Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 61: The Casoni Test is positive in which of the following conditions?

A. Diphtheria
B. Scarlet fever
C. Echinococcus infection (Correct Answer)
D. Kala Azar

Explanation: **Explanation:** The **Casoni Test** is an immediate hypersensitivity (Type I) skin test historically used for the diagnosis of **Hydatid disease**, caused by the larval stage of the cestode ***Echinococcus granulosus*** [1]. **Why Echinococcus is correct:** The test involves the intradermal injection of 0.2 ml of sterile hydatid fluid (filtered from human or sheep cysts). A positive reaction is indicated by the formation of a large wheal (≥ 1.5 cm) with surrounding erythema within 20 minutes. While highly sensitive, it has been largely replaced by modern serological assays (ELISA, Western Blot) and imaging (USG/CT) due to its low specificity and the risk of anaphylaxis. **Analysis of Incorrect Options:** * **A. Diphtheria:** The relevant skin test is the **Schick Test**, which determines immunity status by detecting the presence of circulating antitoxin. * **B. Scarlet Fever:** The **Dick Test** is used to identify susceptibility to the erythrogenic toxin produced by *Streptococcus pyogenes*, while the **Schultz-Charlton reaction** is used for diagnosis (blanching of the rash). * **C. Kala Azar:** The **Montenegro Test** (leishmanin skin test) is used to detect delayed-type hypersensitivity (Type IV) to *Leishmania* antigens. **High-Yield Clinical Pearls for NEET-PG:** * **Hydatid Cyst:** Characterized by "Water Lily sign" or "Camelot sign" on imaging due to detached endocyst membranes [1]. * **Treatment of Choice:** Surgical removal (PAIR technique) combined with **Albendazole** [1]. * **Casoni Test Specificity:** It can show cross-reactivity with *Taenia solium* (Cysticercosis) and *Fasciola hepatica*.

Question 62: The Maltese cross formation is characteristic of which of the following infections?

A. Schistosomiasis
B. Babesiosis (Correct Answer)
C. Cryptococcosis
D. Sporotrichosis

Explanation: **Explanation:** The **Maltese cross formation** is a pathognomonic finding in **Babesiosis**, an infection caused by the protozoan *Babesia microti*. Inside the host's erythrocytes, the parasite undergoes asexual reproduction (budding), resulting in four daughter cells (merozoites) that remain attached by their bases. This tetrad arrangement resembles a "Maltese cross" and is a high-yield diagnostic feature on a Giemsa-stained peripheral blood smear. **Analysis of Options:** * **Babesiosis (Correct):** Characterized by intra-erythrocytic tetrads. It is often confused with *Plasmodium falciparum*, but Babesia lacks malarial pigment (hemozoin) and intracellular gametocytes. * **Schistosomiasis:** Known for characteristic eggs with spines (e.g., terminal spine in *S. haematobium* and lateral spine in *S. mansoni*), not tetrad formations. * **Cryptococcosis:** *Cryptococcus neoformans* is a budding yeast with a thick polysaccharide capsule. While it shows "Maltese cross" appearance under **polarized light** in urinalysis (due to lipiduria), the classic morphological description in tissue is a "narrow-based bud." * **Sporotrichosis:** Caused by *Sporothrix schenckii*, it typically presents as "cigar-shaped" yeast cells in tissue. **NEET-PG High-Yield Pearls:** 1. **Vector:** *Ixodes* tick (same vector as Lyme disease and Anaplasmosis). 2. **Clinical Presentation:** Fever, hemolytic anemia, and hemoglobinuria; severe in asplenic patients. 3. **Drug of Choice:** Atovaquone + Azithromycin (or Clindamycin + Quinine for severe cases). 4. **Distinction:** Unlike Malaria, *Babesia* can show extracellular rings.

Question 63: What is the recommended chemoprophylaxis for pregnant females traveling to areas endemic for chloroquine-resistant Plasmodium falciparum?

