermediate host), the adult tapeworms of Echinococcus granulosus are found in theintestine of the dog. 12. In infections with Taenia solium, man can serve as the: a. definitive host b. intermediate host c. definitive and/or the intermediate host d. none of the above

ANSWER (c): If humans ingest Taenia solium cysticerci in uncooked or rare pork, theadult tapeworm will mature within the intestine (human will serve as definitive host); ifeggs from the adult tapeworm are ingested, then the cysticerci will develop in humantissues (accidental intermediate host), causing cysticercosis. 13. Humans acquire infections with Diphyllobothrium latum adult worms by: a. ingestion of fresh water crabs b. skin penetration of cercariae c. ingestion of water chestnuts d. ingestion of infected raw fresh water fish ANSWER (d): The ingestion of raw fresh water fish containing the encysted larvae ofDiphyllobothrium latum will result in the development of an adult tapeworm within thehuman intestine. 14. Humans can serve as both the intermediate and definitive host in infections

caused by: a. Enterobius vermicularis b Hymenolepis nana c. Schistosoma japonicum d. Ascaris lumbricoides ANSWER (b): Hymenolepis nana is one of the tapeworms where humans serve as bothintermediate and definitive hosts. When ingested, the oncosphere penetrates theintestinal mucosa, develops into the mature cysticercoid (human is intermediate host),and returns to the gut where the adult tapeworm matures (human is definitive host). 15. Organisms (and infections) that under normal conditions could not be

transmitted in the laboratory are: a. Hymenolepis nana – dwarf tapeworm disease b. Taenia solium - cysticercosis c. Ascaris lumbricoides - ascariasis d. Enterobius vermicularis - pinworm infection ANSWER (c): Ascaris lumbricoides eggs require a period of development in the soilbefore they are infective for humans. The other organisms listed could be transmittedwithin the laboratory or in the hospital setting. 16. Which microfilariae are usually not found circulating in the peripheral blood? a. Brugia malayi b. Loa loa c. Wuchereria bancrofti d. Onchocerca volvulus ANSWER (d): The microfilariae of Onchocerca volvulus are normally found in the fluidright under the outer layer of skin. Therefore, the skin snip is the proper specimen toexamine. 17. The miracidial hatching test helps to demonstrate the viability of: a. eggs of Taenia species. b. eggs of Schistosoma species. c. eggs of hookworm species. d. eggs of Opisthorchis. ANSWER (b): The determination of egg viability is important in schistosomiasis;therefore, the miracidial hatching test would be helpful in demonstrating the eggviability of Schistosoma species. Once the eggs were hatched, the living miracidiumlarvae would be visible in the water. 18. The incorrect match between organism and characteristic is: a. Fasciola hepatica and liver infection b. Trichuris trichiura and eggs with polar plugs c. Echinococcus granulosus and daughter cysts d. Schistosoma mansoni and egg with terminal spine ANSWER (d): The egg of Schistosoma mansoni is characterized by having a largelateral spine; S. haematobium has the characteristic terminal spine. 19. An immunosuppressed male had several episodes of pneumonia, intestinal

pain, and sepsis with Gram negative rods, and a history of military service inSoutheast Asia 20 years earlier. The organism is:

a. Fasciolopsis busk i b. Strongyloides stercoralis c. Hookworm d. Paragonimus westermani ANSWER (b): A latent infection with Strongyloides stercoralis acquired years beforemay cause severe symptoms in the immunosuppressed patient (“autoinfective”capability of life cycle and migratory route through the body). 20. Eosinophilic meningoencephalitis is a form of larva migrans causing fever,

headache, stiff neck, and increased cells in the spinal fluid. It is generally amild and self-limited infection and is caused by:

a. Necator americanus b. Angiostrongylus cantonensis c. Ancylostoma braziliense d. Strongyloides stercoralis ANSWER (b): Eosinophilic meningoencephalitis is a form of larva migrans and iscaused by Angiostrongylus cantonensis, the rat lungworm. This Pacific area infectionis associated with CSF symptoms and sometimes eye involvement. 21. When humans have cystic hydatid disease, the causative agent and host

