Parasitology Practice Questions

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

Plasmodium falciparum. **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).

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

Trombiculid mite. **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).

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

None of the above. ### 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).

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

Paragonimus westermani. ### 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.

Q: Hydatid disease is caused by which organism?

Echinococcus. **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**.

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

Caecum and large intestine. **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.

Q: Which parasite causes periporal fibrosis of the liver?

Schistosoma mansoni. **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.

Question 1

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

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium malariae

Answer

Plasmodium vivax

Answer

Plasmodium ovale

Question 2

Which of the following statements regarding cysticercosis is FALSE?

Accepted Answer

Commonest sites are meninges and cerebral ventricles.

Answer

Calcification is common.

Answer

It causes focal neurological complications.

Answer

It is found in subcutaneous tissues.

Question 3

Which of the following is a vector for scrub typhus?

Accepted Answer

Trombiculid mite

Answer

Louse

Answer

Tick

Answer

Reduviid bug

Question 4

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

Accepted Answer

None of the above

Answer

Merozoite

Answer

Sporozoite

Answer

Trophozoite

Question 5

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

Accepted Answer

Paragonimus westermani

Answer

Clonorchis sinensis

Answer

Opisthorchis viverrini

Answer

Diphyllobothrium latum

Question 6

Which of the following statements is true about hard ticks?

Accepted Answer

All of the above.

Answer

They have four stages in their life cycle.

Answer

The female tick lays thousands of eggs.

Answer

The larval stage is known as seed ticks.

Question 7

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

Accepted Answer

E. coli

Answer

E. histolytica

Answer

Acanthamoeba

Answer

E. hamanni

Question 8

Hydatid disease is caused by which organism?

Accepted Answer

Echinococcus

Answer

Tapeworm

Answer

Ascaris

Answer

Hookworm

Question 9

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

Accepted Answer

Caecum and large intestine

Answer

Duodenum

Answer

Stomach

Answer

Jejunum and Ileum

Question 10

Which parasite causes periporal fibrosis of the liver?

Accepted Answer

Schistosoma mansoni

Answer

Schistosoma japonicum

Answer

Schistosoma haematobium

Answer

Schistosoma mekongi

Parasitology — MCQs

Parasitology — MCQs

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