Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 341: What is the treatment of choice for 'biian' malaria?

A. Sulfamethoxazole-pyrimethamine
B. Quinine
C. Mefloquine
D. Chloroquine (Correct Answer)

Explanation: **Explanation:** The term **"Benign Tertian Malaria"** refers to infections caused by *Plasmodium vivax* or *Plasmodium ovale*. These species are characterized by a 48-hour erythrocytic cycle, leading to paroxysms every third day. **1. Why Chloroquine is the Correct Answer:** Chloroquine remains the **drug of choice** for sensitive strains of *P. vivax* and *P. ovale*. It is a rapidly acting blood schizonticide that eliminates the asexual erythrocytic stages, thereby terminating the clinical attack. However, to achieve a "radical cure" and prevent relapse from dormant liver stages (hypnozoites), Chloroquine must be followed by a 14-day course of **Primaquine** (after screening for G6PD deficiency). **2. Why Other Options are Incorrect:** * **Sulfamethoxazole-pyrimethamine (Option A):** Primarily used for uncomplicated *P. falciparum* in specific combinations, but high resistance rates have limited its use. It is not the first-line treatment for vivax malaria. * **Quinine (Option B):** Reserved for severe or complicated malaria and chloroquine-resistant cases. It has a narrower therapeutic index and more side effects (Cinchonism). * **Mefloquine (Option C):** Used for prophylaxis in travelers or as an alternative for multi-drug resistant *P. falciparum*. It is not preferred for benign tertian malaria due to neuropsychiatric side effects. **Clinical Pearls for NEET-PG:** * **Malignant Tertian Malaria:** Caused by *P. falciparum*. * **Quartan Malaria:** Caused by *P. malariae* (72-hour cycle). * **Drug of Choice for Pregnancy:** Chloroquine is safe in all trimesters for sensitive malaria. * **Relapse vs. Recrudescence:** *P. vivax/ovale* cause **relapse** (due to hypnozoites); *P. falciparum/malariae* cause **recrudescence** (due to persistent blood stages).

Question 342: Which of the following is a causative agent of Visceral Leishmaniasis?

A. Leishmania braziliensis
B. Leishmania panamensis
C. Leishmania donovani (Correct Answer)
D. Leishmania major

Explanation: **Explanation:** **Leishmania donovani** is the primary causative agent of **Visceral Leishmaniasis (VL)**, also known as **Kala-azar**. In the Indian subcontinent, it is the sole species responsible for the disease. The parasite targets the reticuloendothelial system (liver, spleen, and bone marrow), leading to the classic triad of prolonged fever, massive splenomegaly, and pancytopenia. **Analysis of Options:** * **Leishmania donovani (Correct):** It causes the visceral form of the disease. In India, it is transmitted by the sandfly *Phlebotomus argentipes*. * **Leishmania braziliensis & L. panamensis (Incorrect):** These species belong to the *Viannia* subgenus and are primarily responsible for **Mucocutaneous Leishmaniasis (Espundia)** and Cutaneous Leishmaniasis in Central and South America. * **Leishmania major (Incorrect):** This species is a common cause of **Old World Cutaneous Leishmaniasis** (Oriental Sore), typically presenting as self-healing skin ulcers. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Female Sandfly (*Phlebotomus* species). * **Infective Stage:** Promastigote (flagellated form found in the sandfly). * **Diagnostic Stage:** Amastigote (LD bodies) found within macrophages in bone marrow or splenic aspirates. * **Gold Standard Diagnosis:** Splenic aspiration (highest sensitivity, but risky); Bone marrow aspiration is the most common clinical practice. * **RK-39 Immunochromatographic test:** Best rapid screening test for field use. * **Drug of Choice:** Liposomal Amphotericin B is currently the preferred treatment. * **Post-Kala-azar Dermal Leishmaniasis (PKDL):** A non-ulcerative skin condition that develops in some patients after the apparent cure of VL, acting as a reservoir for the parasite.

