Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 451: An examination of sputum for a suspected case of fungal infection may reveal hyphae in which of the following conditions?

A. Aspergillosis (Correct Answer)
B. Sporotrichosis
C. Histoplasmosis
D. Cryptococcosis

Explanation: **Explanation:** The correct answer is **Aspergillosis**. **Why Aspergillosis is correct:** *Aspergillus* species are filamentous fungi characterized by the presence of **septate hyphae** that typically show **dichotomous branching at acute angles (45°)**. In clinical practice, when *Aspergillus* involves the lungs (such as in an Aspergilloma or Invasive Pulmonary Aspergillosis), these characteristic hyphae can be directly visualized in the sputum or bronchoalveolar lavage (BAL) fluid using KOH mounts or silver stains. **Analysis of Incorrect Options:** * **Sporotrichosis:** Caused by *Sporothrix schenckii*, a dimorphic fungus. In tissue or clinical samples (yeast phase), it typically appears as **cigar-shaped budding yeasts**, not hyphae. * **Histoplasmosis:** *Histoplasma capsulatum* is an intracellular dimorphic fungus. In sputum or tissue, it is seen as **small, oval budding yeasts** within macrophages. Hyphae are only seen in the mold form at room temperature in the lab. * **Cryptococcosis:** *Cryptococcus neoformans* is a monomorphic yeast. It is characterized by **spherical, encapsulated budding yeasts**. It never forms true hyphae; its hallmark is the thick polysaccharide capsule visualized by India Ink. **NEET-PG High-Yield Pearls:** * **Aspergillus:** Look for "Acute angle branching" and "Septate hyphae." * **Mucor/Rhizopus:** Look for "Right angle (90°) branching" and "Aseptate/Coenocytic hyphae." * **Dimorphic Fungi Rule:** They exist as **M**old in the **C**old (25°C - hyphae) and **Y**east in the **B**east (37°C/Body - yeast). Since sputum is a clinical sample from the body, you expect the yeast form for *Sporothrix* and *Histoplasma*.

Question 452: What is the most common cause of dysentery in adults?

A. Cryptosporidium
B. Giardia lamblia
C. Strongyloides stercoralis
D. Entamoeba histolytica (Correct Answer)

Explanation: **Explanation:** **Entamoeba histolytica** is the correct answer because it is the primary protozoan parasite responsible for **amoebic dysentery**. The underlying medical concept involves the parasite's ability to produce proteolytic enzymes (like cysteine proteases) that cause tissue lysis, leading to the characteristic **"flask-shaped ulcers"** in the colon. This tissue destruction results in the passage of blood and mucus in stools (dysentery), distinguishing it from simple watery diarrhea. **Analysis of Incorrect Options:** * **Cryptosporidium:** Primarily causes self-limiting, profuse **watery diarrhea** in immunocompetent individuals. It is a major cause of chronic diarrhea in HIV/AIDS patients but does not typically cause dysentery. * **Giardia lamblia:** This parasite inhabits the duodenum and upper jejunum. It causes malabsorption and **steatorrhea** (foul-smelling, fatty stools) rather than dysentery, as it does not invade the intestinal mucosa. * **Strongyloides stercoralis:** While it can cause severe "hyperinfection syndrome" in immunocompromised hosts, its typical presentation involves abdominal pain, dermatitis (larva currens), and respiratory symptoms (Loeffler’s syndrome), not classic dysentery. **High-Yield Clinical Pearls for NEET-PG:** * **Trophozoite Morphology:** Look for the presence of **ingested RBCs** (erythrophagocytosis), which is pathognomonic for *E. histolytica*. * **Quadrinucleated Cyst:** This is the infective stage transmitted via the fecto-oral route. * **Extra-intestinal Amoebiasis:** The most common site is the **Liver (Amoebic Liver Abscess)**, characterized by "anchovy sauce" pus. * **Treatment:** Metronidazole or Tinidazole are the drugs of choice for invasive disease, followed by a luminal amebicide like Diloxanide furoate.

