Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 401: Maurer's dots are seen in infection with which Plasmodium species?

A. Plasmodium malariae
B. Plasmodium vivax
C. Plasmodium ovale
D. Plasmodium falciparum (Correct Answer)

Explanation: **Explanation:** The correct answer is **Plasmodium falciparum**. **1. Why Plasmodium falciparum is correct:** Maurer’s dots are coarse, irregular, dark-staining granules (clefts) seen in the cytoplasm of red blood cells infected with *P. falciparum*. These represent protein transport organelles (Maurer’s clefts) that the parasite uses to export virulence factors, such as PfEMP1, to the erythrocyte surface. These factors lead to "knob" formation, causing cytoadherence and sequestration, which explains the high pathogenicity of falciparum malaria. **2. Why the other options are incorrect:** * **Plasmodium vivax & Plasmodium ovale:** These species characteristically show **Schüffner’s dots**. These are fine, uniform pinkish granules seen throughout the enlarged RBC. * **Plasmodium malariae:** This species shows **Ziemann’s dots**, which are fine, dusty-looking granules that appear later in the infection cycle. **3. High-Yield Clinical Pearls for NEET-PG:** To differentiate *Plasmodium* species on a peripheral smear, remember this "Dots" summary: * **Maurer’s Dots:** *P. falciparum* (Think: **F**alciparum = **F**ew, coarse dots). * **Schüffner’s Dots:** *P. vivax* and *P. ovale*. * **Ziemann’s Dots:** *P. malariae*. * **James’s Dots:** Sometimes used specifically for *P. ovale*. **Additional Morphological Clues for *P. falciparum*:** * **Accole/Applique forms:** Trophozoites at the very edge of the RBC. * **Multiple rings** per RBC. * **Banana/Crescent-shaped** gametocytes. * Absence of Schizonts in peripheral blood (due to sequestration).

Question 402: Which of the following statements regarding cysticercosis is FALSE?

A. Commonest sites are meninges and cerebral ventricles. (Correct Answer)
B. Calcification is common.
C. It causes focal neurological complications.
D. It is found in subcutaneous tissues.

Explanation: ### Explanation **Neurocysticercosis (NCC)** is the most common parasitic infection of the human central nervous system, caused by the larval stage (*Cysticercus cellulosae*) of the pork tapeworm, *Taenia solium*. **1. Why Option A is False (The Correct Answer):** While NCC involves the brain, the **commonest site for cysticerci is the brain parenchyma** (specifically the corticomedullary junction), not the meninges or ventricles. Parenchymal involvement accounts for the majority of clinical presentations, whereas intraventricular or subarachnoid (racemose) forms are less common, though often more severe due to the risk of obstructive hydrocephalus. **2. Analysis of Other Options:** * **Option B (Calcification is common):** This is a true statement. As the parasite dies, the host's immune response leads to granuloma formation and eventual **dystrophic calcification**. On a CT scan, these appear as "starry sky" hyperdense lesions. * **Option C (Focal neurological complications):** This is true. Depending on the location of the cyst, patients can present with focal deficits, hemiparesis, or most commonly, **new-onset focal seizures** (the leading cause of adult-onset epilepsy in endemic areas). * **Option D (Found in subcutaneous tissues):** This is true. Outside the CNS, the most common sites for cysticercosis are the **subcutaneous tissues and skeletal muscles**, where they appear as firm, mobile, painless nodules. **Clinical Pearls for NEET-PG:** * **Mode of Infection:** Humans acquire cysticercosis by **ingesting eggs** (via contaminated food/water or autoinfection), NOT by eating undercooked pork (which causes intestinal taeniasis). * **Diagnosis:** MRI is the gold standard for visualizing the **scolex** (appears as a "hole-with-dot" encephalopathy). * **Treatment:** Albendazole is the drug of choice; however, steroids must be administered first to prevent inflammatory edema caused by dying larvae.

Question 403: Which of the following is a vector for scrub typhus?