Question 343: All of the following statements about the Sabin-Feldman Dye test are true, except:

A. It is a serological test for Toxoplasma.
B. It uses Methylene blue dye.
C. It may remain positive for years.
D. Bluish staining of trophozoites indicates a positive test. (Correct Answer)

Explanation: The **Sabin-Feldman Dye Test** is the gold standard serological reference test for diagnosing **Toxoplasmosis**. Understanding its mechanism is crucial for NEET-PG. ### Why Option D is the Correct Answer (The "Except" Statement) The test is based on the principle that specific antibodies against *Toxoplasma gondii*, in the presence of a complement-like "accessory factor," will neutralize the parasite. * **Negative Test:** In the absence of antibodies, the cell membrane of the live trophozoites remains intact, allowing **Methylene blue** to enter and stain the cytoplasm **blue**. * **Positive Test:** When specific antibodies are present, they damage the parasite's membrane. Consequently, the trophozoites lose their affinity for the dye and remain **unstained/colorless**. Therefore, **bluish staining indicates a negative result**, making Option D the false statement. ### Analysis of Other Options * **Option A:** It is indeed the classic serological test for *Toxoplasma gondii*, measuring IgG antibodies. * **Option B:** Alkaline Methylene blue is the specific dye used to visualize the trophozoites. * **Option C:** IgG antibodies against Toxoplasma typically appear 1–2 weeks after infection and can persist at detectable levels for many years, or even life. ### High-Yield Clinical Pearls * **Gold Standard:** While rarely performed now due to the need for live tachyzoites (biohazard risk), it remains the reference standard. * **Accessory Factor:** The test requires a heat-labile serum component (complement-like) obtained from Toxoplasma-negative individuals. * **Alternative Tests:** In modern practice, ELISA (for IgM/IgG) and PCR are more commonly used. * **Congenital Toxoplasmosis Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications.

Question 344: Which of the following is TRUE about Acute Primary Amoebic Meningoencephalitis?

A. Meningitis caused by Acanthamoeba species is acute in nature
B. Diagnosis is by demonstration of trophozoite in CSF (Correct Answer)
C. Caused by fecal-oral transmission
D. More common in tropical climates

Explanation: **Explanation:** **Primary Amoebic Meningoencephalitis (PAM)** is a rapidly fatal central nervous system infection caused by the free-living amoeba, ***Naegleria fowleri***. **Why Option B is Correct:** The definitive diagnosis of PAM is made by the **microscopic demonstration of motile trophozoites** in a fresh sample of **Cerebrospinal Fluid (CSF)**. Unlike other amoebae, *Naegleria fowleri* exists in the brain and CSF only as trophozoites (never as cysts). On a wet mount, these trophozoites exhibit characteristic "slug-like" pseudopodial movement. **Analysis of Incorrect Options:** * **Option A:** *Acanthamoeba* species cause **Granulomatous Amoebic Encephalitis (GAE)**, which is a **chronic**, subacute infection typically seen in immunocompromised individuals. PAM (caused by *Naegleria*) is the one that is acute and fulminant. * **Option C:** Transmission is **not fecal-oral**. Infection occurs when contaminated water is forcefully inhaled or splashed into the nose (e.g., during diving or swimming), allowing the amoeba to penetrate the **cribriform plate** and migrate along the olfactory nerves to the brain. * **Option D:** While it can occur in the tropics, it is specifically associated with **warm freshwater** (lakes, hot springs, or poorly chlorinated pools) during hot summer months in temperate regions as well. The key risk factor is the temperature of the water, not just the climate zone. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Amphotericin B (often used in combination with Miltefosine). * **CSF Findings:** Resembles pyogenic meningitis (high neutrophils, low sugar, high protein), but the presence of RBCs (hemorrhagic) and the absence of bacteria on Gram stain should raise suspicion for PAM. * **Morphology:** *Naegleria fowleri* is the only free-living amoeba with a flagellated stage (biflagellate) in its life cycle.