Question 453: What is the average blood loss in ankylostomiasis per worm per day?

A. 0.2 - 0.3 ml/day
B. 2 - 4 ml/day
C. 0.33 - 1 ml/day
D. 0.15 - 0.25 ml/day (Correct Answer)

Explanation: **Explanation:** Ankylostomiasis (Hookworm infection) is a leading cause of iron-deficiency anemia in tropical regions. The blood loss occurs because the adult worms attach to the small intestinal mucosa using their buccal capsules, secreting anticoagulants (like factor Xa inhibitors) to facilitate continuous feeding. **Why Option D is Correct:** The amount of blood loss depends specifically on the species of hookworm. For ***Ancylostoma duodenale*** (Old World hookworm), the average blood loss is **0.15 to 0.25 ml per worm per day**. This species is more pathogenic than *Necator americanus* because it has teeth (rather than cutting plates) and consumes significantly more blood. **Analysis of Incorrect Options:** * **Option A (0.2 - 0.3 ml/day):** This is slightly higher than the standard range cited in major textbooks like Paniker’s Parasitology. * **Option B (2 - 4 ml/day):** This is an extreme overestimate. Such loss would lead to rapid exsanguination and death in heavy infections. * **Option C (0.33 - 1 ml/day):** This range is incorrect for human hookworms; however, it is sometimes confused with the higher blood loss seen in certain animal hookworms. **High-Yield Clinical Pearls for NEET-PG:** * ***Necator americanus* blood loss:** Significantly lower, approximately **0.03 to 0.05 ml per worm per day**. * **Anemia type:** Microcytic hypochromic anemia (Iron deficiency). * **Ground Itch:** The allergic reaction at the site of filariform larvae penetration. * **Löffler's Syndrome:** Can occur during the pulmonary migration phase of the larvae. * **Drug of Choice:** Albendazole (400 mg single dose).

Question 454: A sandfly transmits all of the following diseases EXCEPT?

A. Oriental sore
B. Leishmaniasis
C. Kala-azar
D. Relapsing fever (Correct Answer)

Explanation: **Explanation:** The correct answer is **Relapsing fever** because it is not transmitted by the sandfly (*Phlebotomus* species). Relapsing fever is caused by *Borrelia* species and is transmitted by either the **body louse** (*Pediculus humanus corporis*), which causes Epidemic Relapsing Fever, or **soft ticks** (*Ornithodoros*), which cause Endemic Relapsing Fever. **Analysis of Options:** * **Oriental sore (Option A):** Also known as Cutaneous Leishmaniasis, it is caused by *Leishmania tropica* and is transmitted by the bite of an infected female sandfly. * **Leishmaniasis (Option B):** This is the umbrella term for diseases caused by *Leishmania* parasites. All forms (Cutaneous, Mucocutaneous, and Visceral) are transmitted via the sandfly vector. * **Kala-azar (Option C):** Also known as Visceral Leishmaniasis, it is caused by *Leishmania donovani*. In India, the specific vector is the sandfly ***Phlebotomus argentipes***. **High-Yield Clinical Pearls for NEET-PG:** * **Sandfly Characteristics:** They are small, moth-like flies that fly in short hops and are nocturnal. Only the **female** sandfly takes a blood meal. * **Other diseases transmitted by Sandfly:** Sandfly fever (Pappataci fever) and Oroya fever (Bartonellosis). * **Infective Stage:** For Leishmaniasis, the sandfly injects the **promastigote** stage into the human host. * **Vector Control:** Sandflies are highly susceptible to DDT residual spraying, which is a mainstay in Kala-azar elimination programs.

Question 455: Visceral larva migrans is a feature of which of the following?

