General Parasitology MCQs

Option D - Microsporidia are unicellular obligate intracellular parasites. They reproduce in host cells by producing spores. 3 genera and 13 species are associated with human disease particularly, in HIV and other immuno-compromised patients. Infection is caused by an inhalation or ingestion of spores. Though commonly causes diarrhea, it may also lead to extra intestinal infections like sinusitis, cholangitis, bronchiolitis and kerato- conjunctivitis. Because of its intracellular locations, they are not routinely demonstrated by hematoxylin and eosin stain. Modified trichrome stain, gram stain and modified acid-fast stain are usually used to demonstrate them. Reference: Paniker's textbook of Parasitology - 8th Edition, Pg. No. -106

Paratenic host : An organism that harbors the sexually immature parasite (larva) but is not necessary for the parasite's developmental cycle to progress. Reservoir host : an organism that harbors a pathogen but suffers no ill effects, responsible for continued existence of parasite in area Accidental host : an organism that generally does not allow transmission to the definitive host, thereby preventing the parasite from completing its development. Definite host : An organism in which the parasite reaches the adult stage and reproduces sexually Reference: Paniker's textbook of Parasitology - 8th Edition, Pg. No. -1

Option A – L.donovani is present intracellularly in monocytes or macrophages in PBS as L-D body. Option B – T.brucei and T.cruzi are present extracellularly in plasma. Option D – Babesia are present in RBCs. Schistosomes though present in vesical and pelvic plexuses, it is never demonstrable in peripheral blood smear due to its location in capillaries of internal organs. Reference : Paniker’s textbook of Parasitology - 8th Edition, Pg. No. -7

Option C - As the thick smear concentrates 20-30 layers of RBC in a small area, it is more sensitive and requires more blood. Fixation is not required. As the RBCS are destroyed due to the dehemoglobinaztion, the characteristics like RBC enlargement and stippling cannot be seen. So, species identification is difficult. Reference : Paniker's textbook of Parasitology - 8th Edition, Pg. No. -82

Option C - There are many ways by which humans acquired Toxoplasma infection. Consumption of oocyst in cats faces through contaminated food or water is a common mode of infection. Ingesting contaminated pork or lamb containing tissue cyst can also lead to infection. As the parasite resides inside reticuloendothelial cells, humans can also acquire infection through blood transfusion & organ transplant. The parasite is also able to cross the placenta, producing congenital infection. Reference: Paniker's textbook of Parasitology - 8th Edition, Pg. No. -93

Option C - Hydatid cyst in humans is due to ingestion of contaminated eggs excreted in dog feces, along with food and water. Thus, humans are intermediate hosts, while dogs are definitive hosts. E.granulosus is one of the smallest tapeworms. Reference: Paniker's textbook of Parasitology - 8th Edition, Pg. No. 129-130

Option D - Cercariae are infective forms to humans, which enter through skin penetration. Once inside the blood vessels, they lose their tails and convert into schistosomules. When they reach mesenteric venous plexuses, they convert into adult forms. Living in copula, females produce eggs, which passes along with feces or urine, and reach water. Eggs containing ciliated embryo (miracidium) hatch immediately and release miracidium. Miracidium enters snails and successively pass through stages of first and second generation sporocyst. Sporocyst convert into cercariae which escape from snails in water. Stage of redia is not found in Schistosomes. Reference: Paniker's textbook of Parasitology - 8th Edition, Pg. No. 143

Option C – Trichinella spiralis is acquired due to consumption of pork. T.spiralis has a direct life cycle requiring only a single host to complete the life cycle. Pigs are the optimum host. Humans are accidentally infected due to consumption of pork, representing the dead end of life cycle. Option A – Consumption of pork which contains cysticercus cellulosae (larva of T.solium) can lead to taeniasis initially but not cysticercosis. However, later on due to autoinfection, the patient might get cysticercosis. Option D – Clonorchiasis is due to consumption of contaminated fish. Option B- Toxoplasmosis occurs due to consumption of oocyst which are excreted in cat feces. Reference : Paniker’s textbook of Parasitology - 8th Edition, Pg. No. -171