A. Trombiculid mite (Correct Answer)
B. Louse
C. Tick
D. Reduviid bug

Explanation: **Explanation:** **Scrub typhus** is a zoonotic rickettsial infection caused by the bacterium ***Orientia tsutsugamushi***. **1. Why Trombiculid mite is correct:** The primary vector and reservoir for scrub typhus is the **larval stage (chigger)** of the **Trombiculid mite** (*Leptotrombidium deliense*). These mites inhabit heavy scrub vegetation. The infection is transmitted to humans through the bite of an infected chigger. Notably, the bacteria are maintained in the mite population through **transovarial transmission** (from adult to egg). **2. Why other options are incorrect:** * **Louse:** The body louse (*Pediculus humanus corporis*) is the vector for **Epidemic typhus** (*Rickettsia prowazekii*). * **Tick:** Ticks are vectors for **Indian Tick Typhus** (*Rickettsia conorii*) and Rocky Mountain Spotted Fever. * **Reduviid bug:** Also known as the "kissing bug," it is the vector for **Chagas disease** (*Trypanosoma cruzi*), not rickettsial diseases. **3. High-Yield Clinical Pearls for NEET-PG:** * **The Eschar:** A painless, black, necrotic scab at the site of the chigger bite is the pathognomonic clinical sign of scrub typhus. * **Weil-Felix Test:** This heterophile antibody test shows a positive reaction with **OX-K** antigen (and is negative for OX-19 and OX-2). * **Drug of Choice:** **Doxycycline** is the gold standard treatment. * **Geography:** It is prevalent in the "Tsutsugamushi Triangle" (extending from Japan and Australia to India/Pakistan).

Question 404: In malaria, the parasite form that acts as the reservoir is?

A. Merozoite
B. Sporozoite
C. Trophozoite
D. None of the above (Correct Answer)

Explanation: ### Explanation The correct answer is **None of the above** because, in the context of malaria, the term "reservoir" refers to the host that maintains the parasite population in nature, not a specific morphological stage of the parasite. **1. Why "None of the above" is correct:** In medical parasitology, a **reservoir** is defined as an organism (or environment) in which an infectious agent normally lives and multiplies. For malaria, **humans** are the primary reservoir (the only significant vertebrate host), while the **female Anopheles mosquito** acts as the vector. The options provided (Merozoite, Sporozoite, Trophozoite) are all **developmental stages** of the parasite, not the reservoir itself. **2. Analysis of Incorrect Options:** * **Merozoite:** This stage is released from the liver (exo-erythrocytic) or red blood cells (erythrocytic). Its primary role is to infect new RBCs; it does not maintain the long-term population in the environment. * **Sporozoite:** This is the **infective stage** for humans, inoculated by the mosquito bite. It travels to the liver but does not serve as a reservoir. * **Trophozoite:** This is the metabolically active, feeding stage within the RBC. It is responsible for clinical symptoms but is not a reservoir. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Infective Stage for Humans:** Sporozoite. * **Infective Stage for Mosquito:** Gametocyte (specifically the mature forms). * **Relapse (P. vivax/P. ovale):** Caused by **Hypnozoites** (dormant stages in the liver). These are often confused with "reservoirs" within the body, but they are technically "latent stages." * **Definitive Host:** Female Anopheles mosquito (where the sexual cycle occurs). * **Intermediate Host:** Humans (where the asexual cycle occurs).

Question 405: Fish is a host for all of the following parasites except?

