MLT GlobeParasitology: Lab diagnosis & methods
37 Parasitology MCQs on Lab diagnosis & methods with answers and explanations.
In a protozoan life cycle, what is the active, motile stage that feeds and multiplies inside the host called?
The trophozoite is the vegetative, feeding and dividing form. Sporozoites and merozoites are invasive stages of apicomplexans, and gametocytes are sexual precursor cells.
A parasite that cannot complete its life cycle or survive without a host is termed:
Obligate parasites depend entirely on a host. Facultative parasites can also live freely, accidental parasites infect an unusual host, and 'paratenic' describes a transport host, not a parasite type.
When scanning a stool smear for helminth eggs, which objective gives the largest field of view?
The field of view shrinks as magnification rises, so the 10× objective covers the most area and is used for scanning. Higher objectives are used to confirm detail.
An animal that harbours a human parasite and keeps it circulating in nature when no human host is available is called a:
Reservoir hosts (e.g. dogs for Leishmania infantum, pigs for Balantidium) maintain the parasite and act as a source of human infection. Intermediate and definitive hosts are defined by the stage they carry.
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.
Medical parasitology covers protozoa, helminths and arthropods. Which group falls OUTSIDE its scope?
Coccobacilli are bacteria, studied in bacteriology. Protozoa, helminths and medically important arthropods are the three pillars of parasitology.
A patient with tissue-invasive helminth infection has marked eosinophilia. Which antibody class is characteristically raised?
Helminths stimulate a Th2 response with IL-4/IL-5, raising total and specific IgE and eosinophils. IgA and IgM are not the characteristic markers.
The host in which a parasite reaches sexual maturity and reproduces sexually is the:
Adult or sexual stages live in the definitive host; larval or asexual stages develop in intermediate hosts, and paratenic hosts carry larvae without development.
Which of the following does NOT live in the blood or blood cells?
D. latum is an intestinal tapeworm. Plasmodium and Babesia infect red cells, and trypanosomes circulate in plasma.
Which statement correctly describes protozoa?
Protozoa are single-celled eukaryotes with a true nucleus; helminths are multicellular and bacteria prokaryotic.
A direct wet mount of stool is negative, but intestinal parasites are still suspected. What should be done next?
Formalin-ethyl acetate sedimentation or flotation concentrates cysts and eggs, increasing sensitivity. India ink is used for Cryptococcus in CSF.
Metazoan parasites, such as helminths and arthropods, are:
Metazoa are multicellular animals with differentiated tissues. Protozoa are unicellular.
A parasite living within the body of its host, such as a tapeworm, is called:
Endoparasites live inside the host, while ectoparasites such as lice and ticks live on the surface.
Protozoa formerly grouped in the class Mastigophora move by means of:
Mastigophora are the flagellates, such as Giardia, Trichomonas and trypanosomes. Cilia are found in ciliates and pseudopodia in amoebae.
In the name Plasmodium falciparum, the word 'Plasmodium' is the:
Binomial names give the genus first, capitalized, then the species epithet (falciparum). Plasmodium belongs to the phylum Apicomplexa.
The most common form of asexual reproduction in protozoa is:
Most protozoa, such as amoebae and flagellates, divide into two daughter cells. Schizogony occurs in Apicomplexa, and conjugation is a sexual process in ciliates.
On a thin film, 250 of 10,000 red cells counted contain malaria parasites. What is the parasitemia?
Parasitemia = infected RBCs ÷ total RBCs × 100 = 250 ÷ 10,000 × 100 = 2.5%. Count infected cells, not individual parasites, on thin films.
Why is a thick blood film used together with a thin film for malaria diagnosis?
Thick films lyse red cells and examine more blood, so they are more sensitive. Thin films are methanol-fixed, keeping red cells intact for morphology and species identification.
Giemsa stain for malaria films gives the best stippling (Schüffner dots) when the buffer pH is:
Giemsa buffered to pH 7.0–7.2 shows parasite chromatin, cytoplasm and stippling best. Acidic pH makes stippling poor and red cells too pink.
For routine ova and parasite (O&P) examination, the recommended collection is:
Parasites are shed irregularly, so up to three specimens on different days improve detection. Barium and some medications interfere and should be avoided for 5–10 days.