PARASITOLOGY (HARR 5TH EDITION)

• The incorrect match between organism and the appropriate diagnostic procedure is:

  A. Onchocerca volvulus—examination of skin snips

  B. Cryptosporidium spp.—modified acid-fast stain

  C. Enterobius vermicularis—routine ova and parasite examination

  D. Schistosoma haematobium—examination of urine sediment

  C
• In a patient with diarrhea, occasionally Entamoeba histolytica/E. dispar (four nucleated cysts, no chromatoidal bars) are identified as being present; however, these cells, which are misdiagnosed as protozoa, are really:

  A. Macrophages

  B. Polymorphonuclear leukocytes (PMNs)

  C. Epithelial cells

  D. Eosinophils

  B
• Charcot-Leyden crystals in stool may be associated with an immune response and are thought to be formed from the breakdown products of:

  A. Neutrophils

  B. Eosinophils

  C. Monocytes

  D. Lymphocytes

  B
• Parasitic organisms that may be transmitted sexually do not include:

  A. Entamoeba gingivalis

  B. Dientamoeba fragilis

  C. Trichomonas vaginalis

  D. Diphyllobothrium latum

  D
• The appropriate procedure for the diagnosis of E. vermicularis would involve the microscopic examination of a series of consecutive cellulose tapes. Typical eggs and/or a rare adult pinworm could be identified under the microscope.
• As Polymorphonuclear leukocytes (PMNs) in stool begin to fragment and appear to have four nuclei, they will resemble E. histolytica/E. dispar cysts. However, E. histolytica/E. dispar cysts are rarely seen in cases of diarrhea. The species name E. histolytica is reserved for the true pathogen, whereas E. dispar is used for the nonpathogenic species. Unfortunately, they look identical morphologically. The only time E. histolytica could be identified morphologically would be from trophozoites containing ingested RBCs.
• Nonpathogenic E. dispar would not contain ingested RBCs. The correct way to report these organisms is E. histolytica/E. dispar (no trophozoites containing ingested RBCs) or E. histolytica (trophozoites seen that contain ingested RBCs). Physicians may base the treatment on patient symptoms.
• When eosinophils disintegrate, the granules reform into Charcot-Leyden crystals.
• Diphyllobothrium latum cannot be transmitted sexually; this infection is acquired from the ingestion of infected raw or poorly cooked freshwater fish.
• The incorrect match between the organism and one method of acquiring the infection is:

  A. Trypanosoma brucei rhodesiense—bite of sand fleas

  B. Giardia lamblia (G. intestinalis, G. duodenalis)—ingestion of water contaminated with

  cysts

  C. Hookworm—skin penetration of larvae from soil

  D. Toxoplasma gondii—ingestion of infected raw or rare meats

  A
• Upon examination of stool material for Cystoisospora belli, one would expect to see:

  A. Cysts containing sporozoites

  B. Precysts containing chromatoidal bars

  C. Oocysts that are modified acid-fast positive

  D. Sporozoites that are hematoxylin positive

  C
• Which specimen is the least likely to provide recovery of Trichomonas vaginalis?

  A. Urine

  B. Urethral discharge

  C. Vaginal discharge

  D. Feces

  D
• Which of the following is the best technique to identify Dientamoeba fragilis in stool?

  A. Formalin concentrate

  B. Trichrome-stained smear

  C. Modified acid fast–stained smear

  D. Giemsa stain

  B
• One of the following protozoan organisms has been implicated in waterborne and foodborne outbreaks within the United States. The suspect organism is:

  A. Pentatrichomonas hominis

  B. Dientamoeba fragilis

  C. Giardia lamblia (G. intestinalis, G. duodenalis)

  D. Balantidium coli

  C
• Gram staining of a sample from a gum lesion showed what appeared to be amoebae. A trichrome smear showed amoebae with a single nucleus and partially digested PMNs. The correct identification is:

