MLT GlobeDOH exam preparation (Abu Dhabi) – page 9
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Entamoeba coli lives in the human colon feeding on bacteria and debris, gaining food while causing the host no harm or benefit. This relationship is called:
In commensalism one partner benefits while the other is unaffected. In mutualism both benefit, and in parasitism the host is harmed.
How do most medically important fungi reproduce and disperse?
Fungi multiply mainly through spores (conidia, sporangiospores, ascospores and others), which are also what laboratories identify microscopically. Cysts, ova and trophozoites belong to protozoa or helminths.
A skin scraping is treated with KOH plus calcofluor white to look for fungal hyphae. Which microscope is needed to read it?
Calcofluor white binds chitin and cellulose and fluoresces blue-white under UV/blue excitation, so a fluorescence microscope is required. It is not visible with ordinary bright-field illumination.
Humans acquire Taenia saginata by eating undercooked meat from its intermediate host. Which animal is that?
Cysticercus bovis develops in cattle muscle; humans are the definitive host. Pigs are the intermediate host of T. solium, fish of Diphyllobothrium, and dogs are definitive hosts of Echinococcus.
Which protozoan infection is classified as a sexually transmitted infection?
T. vaginalis is spread mainly by sexual intercourse and is the commonest non-viral STI. The others are faeco-oral infections, though amoebiasis and giardiasis can occasionally follow oral-anal sex.
Schistosomes live in the mesenteric or vesical venous plexuses. Which common name reflects this?
Adult schistosomes live in blood vessels, hence 'blood flukes'. Fasciola/Clonorchis are liver flukes, Paragonimus a lung fluke and Fasciolopsis an intestinal fluke.
'Ringworm' (tinea) of the skin is caused by which organism?
Ringworm is a dermatophyte fungal infection caused by Microsporum, Trichophyton or Epidermophyton; no worm is involved. Cryptococcus is a yeast causing meningitis.
Taenia solium has a flat, segmented body with a scolex bearing suckers and hooks. To which helminth class does it belong?
Segmented, ribbon-like worms with a scolex are cestodes (tapeworms). Nematodes are unsegmented and cylindrical; trematodes are leaf-shaped and unsegmented.
The entry of a parasite into a host followed by its establishment and multiplication is termed:
Infection is the invasion and multiplication of an organism in a host, whether or not symptoms follow. Disease requires damage, while virulence and pathogenicity describe the organism's capacity to cause harm.
Lactophenol cotton blue (LPCB) mounting fluid is routinely used in the laboratory to examine:
LPCB kills, preserves and stains fungal elements (chitin takes up cotton blue), making it the standard mount for mould identification. Protozoa use iodine or trichrome; blood parasites use Giemsa.
Which genus is NOT a dermatophyte?
Dermatophytes comprise Microsporum, Trichophyton and Epidermophyton (plus newer genera like Nannizzia). Madurella causes eumycetoma, a subcutaneous infection.
Which Leishmania form, injected by the sandfly, initiates human infection?
Flagellated metacyclic promastigotes are inoculated by the sandfly and become amastigotes inside macrophages. Trypo- and epimastigotes are trypanosome stages.
A yeast from a vaginal swab is incubated in serum at 37°C for 2–3 hours and produces germ tubes. The organism is most likely:
The germ tube test presumptively identifies C. albicans (and C. dubliniensis). C. glabrata and Cryptococcus are germ tube negative; C. difficile is a bacterium.
Unstained cells are nearly transparent under a bright-field microscope. What is usually done to increase the contrast of their structures?
Stains bind cellular components selectively and create contrast. Brighter light actually reduces contrast, and a cover slip or higher eyepiece does not add it.
Chagas disease is spread when faeces of which blood-sucking insect contaminate the bite wound?
Triatomine bugs deposit T. cruzi trypomastigotes in faeces near the bite. Tsetse flies transmit African trypanosomiasis; sandflies, Leishmania.
A night-time blood sample from a patient with lymphoedema is examined for Wuchereria bancrofti. Which stage is sought?
Adult W. bancrofti live in lymphatics and release sheathed microfilariae that circulate with nocturnal periodicity. Filariae produce no eggs, trophozoites or oocysts in blood.
In an infected man, Trichomonas vaginalis is most likely to be found in which site?
T. vaginalis is a urogenital flagellate; in males it colonizes the urethra and prostate. It does not live in the gut, unlike intestinal flagellates such as Giardia.
Which of these infections is acquired without any arthropod vector?
Giardia cysts are swallowed in contaminated water or food (fecal-oral route). Malaria, leishmaniasis and yellow fever all need an insect vector.
Which of the following parasites typically causes bloody diarrhea with mucus (dysentery)?
E. histolytica invades the colonic mucosa, producing flask-shaped ulcers and dysentery with blood and mucus. P. falciparum is a blood parasite, D. latum causes vitamin B12 deficiency and Onchocerca affects skin and eyes.
Which infection does not typically cause splenomegaly?
Ascaris lives in the intestinal lumen and does not enlarge the spleen. Kala-azar and malaria cause marked splenomegaly, and S. mansoni causes it through portal hypertension.