Question 345: Nematodes are differentiated from other worms by which characteristic?

A. Absence of segmentation (Correct Answer)
B. Presence of a separate celomic cavity
C. Separation of sexes
D. Cylindrical body shape

Explanation: **Explanation:** Nematodes (roundworms) are characterized by a **non-segmented, cylindrical body** covered by a tough, resistant cuticle. In the context of differentiating them from other helminths (Platyhelminthes), the **absence of segmentation** is a primary diagnostic feature. **Why the correct answer is right:** * **Absence of Segmentation:** Unlike Cestodes (tapeworms), which are divided into proglottids (segments), Nematodes possess a continuous, unsegmented body wall. This is a fundamental morphological distinction used in taxonomic classification. **Analysis of Incorrect Options:** * **Presence of a separate celomic cavity:** Nematodes do not have a true coelom; they possess a **pseudocoelom** (a body cavity not entirely lined by mesoderm). This distinguishes them from Annelids (true coelomates). * **Separation of sexes:** While most nematodes are dioecious (separate sexes), this is not an exclusive differentiator. Some Trematodes (e.g., *Schistosoma*) also exhibit separate sexes, whereas most other flatworms are hermaphroditic. * **Cylindrical body shape:** While "roundworm" implies a cylindrical shape, some nematodes (like the female *Enterobius* or *Trichuris*) may have tapered or whip-like ends, and some larval stages of other phyla can appear cylindrical. Lack of segmentation is a more definitive taxonomic marker. **NEET-PG Clinical Pearls:** * **Body Wall:** Nematodes have a **cuticle, hypodermis, and a single layer of longitudinal muscles** (no circular muscles), leading to their characteristic thrashing movement. * **Digestive System:** Unlike Trematodes and Cestodes, Nematodes have a **complete digestive tract** with both a mouth and an anus. * **High-Yield Example:** *Ascaris lumbricoides* is the largest nematode infecting the human intestine; its lack of segments and presence of a pseudocoelom are classic exam points.

Question 346: Which of the following is associated with respiratory symptoms?

A. Rocky mountain spotted fever
B. Strongyloides (Correct Answer)
C. T. Solium
D. Onchocerca

Explanation: **Explanation:** The correct answer is **Strongyloides stercoralis**. This parasite is associated with respiratory symptoms due to its complex life cycle involving **pulmonary migration** (Loeffler’s syndrome). 1. **Why Strongyloides is correct:** After larvae penetrate the skin, they enter the bloodstream and travel to the lungs. They break into the alveolar spaces, causing symptoms like cough, wheezing, and dyspnea. They are then coughed up and swallowed to reach the intestine. In immunocompromised patients (especially those on steroids), *Strongyloides* can cause **Hyperinfection Syndrome**, leading to severe hemorrhagic pneumonia and ARDS. 2. **Why other options are incorrect:** * **Rocky Mountain Spotted Fever:** Caused by *Rickettsia rickettsii*, it typically presents with a triad of fever, headache, and a characteristic petechial rash starting on wrists and ankles. While severe cases can involve the lungs, it is primarily a vasculitic disease. * **T. solium (Pork Tapeworm):** Primarily causes intestinal infection or **Neurocysticercosis** (seizures/brain cysts). It does not have a pulmonary migration phase. * **Onchocerca volvulus:** Causes "River Blindness" and dermatitis. The microfilariae migrate through the subcutaneous tissue and eyes, not the respiratory tract. **NEET-PG High-Yield Pearls:** * **Loeffler’s Syndrome:** Remember the mnemonic **NASSA** for helminths that migrate through lungs: ***N**ecator americanus, **A**scaris lumbricoides, **S**trongyloides stercoralis, **S**chistosomes, **A**ncylostoma duodenale*. * *Strongyloides* is unique because it can cause **autoinfection**, allowing the infection to persist for decades. * **Drug of choice:** Ivermectin (Albendazole is an alternative).

Question 347: What indicates the pathogenicity of Entamoeba histolytica?