A. Paragonimus westermani (Correct Answer)
B. Clonorchis sinensis
C. Opisthorchis viverrini
D. Diphyllobothrium latum

Explanation: ### Explanation The correct answer is **Paragonimus westermani**. To answer this question correctly, one must distinguish between parasites that use **fish** as their second intermediate host versus those that use **crustaceans**. **1. Why Paragonimus westermani is the correct answer:** *Paragonimus westermani* (the Lung Fluke) follows a specific life cycle: the first intermediate host is a **snail**, but the second intermediate host is a **crustacean (crab or crayfish)**. Humans are infected by ingesting raw or undercooked crustacean meat containing metacercariae, not fish. **2. Analysis of Incorrect Options (Fish-borne Parasites):** * **Clonorchis sinensis (Chinese Liver Fluke):** Humans are infected by eating raw/undercooked **freshwater fish** containing metacercariae. * **Opisthorchis viverrini (Southeast Asian Liver Fluke):** Similar to *Clonorchis*, it utilizes **freshwater fish** (cyprinoid family) as the second intermediate host. * **Diphyllobothrium latum (Fish Tapeworm):** This is the longest tapeworm infecting humans. Its life cycle involves two intermediate hosts: a cyclops (crustacean) and then a **freshwater fish** (e.g., pike, perch). Humans get infected by eating raw fish containing plerocercoid larvae. **3. NEET-PG High-Yield Clinical Pearls:** * **Paragonimus westermani:** Classically presents with **hemoptysis** (mimicking Tuberculosis) and "rusty sputum." Look for a history of eating raw crabs. * **Diphyllobothrium latum:** Associated with **Vitamin B12 deficiency** and Megaloblastic anemia because the worm competes for B12 absorption in the jejunum. * **Clonorchis/Opisthorchis:** Chronic infection is a major risk factor for **Cholangiocarcinoma** (bile duct cancer). * **Heterophyes heterophyes** and **Metagonimus yokogawai** are other trematodes that also use fish as intermediate hosts.

Question 406: Which of the following statements is true about hard ticks?

A. They have four stages in their life cycle.
B. The female tick lays thousands of eggs.
C. The larval stage is known as seed ticks.
D. All of the above. (Correct Answer)

Explanation: ### Explanation Hard ticks (Family **Ixodidae**) are significant vectors of various human diseases. This question tests the fundamental biological characteristics that distinguish them from soft ticks. **1. Why the correct answer is "All of the above":** * **Life Cycle Stages (Option A):** Hard ticks undergo a complex metamorphosis consisting of four distinct stages: **Egg → Larva → Nymph → Adult**. Each stage (except the egg) requires a blood meal to progress to the next phase. * **Egg Production (Option B):** Female hard ticks are prolific breeders. Unlike soft ticks (which lay eggs in small batches), a female hard tick lays a **single massive batch of thousands of eggs** (often 3,000–8,000) and dies shortly after. * **Seed Ticks (Option C):** The larval stage is colloquially known as **"seed ticks."** These larvae are tiny, have only **six legs** (unlike the eight-legged nymphs and adults), and are often found in large clusters on vegetation waiting for a host. **2. Clinical Pearls for NEET-PG:** * **Morphology:** Hard ticks possess a dorsal chitinous shield called the **Scutum**. In males, it covers the entire back; in females, it covers only the anterior portion to allow for abdominal expansion during feeding. * **Feeding Habit:** They are "slow feeders," remaining attached to the host for several days. * **Diseases Transmitted:** * **Rickettsial:** Rocky Mountain Spotted Fever, Indian Tick Typhus. * **Bacterial:** Tularemia, Lyme disease (*Ixodes*). * **Viral:** Kyasanur Forest Disease (KFD) in India (*Haemaphysalis spinigera*). * **Tick Paralysis:** Caused by a toxin in the saliva of certain female ticks. **Summary Table for Quick Revision:** | Feature | Hard Tick (Ixodidae) | Soft Tick (Argasidae) | | :--- | :--- | :--- | | **Scutum** | Present | Absent | | **Mouthparts** | Visible from above | Hidden ventrally | | **Feeding** | Long duration (days) | Short duration (minutes) | | **Egg laying** | One large batch | Multiple small batches |

Question 407: Which of the following is/are a non-pathogenic amoeba?