  A. Trichomonas tenax

  B. Entamoeba histolytica/Entamoeba dispar

  C. Entamoeba gingivalis

  D. Entamoeba polecki

  C
• East and West African trypanosomiasis (T. B. rhodesiense and T. B. gambiense) are acquired when infective forms are introduced into the human body through the bite of the tse-tse fly, not sand fleas.
• Cystoisospora belli oocysts in various stages of maturity would be seen in the concentrate sediment or possibly the direct, wet preparation; these oocysts would stain positive with modified acid-fast stains.
• T. vaginalis is site-specific. The organisms are found in the urogenital tract; thus, the intestinal tract is not the normal site for these organisms.
• The best technique to recover and identify D. fragilis trophozoites and rare cysts would be the trichrome-stained smear.
• For a number of years, G. lamblia (G. intestinalis, G. duodenalis) has been implicated in both waterborne and foodborne outbreaks from the ingestion of infective cysts within water and food.
• E. gingivalis is known to be an inhabitant of the mouth and is characterized by that resembles E. histolytica/E. dispar. However, E. gingivalis tends to ingest PMNs, whereas E. histolytica/E. dispar do not.
• An E. histolytica (true pathogen) trophozoite has the following characteristics:

  A . Compact karyosome in the nucleus, ingested RBCs, and clear pseudopodia

  B. Ingested RBCs, clear pseudopodia, and uneven chromatin on the nuclear membrane

  C. Ingested RBCs, clear pseudopodia, and large glycogen vacuoles in cytoplasm

  D. Large, blotlike karyosome, ingested white blood cells (WBCs), and granular pseudopods

  A
• A 12-year-old girl is brought to the emergency room with meningitis and a history of swimming in a warm-water spring. Motile amoebae that measure 10 μm in size are seen in CSF and are most likely:

  A. Iodamoeba bütschlii trophozoites

  B. Endolimax nana trophozoites

  C. Dientamoeba fragilis trophozoites

  D. Naegleria fowleri trophozoites

  D
• Characteristics of the rhabditiform (noninfective) larvae of Strongyloides stercoralis

  include a:

  A. Short buccal capsule and large genital primordium

  B. Long buccal capsule and pointed tail

  C. Short buccal capsule and small genital primordium

  D. Small genital primordium and notch in tail

  A
• Visceral larva migrans is associated with which of the following organisms and diagnostic method?

  A. Toxocara—serology

  B. Onchocerca—skin snips

  C. Dracunculus—skin biopsy

  D. Angiostrongylus—CSF examination

  A
• The following organisms are linked with specific, relevant information. The incorrect combination is:

  A. Strongyloides stercoralis—internal autoinfection

  B. Echinococcus granulosus—hydatid examination

  C. Toxoplasma gondii—serology

  D. Balantidium coli—common in the United States

  D
• Examination of 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

  B
• The trophozoite of E. histolytica has evenly arranged chromatin on the nuclear membrane; a central, compact karyosome in the nucleus; clear pseudopodia; and ingested RBCs in the cytoplasm.
• Naegleria fowleri are free-living soil and water amoebae that cause primary amebic meningoencephalitis (PAM). The number of cases reported is few; however, the infection is very acute and almost always fatal.
• The rhabditiform larvae of S. stercoralis are characterized by the short buccal capsule (mouth) and large genital primordium, whereas hookworm larvae have a long buccal capsule and very small genital primordium.
• Toxocara spp. are the cause of visceral larva migrans and occur when humans accidentally ingest the infective eggs of the dog or cat ascarid. The larvae migrate through the deep tissues, including the eye. The test of choice is the serology.
• Balantidium coli is a ciliate that can cause watery diarrhea in humans; however, it is not commonly found within the United States. It is the largest of the intestinal protozoa and can be found in proficiency testing specimens. Therefore, although it is not common, laboratories must still be able to identify these organisms.
• Schistozoma 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 in unpreserved urine.
• The examination of sputum may be necessary to diagnose infection with:

  A. Paragonimus westermani

  B. Trichinella spiralis

  C. Wuchereria bancrofti

  D. Fasciola hepatica

  A
• 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

  A
• Eating poorly cooked infected 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

  A
• An operculated cestode egg that can be recovered from human feces is:

  A. Clonorchis sinensis

  B. Diphyllobothrium latum

  C. Paragonimus westermani

  D. Dipylidium caninum

  B
• The adult tapeworm of Echinococcus granulosus is found in the intestine of:

  A. Dogs

  B. Sheep

  C. Humans

  D. Cattle

  A
• In infections with Taenia solium, humans can serve as the:

  A. Definitive host

  B. Intermediate host

  C. Either the definitive or the intermediate host

  D. None of the above

  C
• Humans acquire infections with Diphyllobothrium latum adult worms by:

  A. Ingestion of freshwater crabs

  B. Skin penetration of cercariae

  C. Ingestion of water chestnuts

  D. Ingestion of raw freshwater fish

  D