A. Isoenzyme pattern (Correct Answer)
B. Size
C. Nuclear pattern
D. ELISA test

Explanation: **Explanation:** The pathogenicity of *Entamoeba histolytica* is primarily determined by its **isoenzyme pattern (Zymodeme analysis)**. 1. **Why Isoenzyme pattern is correct:** *Entamoeba histolytica* (pathogenic) and *Entamoeba dispar* (non-pathogenic) are morphologically identical. They are differentiated by their zymodemes—groups of amoebae that share the same electrophoretic mobility for specific enzymes (like hexokinase and malate dehydrogenase). Pathogenic strains typically show specific bands that are absent in non-pathogenic commensals. 2. **Why other options are incorrect:** * **Size:** Both *E. histolytica* and *E. dispar* fall within the same size range (10–60 µm for trophozoites). Size helps differentiate *E. histolytica* from *E. hartmanni* (the "small race"), but not for determining pathogenicity. * **Nuclear pattern:** Both pathogenic and non-pathogenic species share the characteristic "cartwheel" nucleus (central karyosome and fine peripheral chromatin). * **ELISA test:** While ELISA can detect antigens or antibodies, it is a diagnostic tool for infection rather than a biological indicator of the strain's inherent pathogenicity. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for Differentiation:** While zymodeme analysis was the traditional method, **PCR** is now the gold standard for distinguishing *E. histolytica* from *E. dispar*. * **Erythrophagocytosis:** The presence of ingested RBCs in a trophozoite is the only morphological feature that strongly suggests pathogenicity (*E. histolytica*). * **Cyst Stage:** The mature cyst is quadrinucleate (4 nuclei) with rounded chromatoid bars. * **Anchovy Sauce Pus:** Characteristic of an Amoebic Liver Abscess (the most common extra-intestinal manifestation).

Question 348: Which one of the following tests is used for the diagnosis of Giardia lamblia infection?

A. Enterotest (Correct Answer)
B. Casoni's test
C. Parasite F test
D. Napier's test

Explanation: **Explanation:** **Giardia lamblia** is a flagellated protozoan that primarily inhabits the duodenum and upper jejunum. While stool microscopy for cysts and trophozoites is the standard initial investigation, the **Enterotest (String Test)** is a specialized diagnostic tool used when stool examinations are repeatedly negative but clinical suspicion remains high. 1. **Why Enterotest is Correct:** In this procedure, the patient swallows a gelatin capsule containing a weighted nylon string. The capsule dissolves in the stomach, and the string moves into the duodenum. After 4–6 hours, the string is withdrawn. The bile-stained mucus adhering to the string is scraped and examined microscopically for motile trophozoites. This is highly effective because *Giardia* colonizes the exact area the string samples. 2. **Why Other Options are Incorrect:** * **Casoni’s Test:** An immediate hypersensitivity skin test used for diagnosing **Hydatid disease** (*Echinococcus granulosus*). It has largely been replaced by serology (ELISA). * **Parasite F Test:** This is not a standard diagnostic term in parasitology. It may be a distractor or a confusion with the "Fecal Occult Blood Test." * **Napier’s Test (Aldehyde Test):** Used for the presumptive diagnosis of **Visceral Leishmaniasis (Kala-azar)**. It depends on the increase in serum gamma globulins. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *Giardia* trophozoites have a characteristic "falling leaf" motility and a "monkey face" appearance (two nuclei and four pairs of flagella). * **Pathogenesis:** It causes malabsorption (steatorrhea) by "carpeting" the duodenal mucosa, leading to the blunting of villi. It does **not** invade the bloodstream. * **Drug of Choice:** Metronidazole or Tinidazole. * **Stool Findings:** Look for "foul-smelling, bulky, greasy stools" in the clinical stem.

Question 349: What is the chief source of most parasitic diseases in humans?