A. Ancyclostoma caninum
B. Ancyclostoma braziliense
C. Toxocara canis (Correct Answer)
D. Ancyclostoma duodenale

Explanation: **Explanation:** **Toxocara canis** is the primary causative agent of **Visceral Larva Migrans (VLM)**. This condition occurs when humans (accidental hosts) ingest embryonated eggs of dog roundworms (*T. canis*) or cat roundworms (*T. cati*). Because humans are not the definitive hosts, the larvae cannot mature into adult worms. Instead, they penetrate the intestinal wall and migrate aimlessly through internal organs—most commonly the **liver, lungs, and eyes** (Ocular Larva Migrans)—causing inflammatory reactions and peripheral eosinophilia. **Analysis of Incorrect Options:** * **Options A & B (Ancyclostoma caninum and A. braziliense):** These are the dog and cat hookworms, respectively. They cause **Cutaneous Larva Migrans (Creeping Eruption)**. The larvae penetrate the skin but lack the collagenase required to breach the basement membrane, confining the migration to the subcutaneous tissue rather than internal organs. * **Option D (Ancyclostoma duodenale):** This is the human hookworm. It completes its life cycle in humans, maturing into adult worms in the small intestine, and does not cause the "larva migrans" syndrome seen with animal parasites. **NEET-PG High-Yield Pearls:** * **Diagnosis:** VLM is characterized by a triad of **hypereosinophilia, hepatomegaly, and hypergammaglobulinemia**. * **Serology:** ELISA using **Excretory-Secretory (ES) antigens** is the gold standard for diagnosis. * **Treatment:** Albendazole is the drug of choice. * **Key Distinction:** Remember: **C**utaneous = **C**at/dog hookworm; **V**isceral = **V**ery large roundworm (*Toxocara*).

Question 456: All of the following are true about amoebiasis except?

A. Flask-shaped ulcers
B. Disease affects the caecum and ascending colon
C. Anchovy pus in the liver
D. Coagulative necrosis (Correct Answer)

Explanation: **Explanation:** The correct answer is **D (Coagulative necrosis)** because *Entamoeba histolytica* characteristically causes **liquefactive necrosis**, not coagulative. The parasite releases proteolytic enzymes (histolysins) and pore-forming proteins (amoebapores) that dissolve host tissues, leading to a liquid, necrotic mass. Coagulative necrosis is typically associated with ischemia (infarction) in solid organs. **Analysis of other options:** * **A. Flask-shaped ulcers:** This is the classic pathological hallmark of intestinal amoebiasis. The parasite penetrates the mucosal layer and spreads laterally in the submucosa, creating an ulcer with a narrow neck and a broad base. * **B. Disease affects the caecum and ascending colon:** These are the most common sites for intestinal amoebiasis because the slow transit of fecal matter in the large intestine allows the trophozoites more time to colonize and invade the mucosa. * **C. Anchovy pus in the liver:** This refers to the characteristic appearance of an Amoebic Liver Abscess (ALA) aspirate. It is a sterile, odorless, reddish-brown fluid composed of liquefied hepatocytes and blood, resembling anchovy sauce. **NEET-PG High-Yield Pearls:** * **Diagnostic Gold Standard:** Stool microscopy for **quadrinucleate cysts** (chronic/carrier) or **trophozoites with ingested RBCs** (active dysentery). * **Liver Abscess:** Usually occurs in the **right lobe** (due to portal blood flow) and is "sterile" (trophozoites are found in the abscess wall, not the pus). * **Treatment:** Metronidazole/Tinidazole for tissue stages; Diloxanide furoate or Paromomycin for luminal stages (to prevent relapse).

Question 457: Which of the following parasites requires three hosts in its life cycle?