classification are: a. Echinococcus granulosus - accidental intermediate host. b. Echinococcus granulosus - definitive host. c. Taenia solium - accidental intermediate host. d. Taenia solium - definitive host. ANSWER (a): The cause of cystic hydatid disease is Echinococcus granulosus and thehuman is classified as the accidental intermediate host. Infection occurs whenhumans ingest E. granulosus eggs and the hydatid cyst(s) develop in the liver and lungof the human instead of sheep (normal cycle). 22. A 45 year old hunter developed fever, myalgia, and periorbital edema. He has

a history of bear meat consumption. The most likely causative agent is: a. Toxoplasma gondii b. Taenia solium c. Hymenolepis nana d. Trichinella spiralis ANSWER (d): Infected bear meat is an excellent source of Trichinella spiralis. In thiscase, the patient had evidently consumed poorly cooked bear meat, thus ingesting theencysted larvae of T. spiralis. 23. This condition results from the accidental ingestion of helminth eggs. In this

instance the human becomes the intermediate rather than the definitive host. The correct answer is:

a. trichinosis b. cysticercosis. c. ascariasis. d. strongyloidiasis. ANSWER (b): The accidental ingestion of Taenia solium eggs can result in the diseasewe call cysticercosis. The cysticerci will develop in a number of different tissues,including the brain, and the human is the accidental intermediate host. 24. After returning from a 2 year stay in India, the patient had eosinophilia, an

enlarged left spermatic cord and bilateral inguinal lymphadenopathy. Themost likely clinical specimen and organism match would be:

a. thin blood films and Leishmania spp. b. urine and concentration for Trichomonas vaginalis. c. thin blood films and Babesia. d. thick blood films and microfilariae. ANSWER (d): Based on the history, the most relevant procedure to perform would bethe preparation and examination of thick blood films for the recovery andidentification of microfilariae. The symptoms suggest early filariasis.

25. Which of the following is true about onchocerciasis? a. The adult worm is present in the blood. b. The microfilariae are in the blood during the late evening hours. c. The diagnostic test of choice is the skin snip. d. The parasite resides in the deep lymphatics. ANSWER (c): The adult Onchocerca volvulus reside in subcutaneous nodules and themicrofilariae are found in the fluids right under the outer layers of skin; thus theappropriate diagnostic test is the microscopic examination of skin snips for thepresence of microfilariae. 26. Worldwide, the most prevalent helminth to infect humans is: a. Enterobius vermicularis, the pinworm. b. Ascaris lumbricoides, the large intestinal roundworm. c. Taenia saginata, the beef tapeworm. d. Schistosoma mansoni, one of the blood flukes ANSWER (a): The pinworm, Enterobius vermicularis, may be the most commonparasitic infection throughout the world and the eggs are infective within just a fewhours. Some have said that “You either had the infection as a child, have it now, orwill have it again when you have children.” 27. A helminth egg is described as having terminal polar plugs. The most likelyhelminth would be: a. Hookworm b. Trichuris trichiura c. Fasciola hepatica d. Dipylidium caninum ANSWER (b): The eggs of Trichuris trichiura (the whipworm) have been described asbeing barrel-shaped with a thick shell and two polar plugs. 28. Ingestion of which of the following will result in human infection: a. Egg of Strongyloides stercoralis b. Egg of Schistosoma japonicum c. Egg of Toxocara canis d. Egg of Opisthorchis sinensis ANSWER (c): The eggs of Toxocara canis are infectious for humans and cause viscerallarva migrans. These ascarid eggs of the dog can infect humans; the eggs hatch andthe larvae wander though the deep tissues, occasionally the eye. In this case, thehuman becomes the accidental intermediate host. 29. A helminth egg is described as having a thick radially striated shell and the

shell contains a six-hooked embryo called the oncosphere. This egg is: a. Hookworm b. Schistosoma spp. c. Strongyloides stercoralis d. Taenia spp. ANSWER (d): Taenia spp. cestode eggs have a thick radially striated shell that containsa six-hooked embryo called the oncosphere. Although the oncosphere can usually beseen in eggs found in fresh or recently preserved stool, occasionally the embryo maybe more difficult to see in eggs that have been stored for long periods in formalin. The radial striations can be seen more closely in the middle and right eggs.