A. Mosquitoes
B. Birds
C. Fish
D. Humans (Correct Answer)

Explanation: **Explanation:** In medical parasitology, the **source of infection** refers to the individual or object from which the infectious agent passes to the host. For the majority of human parasitic diseases, **Humans** serve as the primary reservoir and chief source of infection. This occurs through various cycles, most notably the **man-to-man** transmission (e.g., *Entamoeba histolytica*, *Enterobius vermicularis*, and *Giardia lamblia*). Even in vector-borne diseases like Malaria, humans act as the essential reservoir from which mosquitoes acquire the parasite to infect others. **Analysis of Options:** * **Humans (Correct):** Most parasites are highly host-specific. Humans act as the definitive host for many species, shedding eggs, cysts, or larvae in feces or urine, which then contaminate the environment and infect other humans. * **Mosquitoes:** While mosquitoes are the most significant **vectors** (transmitting Malaria, Filariasis), they are the *vehicle* of transmission rather than the primary source or reservoir for the majority of all parasitic infections globally. * **Birds:** Birds serve as reservoirs for specific zoonotic infections (e.g., certain *Schistosoma* species causing swimmer's itch), but they contribute to a negligible fraction of total human parasitic disease. * **Fish:** Fish act as intermediate hosts for specific helminths (e.g., *Diphyllobothrium latum*, *Clonorchis sinensis*), but these are geographically localized and not the "chief" source worldwide. **NEET-PG High-Yield Pearls:** * **Autoinfection:** Seen in *Strongyloides stercoralis*, *Hymenolepis nana*, and *Enterobius vermicularis*. * **Soil-Transmitted Helminths (STH):** The "Unholy Trinity" includes *Ascaris*, Trichuris, and Hookworm; humans are the sole source. * **Reservoir Host:** An animal that harbors the parasite and serves as a source of infection to humans (e.g., dogs for *Leishmania donovani* in certain regions).

Question 350: Chronic amoebic keratitis is seen in which of the following organisms?

A. E. histolytica
B. Acanthamoeba (Correct Answer)
C. Naegleria
D. Haemoflagellates

Explanation: **Explanation:** **Acanthamoeba** is the correct answer because it is a free-living amoeba known to cause two distinct clinical conditions: **Acanthamoeba Keratitis** and Granulomatous Amoebic Encephalitis (GAE). Acanthamoeba keratitis is a chronic, sight-threatening infection of the cornea typically associated with **contact lens wearers** (due to contaminated cleaning solutions) or trauma involving brackish water/soil. The hallmark clinical feature is a characteristic **ring-shaped corneal infiltrate** and intense pain out of proportion to clinical findings. **Analysis of Incorrect Options:** * **E. histolytica:** This is an obligate parasite primarily causing intestinal amoebiasis (dysentery) and extra-intestinal abscesses (most commonly in the liver). It does not cause keratitis. * **Naegleria fowleri:** Known as the "brain-eating amoeba," it causes **Primary Amoebic Meningoencephalitis (PAM)**, a rapidly fatal acute infection. It enters via the olfactory mucosa during swimming but does not affect the cornea. * **Haemoflagellates:** This group includes *Leishmania* and *Trypanosoma*, which cause systemic diseases like Kala-azar and Sleeping Sickness, respectively, rather than localized corneal infections. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Acanthamoeba is identified by seeing **star-shaped cysts** or trophozoites on corneal scrapings. * **Culture:** It is grown on **Non-nutrient agar (NNA) overlaid with E. coli**. * **Staining:** Calcofluor white or Periodic acid-Schiff (PAS) stains are used to highlight the cysts. * **Risk Factor:** Using tap water to rinse contact lenses is a classic board-exam scenario for this condition.

Practice by Chapter

Classification of Parasites

Practice Questions

Intestinal Protozoa

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Blood and Tissue Protozoa

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Malaria Parasites

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Leishmaniasis

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Intestinal Helminths: Nematodes

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Tissue Nematodes

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Trematodes

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Cestodes

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Ectoparasites

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Antiparasitic Drugs

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Laboratory Diagnosis of Parasitic Infections

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