A. Primaquine
B. Doxycycline
C. Amodiaquine
D. Mefloquine (Correct Answer)

Explanation: **Explanation:** The management of malaria in pregnancy is a high-yield topic for NEET-PG, as it requires balancing maternal-fetal safety with drug efficacy. **Why Mefloquine is correct:** In areas with chloroquine-resistant *P. falciparum*, **Mefloquine** is the drug of choice for chemoprophylaxis in pregnant women. It is considered safe in all three trimesters of pregnancy. The standard regimen is 250 mg once weekly, starting 1–2 weeks before travel and continuing for 4 weeks after returning. **Analysis of Incorrect Options:** * **Primaquine (A):** It is strictly **contraindicated** in pregnancy because it can cross the placenta and cause life-threatening hemolysis in a G6PD-deficient fetus. It is also contraindicated in individuals with known G6PD deficiency. * **Doxycycline (B):** It is **contraindicated** in pregnancy (Category D) as it can cause permanent dental discoloration and affect bone growth in the fetus (Tetracycline effect). * **Amodiaquine (C):** While used in some treatment combinations (ACTs), it is not a standard recommendation for travel prophylaxis due to the risk of hepatitis and agranulocytosis with prolonged use. **High-Yield Clinical Pearls for NEET-PG:** 1. **Chloroquine-Sensitive Areas:** Chloroquine remains the drug of choice for prophylaxis in pregnancy if the region is sensitive. 2. **Mefloquine Contraindications:** Avoid in patients with a history of **psychiatric disorders** (depression, psychosis) or **seizures**, as it can lower the seizure threshold and exacerbate neuropsychiatric symptoms. 3. **Alternative:** If Mefloquine is contraindicated, **Atovaquone-Proguanil** is generally avoided in pregnancy due to limited data, though it may be considered if no other options exist. 4. **Treatment vs. Prophylaxis:** For the *treatment* of uncomplicated falciparum malaria in the 1st trimester, Quinine + Clindamycin is the traditional choice, though ACTs (like Artemether-Lumefantrine) are now increasingly recommended by the WHO for all trimesters.

Question 64: Which of the following is true about Giardia?

A. May cause traveler's diarrhea (Correct Answer)
B. Giardia inhabits mainly the ileum
C. Trophozoites are infective to humans
D. None of the above

Explanation: **Explanation:** **1. Why Option A is Correct:** *Giardia lamblia* (also known as *G. intestinalis* or *G. duodenalis*) is a common cause of **Traveler’s Diarrhea**, particularly in individuals consuming contaminated water in endemic areas. The diarrhea is typically non-bloody, foul-smelling, and associated with steatorrhea (fatty stools) due to malabsorption caused by the parasite coating the intestinal mucosa. **2. Why Other Options are Incorrect:** * **Option B:** Giardia primarily inhabits the **duodenum and upper jejunum**, not the ileum. It prefers the acidic environment of the upper small intestine. * **Option C:** The **Cyst** is the infective stage for humans. Trophozoites are the vegetative, feeding stage found in the intestine; if passed in feces, they cannot survive the external environment or gastric acidity, making them non-infective upon ingestion. **3. NEET-PG High-Yield Clinical Pearls:** * **Morphology:** The trophozoite is "pear-shaped" or "heart-shaped" with a **"Falling Leaf" motility** and a characteristic "Monkey Face" appearance (due to two nuclei and four pairs of flagella). * **Pathogenesis:** It causes malabsorption by blunting villi and inhibiting enzymes like disaccharidases. It does **not** invade the bloodstream (no extraintestinal manifestations). * **Diagnosis:** Stool microscopy (cysts/trophozoites) or the **String Test (Entero-test)** to sample duodenal fluid. * **Immunology:** Patients with **IgA deficiency** are highly susceptible to chronic giardiasis. * **Treatment:** Drug of choice is **Metronidazole** or Tinidazole.

Question 65: LD bodies are associated with which of the following?

A. Larva migrans
B. Kala azar (Correct Answer)
C. Malaria
D. Loa loa

Explanation: **Explanation:** **Leishman-Donovan (LD) bodies** are the diagnostic hallmark of **Kala-azar** (Visceral Leishmaniasis), caused by the protozoan *Leishmania donovani*. In the human host, the parasite exists in the **amastigote form**, which are small, oval, non-flagellated bodies (2–4 µm) found multiplying within the reticuloendothelial cells, particularly macrophages of the spleen, liver, and bone marrow. These amastigotes are what we clinically refer to as LD bodies. **Analysis of Options:** * **Kala-azar (Correct):** LD bodies are identified in splenic or bone marrow aspirates stained with Giemsa or Leishman stain. They are characterized by a nucleus and a distinct rod-shaped kinetoplast. * **Larva migrans:** This is caused by the migration of nematode larvae (e.g., *Ancylostoma braziliense* for cutaneous or *Toxocara canis* for visceral). Diagnosis depends on clinical presentation or identifying larvae, not LD bodies. * **Malaria:** Caused by *Plasmodium* species. Diagnostic stages include ring forms, trophozoites, schizonts, and gametocytes within or outside RBCs. * **Loa loa:** A filarial nematode (African eye worm). Diagnosis involves identifying microfilariae in peripheral blood films, typically collected during the day (diurnal periodicity). **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Sandfly (*Phlebotomus argentipes*). * **Infective Stage:** Promastigote (flagellated form found in the sandfly). * **Diagnostic Stage:** Amastigote (LD bodies in humans). * **Culture Medium:** NNN (Novy-MacNeal-Nicolle) medium. * **Gold Standard Diagnosis:** Splenic aspirate (highest sensitivity) or Bone marrow aspirate (safer). * **Classic Triad:** Fever, massive splenomegaly, and pancytopenia. Hypergammaglobulinemia is also a characteristic finding.