31. The following proglottid was seen in a fresh stool specimen; the proglottid was

subsequently injected with India ink. Which of the following is the correct

identification?

a. Taenia saginata b. Hymenolepis diminuta c. Dipylidium caninum d. Taenia solium ANSWER (a): Based on the number of uterine branches (counted on one side only), T.saginata generally has around 16-18 lateral branches (more than 12), while T. soliumtends to have about 8-10 (less than 12). It is important to remember to count thebranches right where they come off the central stem and to count one side only. 32. A freshwater snail is always a part of the life cycle in which of the followinggroups? a. Cestodes b. Trematodes c. Filarial worms d. Intestinal nematodes ANSWER (b): In all groups of trematodes, there is a freshwater snail in the life cycle. These worms are represented by liver and lung flukes, intestinal flukes, and the bloodflukes, all of which are trematodes. 33. In the left hand column fill in the blank preceding the name of the organism ortopic with one letter from the right hand column. Use each letter only once. 1. _____ Hymenolepis nana a. proglottids wider than long2. _____ Schistosoma mansoni egg b. 3/8" long3. _____ Enterobius vermicularis adult c.giant intestinal fluke4. _____ Taenia solium egg d.large lateral spine5. _____ Trichuris trichiura egg e internal infection, hyperinfection syndrome6. _____ Taenia solium proglottid f. sheathed microfilariae7. _____ Hymenolepis diminuta egg g. egg similar to Trichuris, but with striated shell8. _____ Wuchereria bancrofti h.responsible for blood-loss anemia 9. _____ Echinococcus granulosus i. egg with polar filaments 10._____ Fasciola hepatica j. daughter cysts11. _____ Paragonimus spp. k.recovery of helminth eggs and larvae12. _____ Ascaris lumbricoides egg l. egg with bumpy shell13. _____ Sedimentation concentration m. scolex with four suckers and no hooks14. _____ Hookworm spp. n less than 12 lateral uterine branches 15. _____ Permanent stained smear o. egg with no polar filaments16. _____ Fasciolopsis busk i p.confirm protozoa (trophozoites, cysts)17. _____ Capillaria spp. q.oval shaped with polar plugs 18. _____ Strongyloides stercoralis r.examine both stool and sputum for eggs19. _____ Diphyllobothrium latum s.radially striated shell containing oncosphere20. _____ Taenia saginata adult t.liver fluke ANSWER: The appropriate responses are listed below:1. i 6. n 11. r 16. c2. d 7. o 12. l 17. g3. b 8. f 13. k 18. e4. s 9. j 14. h 19. a5. q 10. t 15. p 20. m 34. Because mature infectious eggs are ingested from the soil, which of the

following parasites might be seen in the same patient at the same time? a. Hookworm and Ascaris lumbricoides b. Ascaris lumbricoides and Trichuris trichiura c. Trichuris trichiura and Schistosoma japonicum d. Schistosoma japonicum and Hookworm ANSWER (b): The eggs of both Ascaris lumbricoides and Trichuris trichiura mustmature for a period of time in the soil before they are infectious. Infection occurswhen the human ingests these infectious eggs from the soil. Since both nematodes

are endemic in the same areas of the world, they are often seen as a mixed infectionin humans who have accidentally ingested the mature eggs from contaminated soil. 35. Which of the following helminth eggs would not float using the zinc sulfate

flotation concentration method? a. Paragonimus spp. and Diphyllobothrium latum b. Opisthorchis sinensis and Taenia spp. c. Fasciola hepatica and Hymenolepis nana d. Unfertilized Ascaris lumbricoides and Trichuris trichiura ANSWER (a): Using the zinc sulfate flotation concentration method, heavy eggs(unfertilized A. lumbricoides eggs) and operculated eggs (Paragonimus, D. latum, O.sinensis, F. hepatica) will not float using this method. The egg opercula pop open dueto the high specific gravity of the zinc sulfate, fill with zinc sulfate, and sink to thebottom of the tube. Therefore, using this method, both the surface film and sedimentmust be examined before reporting the concentration as negative.

REFERENCES

Garcia, L.S. 2007. Diagnostic Medical Parasitology, 5th Ed., ASM

Press, Washington, D.C.

© Copyright 2005 Medical Chemical Corporation (MCC). All rights reserved.Web site developed by Xcite Marketing Services and maintained by Alex Wang