A. E. histolytica
B. E. coli (Correct Answer)
C. Acanthamoeba
D. E. hamanni

Explanation: **Explanation:** The identification of non-pathogenic amoebae is crucial in clinical parasitology to avoid misdiagnosis and unnecessary treatment, as these organisms often coexist with pathogens in the human gut. **1. Why E. coli is correct:** *Entamoeba coli* is a common **commensal** (non-pathogenic) inhabitant of the large intestine. It does not invade tissues or cause disease. Its clinical significance lies in its morphological similarity to the pathogen *E. histolytica*. Key distinguishing features include its larger size, presence of more than four nuclei in the mature cyst (typically 8), and splintered/jagged chromatoid bodies. **2. Analysis of Incorrect Options:** * **A. E. histolytica:** This is the primary **pathogenic** amoeba causing amoebic dysentery and extra-intestinal manifestations like liver abscesses. It is characterized by ingested RBCs in the trophozoite stage. * **C. Acanthamoeba:** This is a **free-living pathogenic** amoeba. It causes Granulomatous Amoebic Encephalitis (GAE) in immunocompromised individuals and Amoebic Keratitis (often associated with contact lens use). * **D. E. hartmanni:** (Note: Option D likely refers to *E. hartmanni*). While *E. hartmanni* is also non-pathogenic, *E. coli* is the classic textbook example used in exams. If the option was *E. hartmanni*, it is often called "Small Race *E. histolytica*" and is non-pathogenic. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology Check:** *E. coli* cysts have **1–8 nuclei**, while *E. histolytica* cysts have a maximum of **4 nuclei**. * **Chromatoid Bodies:** *E. histolytica* has rounded/cigar-shaped ends; *E. coli* has splintered/frayed ends. * **Other Non-Pathogens:** *Entamoeba gingivalis* (found in the mouth), *Endolimax nana*, and *Iodamoeba bütschlii*. * **Pathogen Alert:** *Entamoeba moshkovskii* and *Entamoeba dispar* are morphologically identical to *E. histolytica* but are generally considered non-pathogenic; they require molecular methods (PCR) for differentiation.

Question 408: Hydatid disease is caused by which organism?

A. Echinococcus (Correct Answer)
B. Tapeworm
C. Ascaris
D. Hookworm

Explanation: **Explanation:** **Hydatid disease** (also known as Cystic Echinococcosis) is caused by the larval stage of the cestode **Echinococcus granulosus** (the dog tapeworm). Humans act as **accidental intermediate hosts** after ingesting eggs shed in the feces of definitive hosts (dogs). Once ingested, the oncosphere embryos penetrate the intestinal wall, enter the portal circulation, and primarily settle in the **liver** (most common site, ~70%) or lungs, forming slow-growing, fluid-filled cysts. **Analysis of Options:** * **A. Echinococcus (Correct):** Specifically *E. granulosus* causes cystic hydatid disease, while *E. multilocularis* causes the more aggressive alveolar hydatid disease. * **B. Tapeworm (Incorrect):** While *Echinococcus* is a type of tapeworm, this term is too broad. In medical exams, "Tapeworm" usually refers to *Taenia solium* (Pork tapeworm) or *Taenia saginata* (Beef tapeworm), which cause Taeniasis or Cysticercosis. * **C. Ascaris (Incorrect):** *Ascaris lumbricoides* is a nematode (roundworm) that causes intestinal obstruction or Loeffler’s syndrome, not hydatid cysts. * **D. Hookworm (Incorrect):** *Ancylostoma duodenale* and *Necator americanus* are nematodes that cause iron-deficiency anemia. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Ultrasound shows a "water lily sign" (detached germinal membrane) or "cartwheel/honeycomb appearance" (daughter cysts). * **Casoni Test:** An immediate hypersensitivity skin test (now largely replaced by serology/ELISA). * **Treatment:** **PAIR** (Puncture, Aspiration, Injection of scolicidal agent like hypertonic saline, Re-aspiration). * **Drug of Choice:** Albendazole. * **Complication:** Rupture of the cyst can lead to fatal **Anaphylaxis**.