Question 66: Which of the following is NOT true about Entamoeba Histolytica?

A. Mature cysts are typically 4-nucleated. (Correct Answer)
B. Mature cysts are typically 8-nucleated.
C. Trophozoites colonize the colon.
D. All of the above statements are true.

Explanation: **Explanation:** The correct answer is **Option B (Mature cysts are typically 8-nucleated)** because this statement is **false** regarding *Entamoeba histolytica*. 1. **Why Option B is the "Not True" statement:** The life cycle of *E. histolytica* involves the ingestion of mature cysts. A hallmark diagnostic feature of *E. histolytica* is that its **mature cyst contains exactly 4 nuclei** (quadrinucleate). In contrast, the non-pathogenic commensal *Entamoeba coli* is characterized by mature cysts that typically contain **8 nuclei**. Distinguishing the number of nuclei is a high-yield point for microscopic differentiation. 2. **Analysis of other options:** * **Option A:** This is a **true** statement. The infective stage is the quadrinucleate cyst. * **Option C:** This is a **true** statement. The trophozoites primarily colonize the large intestine (colon and cecum), where they can cause "flask-shaped" ulcers by invading the mucosa. * **Option D:** This is incorrect because Option B is a false statement. **NEET-PG High-Yield Pearls:** * **Infective Stage:** Mature quadrinucleate cyst. * **Diagnostic Stage:** Trophozoites (in acute dysentery) or cysts (in chronic/carrier states) in stool. * **Pathognomonic Feature:** Trophozoites containing **ingested RBCs** (Erythrophagocytosis) indicate active invasive disease. * **Morphology:** Cysts also contain **chromatoid bars** with rounded/blunt ends (cigar-shaped), whereas *E. coli* has bars with splintered/frayed ends. * **Complication:** The most common extra-intestinal site is the liver (**Amoebic Liver Abscess**), typically presenting with "anchovy sauce" pus.

Question 67: Which of the following is true about Giardia?

A. Complement fixation test is diagnostic
B. Trophozoites and cysts are seen in man (Correct Answer)
C. It lives in the lower intestine
D. It invades the normal mucosa

Explanation: **Explanation:** *Giardia lamblia* (also known as *G. duodenalis* or *G. intestinalis*) is a flagellated protozoan that exists in two stages: the **trophozoite** (vegetative form) and the **cyst** (infective form). **Why Option B is Correct:** In the human host, both stages are present. Trophozoites reside in the small intestine, where they multiply by binary fission. As they pass through the colon, they undergo encystation. Consequently, both trophozoites (typically in diarrheal stools) and cysts (in formed stools) can be detected in human fecal samples. **Analysis of Incorrect Options:** * **Option A:** Diagnosis is primarily made via **stool microscopy** (demonstrating cysts/trophozoites) or stool antigen detection (ELISA). Complement fixation tests are not used for routine diagnosis as they lack specificity and sensitivity for *Giardia*. * **Option C:** *Giardia* primarily inhabits the **upper small intestine** (duodenum and upper jejunum). It does not live in the lower intestine (colon). * **Option D:** *Giardia* is **non-invasive**. It attaches to the intestinal epithelium using a ventral sucking disc, causing malabsorption (steatorrhea) by "carpeting" the mucosa, but it does not invade the tissue or enter the bloodstream. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Trophozoites are pear-shaped with a **"falling leaf" motility** and a characteristic **"monkey face"** appearance (two nuclei and four pairs of flagella). * **Clinical Feature:** Causes **Steatorrhea** (foul-smelling, greasy stools) due to fat malabsorption. * **Association:** Increased incidence in patients with **IgA deficiency**. * **Drug of Choice:** Tinidazole or Metronidazole.

Question 68: Chiggerosis is caused by which of the following?