A. Taenia solium
B. Entamoeba histolytica
C. Trichuris trichiura
D. Diphyllobothrium latum (Correct Answer)

Explanation: **Explanation:** The correct answer is **Diphyllobothrium latum** (the Fish Tapeworm). This parasite is unique among common human helminths because it requires **three different hosts** to complete its complex life cycle: 1. **First Intermediate Host:** A freshwater crustacean (*Cyclops*), which ingests the ciliated larva (coracidium). 2. **Second Intermediate Host:** Freshwater fish (e.g., pike, trout), which ingest the *Cyclops* and develop the infective **plerocercoid larva**. 3. **Definitive Host:** Humans (or other fish-eating mammals), who ingest undercooked fish containing the plerocercoid larva. **Why the other options are incorrect:** * **Taenia solium (Pork Tapeworm):** Requires **two hosts**—Humans (Definitive) and Pigs (Intermediate). * **Entamoeba histolytica:** Requires only **one host** (Humans). It is a protozoan transmitted via the fecal-oral route (monoxenous life cycle). * **Trichuris trichiura (Whipworm):** Requires only **one host** (Humans). It is a soil-transmitted helminth with no intermediate host. **High-Yield Clinical Pearls for NEET-PG:** * **Vitamin B12 Deficiency:** *D. latum* competes with the host for Vitamin B12 absorption in the jejunum, leading to **Megaloblastic Anemia** (resembling Pernicious Anemia). * **Operculated Eggs:** It is the only human tapeworm that produces operculated eggs (similar to trematodes) and lacks a rostellum/hooks. * **Diagnosis:** Identification of characteristic operculated eggs or proglottids (with a "rosette-shaped" uterus) in stool. * **Treatment:** Praziquantel is the drug of choice.

Question 458: Taenia saginata (beef tapeworm) causes less serious infection than Taenia solium (pork tapeworm) because:

A. Acute intestinal blockage is less common in beef tapeworm infection.
B. Unlike T. saginata, T. solium produces neurocysticercosis, which results in serious lesions in humans due to toxic byproducts formed. (Correct Answer)
C. Larval invasion does not occur in beef tapeworm infection.
D. The adult beef tapeworms are smaller.

Explanation: ### Explanation The clinical severity of *Taenia* infections depends on whether the human acts as the **definitive host** (harboring the adult worm) or the **accidental intermediate host** (harboring the larvae). **1. Why Option B is Correct:** In *Taenia saginata* (beef tapeworm) infection, humans are strictly definitive hosts; we ingest **cysticerci** in undercooked beef, resulting only in intestinal taeniasis (usually asymptomatic or mild). However, in *Taenia solium* (pork tapeworm), humans can serve as both definitive and intermediate hosts. If a human ingests *T. solium* **eggs** (via feco-oral route or autoinfection), the eggs hatch into oncospheres that migrate to tissues, forming **Cysticercus cellulosae**. When these larvae lodge in the brain, it causes **Neurocysticercosis (NCC)**—the most common cause of adult-onset seizures worldwide. The inflammatory response to dying larvae and their metabolic byproducts causes significant neurological morbidity, making *T. solium* far more dangerous. **2. Analysis of Incorrect Options:** * **Option A:** Intestinal blockage is rare for both, but *T. saginata* is actually larger and more muscular, making it theoretically more likely to cause mechanical issues, though this is not the primary reason for the difference in severity. * **Option C:** While it is true that larval invasion (cysticercosis) does not occur in *T. saginata* infection, the option is less complete than B, which specifies the clinical consequence (NCC). * **Option D:** Incorrect. *T. saginata* (5–10 meters) is significantly **larger** than *T. solium* (2–4 meters). **High-Yield NEET-PG Pearls:** * **Intermediate Host:** Cow for *T. saginata*; Pig/Human for *T. solium*. * **Diagnostic Morphological Difference:** *T. saginata* has **15–30** lateral uterine branches (dichotomous); *T. solium* has **7–13** (dendritic). * **Scolex:** *T. saginata* is unarmed (no hooks); *T. solium* has a rostellum with hooks. * **Treatment:** Praziquantel is the drug of choice for intestinal taeniasis; Albendazole + Steroids are used for NCC.