Question 409: Lesions caused by Entamoeba histolytica predominantly involve which part of the gastrointestinal tract?

A. Caecum and large intestine (Correct Answer)
B. Duodenum
C. Stomach
D. Jejunum and Ileum

Explanation: **Explanation:** *Entamoeba histolytica* is the causative agent of amoebiasis. The primary site of infection is the **large intestine**, specifically areas where physiological stasis occurs, allowing the parasite more time to invade the mucosa. **1. Why Option A is Correct:** The parasite primarily inhabits the **caecum, ascending colon, and sigmoidorectal region**. These sites are preferred because the fecal stream is slower, facilitating the attachment of trophozoites to the colonic epithelium via galactose-inhibitable adherence lectin. Once attached, the trophozoites secrete cysteine proteases that destroy host tissue, leading to the characteristic **"flask-shaped ulcers"** (narrow neck and broad base). **2. Why Other Options are Incorrect:** * **Option B (Duodenum):** This is the primary site for *Giardia lamblia* and *Strongyloides stercoralis*, not *E. histolytica*. * **Option C (Stomach):** The highly acidic environment of the stomach is hostile to trophozoites. While cysts pass through the stomach, they do not cause lesions there. * **Option D (Jejunum and Ileum):** These are parts of the small intestine. While excystation begins in the terminal ileum, the trophozoites migrate to the large intestine to establish infection. Small bowel involvement is rare in amoebiasis. **NEET-PG High-Yield Pearls:** * **Most common extra-intestinal site:** Liver (Amoebic Liver Abscess), typically involving the **right lobe** (superior-posterior surface). * **Pathognomonic finding:** Presence of **ingested RBCs** (erythrophagocytosis) within the cytoplasm of trophozoites. * **Stool findings:** "Anchovy sauce" appearance of pus in liver abscess; stool in amoebic dysentery is acidic, contains Charcot-Leyden crystals, and shows clumped RBCs. * **Complication:** Amoeboma (a granulomatous mass in the caecum/ascending colon) which can mimic colon cancer.

Question 410: Which parasite causes periporal fibrosis of the liver?

A. Schistosoma japonicum
B. Schistosoma mansoni (Correct Answer)
C. Schistosoma haematobium
D. Schistosoma mekongi

Explanation: **Explanation:** **Schistosoma mansoni** is the primary cause of **Symmers’ pipestem fibrosis** (periportal fibrosis). The pathogenesis involves the deposition of eggs in the presinusoidal capillaries of the liver. These eggs secrete soluble antigens that trigger a chronic granulomatous inflammation. Over time, this leads to extensive collagen deposition around the portal veins (periportal fibrosis) without affecting the liver parenchyma itself. This results in portal hypertension, splenomegaly, and esophageal varices, while liver function tests often remain normal. **Analysis of Options:** * **Schistosoma mansoni (Correct):** Primarily inhabits the inferior mesenteric veins. Its eggs are frequently trapped in the liver, leading to the classic "pipestem" fibrosis. * **Schistosoma japonicum:** While it also causes liver fibrosis and inhabits the superior mesenteric veins, *S. mansoni* is the classic textbook association for Symmers' fibrosis in medical exams. *S. japonicum* often causes more severe, acute disease (Katayama fever). * **Schistosoma haematobium:** Primarily inhabits the vesical venous plexus. It is associated with urinary schistosomiasis, hematuria, and squamous cell carcinoma of the bladder, rather than liver fibrosis. * **Schistosoma mekongi:** Similar to *S. japonicum* but restricted to specific geographical areas (Mekong River basin); it is a less common cause of hepatosplenic disease compared to *S. mansoni*. **NEET-PG High-Yield Pearls:** * **Diagnostic feature:** *S. mansoni* eggs have a characteristic **lateral spine**. * **Intermediate host:** Biomphalaria snail. * **Infective stage:** Cercaria (enters via skin penetration). * **Drug of choice:** Praziquantel for all Schistosoma species.

Practice by Chapter

Classification of Parasites

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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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