A. Bed bug
B. Louse
C. Tick
D. Mite (Correct Answer)

Explanation: **Explanation:** **Chiggerosis** (also known as Trombidiasis) is an infestation caused by the **larval stage** of **Trombiculid mites**, commonly referred to as "chiggers" or "harvest mites." 1. **Why Mite is Correct:** Unlike adult mites, only the six-legged larvae are parasitic. They attach to the skin (often at tight clothing lines) and inject digestive enzymes to liquefy skin cells (forming a feeding tube called a **stylostome**). This results in intense pruritus, dermatitis, and erythematous papules. 2. **Why other options are incorrect:** * **Bed bugs (*Cimex lectularius*):** Cause "Cimicosis," characterized by linear tracks of bites ("breakfast, lunch, and dinner" pattern), but do not cause chiggerosis. * **Louse (*Pediculus/Phthirus*):** Causes Pediculosis (head, body, or pubic lice). * **Tick:** Ticks are vectors for diseases like Rickettsial fever and Lyme disease, but their infestation is not termed chiggerosis. (Note: Do not confuse "Chiggerosis" with "Tungiasis," which is caused by the Tunga penetrans flea). **High-Yield Clinical Pearls for NEET-PG:** * **Vector Potential:** Trombiculid mites (*Leptotrombidium deliense*) are the primary vectors for **Scrub Typhus** (caused by *Orientia tsutsugamushi*). * **The Eschar:** The site of a chigger bite in Scrub Typhus often develops into a pathognomonic "cigarette burn" appearance called an **eschar**. * **Habitat:** Chiggers are typically found in low-lying damp vegetation or "scrub" islands. * **Treatment:** Symptomatic relief with antihistamines/topical steroids; Scrub Typhus is treated with Doxycycline.

Question 69: Malabsorption is caused by all of the following parasitic infections EXCEPT:

A. Giardia
B. Ascaris lumbricoides (Correct Answer)
C. Strongyloides
D. Capillaria philippinensis

Explanation: **Explanation:** The correct answer is **Ascaris lumbricoides**. While *Ascaris* is a major cause of protein-energy malnutrition and vitamin A deficiency due to nutrient competition, it does **not** typically cause a clinical malabsorption syndrome. Its primary pathology involves intestinal obstruction (bolus formation) or migration into the biliary tract. **Why the other options are incorrect (Causes of Malabsorption):** * **Giardia lamblia:** The most common protozoan cause of malabsorption. It causes "blunting of villi" and coats the intestinal mucosa, leading to physical interference with nutrient absorption and steatorrhea. * **Strongyloides stercoralis:** This helminth penetrates the duodenal and jejunal mucosa. In heavy infections, it causes significant mucosal inflammation and flattening of villi, leading to a malabsorption syndrome. * **Capillaria philippinensis:** This parasite causes "sprue-like" symptoms. It leads to severe enteropathy with protein-losing enteropathy and electrolyte imbalance (notably hypokalemia) due to mucosal damage. **NEET-PG High-Yield Pearls:** 1. **Giardiasis:** Look for "foul-smelling, floating stools" and "falling leaf motility" on microscopy. It is the classic cause of fat malabsorption. 2. **Capillaria philippinensis:** Often associated with the consumption of raw freshwater fish; causes "Borrheic" (borborygmi) and severe wasting. 3. **Coccidian Parasites:** *Cryptosporidium*, *Cyclospora*, and *Cystoisospora* are also major causes of malabsorption, especially in immunocompromised (HIV) patients. 4. **Ascaris:** The most common complication is **intestinal obstruction** at the ileocecal valve. Diagnosis is by finding bile-stained eggs in stool.

Question 70: Parasitic Encephalitis is caused by which of the following organisms?

A. Naegleria (Correct Answer)
B. Acanthamoeba
C. Balamuthia
D. Gnathostoma

Explanation: **Explanation:** The correct answer is **Naegleria fowleri**. While all the listed organisms can involve the Central Nervous System (CNS), the term "Parasitic Encephalitis" in a classic MCQ context specifically refers to **Primary Amoebic Meningoencephalitis (PAM)** caused by *Naegleria fowleri*. **1. Why Naegleria is correct:** *Naegleria fowleri* is a free-living amoeba found in warm freshwater. It enters the body through the nasal mucosa (usually during swimming/diving), penetrates the cribriform plate, and migrates to the brain. It causes an acute, fulminant, and usually fatal **Primary Amoebic Meningoencephalitis (PAM)**. It is characterized by rapid brain tissue destruction and hemorrhagic necrosis. **2. Why the other options are incorrect:** * **Acanthamoeba & Balamuthia mandrillaris:** These cause **Granulomatous Amoebic Encephalitis (GAE)**. Unlike the acute PAM caused by *Naegleria*, GAE is a chronic, subacute infection typically seen in immunocompromised individuals. * **Gnathostoma spinigerum:** This is a nematode that causes **Neurognathostomiasis**. While it involves the CNS, it typically presents as eosinophilic meningitis or radiculitis due to larval migration, rather than the classic "amoebic encephalitis" clinical picture. **High-Yield Clinical Pearls for NEET-PG:** * **Naegleria fowleri:** Known as the "Brain-eating amoeba." * **Diagnostic Clue:** Look for a history of swimming in stagnant water followed by rapid onset of meningeal signs. * **CSF Finding:** Purulent CSF (high neutrophils) but **no bacteria** on Gram stain; trophozoites may be seen on a wet mount (showing "slug-like" pseudopodia). * **Drug of Choice:** Amphotericin B (often used in combination with Miltefosine). * **Culture:** Grown on **Non-nutrient agar** seeded with *E. coli*.

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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