Question 459: What is the investigation of choice for invasive amebiasis?

A. Indirect heamagglutination
B. ELISA (Correct Answer)
C. Counter immune electrophoresis
D. Microscopy

Explanation: **Explanation:** Invasive amebiasis (liver abscess or invasive colitis) occurs when *Entamoeba histolytica* trophozoites breach the intestinal mucosa and enter the bloodstream. In these cases, **ELISA (Enzyme-Linked Immunosorbent Assay)** is the investigation of choice because it offers high sensitivity (up to 95%) and specificity for detecting serum antibodies or specific antigens. * **Why ELISA is correct:** It is the modern gold standard for diagnosing extra-intestinal amebiasis. It can detect **Gal/GalNAc lectin antigen** in pus or stool (indicating active infection) or anti-amebic antibodies in the serum. In endemic areas, antigen detection is preferred to differentiate between past exposure and current invasive disease. **Analysis of Incorrect Options:** * **Indirect Hemagglutination (IHA):** While highly sensitive for liver abscesses, it is an older technique that is technically demanding and has largely been replaced by ELISA in clinical practice. * **Counter Immune Electrophoresis (CIEP):** This was historically used for rapid results but lacks the sensitivity and quantitative capabilities of ELISA. * **Microscopy:** While the gold standard for **intestinal** amebiasis (identifying quadrinucleate cysts or trophozoites with ingested RBCs), it is often negative in **invasive** cases like liver abscesses, as the pus (anchovy sauce) rarely contains the parasite. **High-Yield Clinical Pearls for NEET-PG:** * **Anchovy Sauce Pus:** Characteristic of Amoebic Liver Abscess (ALA); it is odorless and consists of necrotic hepatocytes. * **Trophozoites with ingested RBCs:** Pathognomonic for *E. histolytica* (distinguishes it from non-pathogenic *E. dispar*). * **Treatment:** Metronidazole is the drug of choice for invasive disease, followed by a luminal amebicide (e.g., Diloxanide furoate) to eradicate the carrier state.

Question 460: What is the primary purpose of preparing a thick peripheral blood smear (PBS)?

A. Identifying parasite species
B. Assessing parasite prevalence (Correct Answer)
C. Both identifying parasite species and assessing prevalence
D. None of the above

Explanation: In parasitology, particularly for diagnosing malaria, two types of peripheral blood smears (PBS) are used: **Thick** and **Thin** smears. ### Why Option B is Correct The primary purpose of a **thick smear** is **screening and quantification**. In a thick smear, a larger volume of blood (approximately 3 layers of RBCs) is concentrated in a small area. The RBCs are lysed during the staining process (dehemoglobinization), leaving behind concentrated parasites. This makes it roughly **20 to 40 times more sensitive** than a thin smear, allowing clinicians to detect low levels of parasitemia and assess the overall **parasite prevalence** (presence and density) in the patient. ### Why Other Options are Incorrect * **Option A (Identifying species):** This is the primary role of the **thin smear**. In a thin smear, the RBC morphology is preserved (fixed with methanol). This allows for the observation of species-specific characteristics, such as Schüffner’s dots, the shape of the gametocyte, or the size of the infected RBC. * **Option C:** While both smears are often performed together on one slide, their individual primary purposes are distinct. The thick smear screens for "if" the parasite is there, and the thin smear identifies "which" species it is. ### High-Yield NEET-PG Pearls * **Gold Standard:** The combination of thick and thin Giemsa-stained smears remains the gold standard for malaria diagnosis. * **Stain of Choice:** Giemsa stain is preferred over Leishman stain for better visualization of stippling. * **Fixation:** Thin smears are fixed with **absolute ethyl alcohol or methanol**; thick smears are **never fixed** (to allow for RBC lysis). * **Sensitivity:** A thick smear can detect as few as 5–10 parasites per microliter of blood.

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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