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Parasitology Exam (Helminths)

 

***Reminder:  Slides and examination questions are copyrighted and cannot be copied for 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 aspirated from a cyst.  Immature scolices and/or hooklets would be found in the centrifuged fluid sediment 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-Leyden crystals.  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 by the short buccal capsule (mouth) and large genital primordium; these hookworm larvae 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 occurs when humans accidentally ingest the infective eggs of the dog or cat ascarid.  The larvae migrate through the deep tissues, including the eye; and the appropriate test of choice 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 very large lateral spine; eggs can be recovered from the stool in infected patients.  The infection is not endemic within the United States.  However, the eggs may be seen in proficiency testing specimens.  So, although it is not common, laboratories must still be 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 the bladder.  When the eggs are passed from the body, they are often found in urine; egg viability 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 eggs may be coughed up in the sputum.  Consequently, both sputum and/or stool (if the sputum containing the eggs is swallowed) are the recommended specimens for examination for the eggs.

 

8.         Two helminth eggs that may resemble one another are:

 

                        a.         Diphyllobothrium latum and Paragonimus westermani

                        b.         Opisthorchis sinensis and Fasciolopsis buski

                        c.         Taenia saginata and Hymenolepis nana

                        d.         Ascaris lumbricoides and Trichostrongylus

 

ANSWER (a):  Both Diphyllobothrium latum and Paragonimus westermani eggs are operculated and approximately the same size.  The morphology is similar, in spite of the fact that D. latum has a knob at the abopercular end and P. westermani has a thickened 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 be acquired 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 found in 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 (accidental intermediate host), the adult tapeworms of Echinococcus granulosus are found in the intestine 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, the adult tapeworm will mature within the intestine (human will serve as definitive host); if eggs from the adult tapeworm are ingested, then the cysticerci will develop in human tissues (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 of Diphyllobothrium latum will result in the development of an adult tapeworm within the human 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 both intermediate and definitive hosts.  When ingested, the oncosphere penetrates the intestinal 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 soil before they are infective for humans.  The other organisms listed could be transmitted within 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 fluid right under the outer layer of skin.  Therefore, the skin snip is the proper specimen to examine.

 

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 egg viability of Schistosoma species.  Once the eggs were hatched, the living miracidium larvae 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 large lateral 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 in Southeast Asia 20 years earlier.  The organism is:   

                        a.         Fasciolopsis buski        

                        b.         Strongyloides stercoralis                       

                        c.         Hookworm

                        d.         Paragonimus westermani

 

ANSWER (b):  A latent infection with Strongyloides stercoralis acquired years before may 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 a mild 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 is caused by Angiostrongylus cantonensis, the rat lungworm.  This Pacific area infection is 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 the human is classified as the accidental intermediate host.  Infection occurs when humans ingest E. granulosus eggs and the hydatid cyst(s) develop in the liver and lung of 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 this case, the patient had evidently consumed poorly cooked bear meat, thus ingesting the encysted 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 disease we 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.  The most 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 be the preparation and examination of thick blood films for the recovery and identification 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 the microfilariae are found in the fluids right under the outer layers of skin; thus the appropriate diagnostic test is the microscopic examination of skin snips for the presence 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 common parasitic infection throughout the world and the eggs are infective within just a few hours.  Some have said that “You either had the infection as a child, have it now, or will have it again when you have children.”

 

27.        A helminth egg is described as having terminal polar plugs.  The most likely helminth 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 as being 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 visceral larva migrans.  These ascarid eggs of the dog can infect humans; the eggs hatch and the larvae wander though the deep tissues, occasionally the eye.  In this case, the human 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 contains a six-hooked embryo called the oncosphere.  Although the oncosphere can usually be seen in eggs found in fresh or recently preserved stool, occasionally the embryo may be 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. solium tends to have about 8-10 (less than 12).  It is important to remember to count the branches 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 following groups?

 

                        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 blood flukes, all of which are trematodes.

 

33.        In the left hand column fill in the blank preceding the name of the organism or topic with one letter from the right hand column.  Use each letter only once.

 

1.  _____           Hymenolepis nana                    a. proglottids wider than long

2.  _____           Schistosoma mansoni egg        b. 3/8" long

3.  _____           Enterobius vermicularis adult     c.giant intestinal fluke

4.  _____           Taenia solium egg                    d.large lateral spine

5.  _____           Trichuris trichiura egg               e internal infection, hyperinfection syndrome

6.  _____           Taenia solium proglottid            f. sheathed microfilariae

7.  _____           Hymenolepis diminuta egg    g. egg similar to Trichuris, but with striated shell

8.  _____           Wuchereria bancrofti                h.responsible for blood-loss anemia                    

9.  _____           Echinococcus granulosus         i. egg with polar filaments                           

10._____           Fasciola hepatica                     j. daughter cysts

11. _____          Paragonimus spp.                    k.recovery of helminth eggs and larvae

12. _____          Ascaris lumbricoides egg          l. egg with bumpy shell

13. _____          Sedimentation concentration     m. scolex with four suckers and no hooks

14. _____          Hookworm spp.                        n less than 12 lateral uterine branches      

15. _____          Permanent stained smear         o. egg with no polar filaments

16. _____          Fasciolopsis buski                   p.confirm protozoa (trophozoites, cysts)

17. _____          Capillaria spp.                          q.oval shaped with polar plugs    

18. _____          Strongyloides stercoralis            r.examine both stool and sputum for eggs

19. _____          Diphyllobothrium latum              s.radially striated shell containing oncosphere

20. _____          Taenia saginata adult                 t.liver fluke

 

 

ANSWER:  The appropriate responses are listed below:

1.  i                               6.  n                              11.  r               16.  c

2.  d                             7.  o                             12.  l                  17.  g

3.  b                             8.  f                              13.  k                 18.  e

4.  s                              9.  j                               14.  h               19.  a

5.  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 must mature for a period of time in the soil before they are infectious.  Infection occurs when 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 infection in 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 due to the high specific gravity of the zinc sulfate, fill with zinc sulfate, and sink to the bottom of the tube.  Therefore, using this method, both the surface film and sediment must be examined before reporting the concentration as negative. 

 

REFERENCES

Garcia, L.S. 2016. Diagnostic Medical Parasitology, 6th Ed., ASM Press, Washington, D.C.