Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 391: Which of the following parasites is NOT transmitted by fish?

A. Paragonimus westermanii
B. Clonorchis sinensis
C. Diphyllobothrium latum
D. Schistosoma japonicum (Correct Answer)

Explanation: The correct answer is **D. Schistosoma japonicum**. ### **Explanation** The transmission of parasites depends on their specific life cycle and the intermediate host involved. 1. **Why Schistosoma japonicum is the correct answer:** Unlike the other options, *Schistosoma* species (Blood flukes) do not require a second intermediate host like fish or crabs. Transmission occurs via **direct skin penetration** by **cercariae** swimming freely in contaminated water. The intermediate host for *Schistosoma* is always a **snail** (e.g., *Oncomelania* for *S. japonicum*). 2. **Why the other options are incorrect:** * **Clonorchis sinensis (Chinese Liver Fluke):** Transmission occurs by ingesting undercooked or raw **freshwater fish** containing encysted metacercariae. * **Diphyllobothrium latum (Fish Tapeworm):** This is the largest tapeworm infecting humans. It is transmitted by eating raw or undercooked **freshwater fish** containing plerocercoid larvae. * **Paragonimus westermanii (Oriental Lung Fluke):** While primarily associated with **crabs and crayfish**, it is often grouped with aquatic-borne trematodes. In many contexts, "fish-borne" is used broadly for aquatic intermediate hosts, but specifically, *Schistosoma* is the only one here that bypasses an edible aquatic host entirely. ### **High-Yield Clinical Pearls for NEET-PG** * **Diphyllobothrium latum:** Classically associated with **Vitamin B12 deficiency** and megaloblastic anemia because the worm competes for B12 absorption in the ileum. * **Schistosoma japonicum:** Known for causing "Katayama fever" and can lead to portal hypertension and cirrhosis. It resides in the **superior mesenteric veins**. * **Infective Stages:** * *Schistosoma*: Cercaria (Skin penetration). * *Clonorchis/Paragonimus*: Metacercaria (Ingestion). * *D. latum*: Plerocercoid larva (Ingestion).

Question 392: Which of the following organisms does not have a cyst phase?

A. Gardenella vaginalis (Correct Answer)
B. Trichomonas vaginalis
C. Entamoeba hystolytica
D. Entamoeba coli

Explanation: **Explanation:** The correct answer is **A. *Gardnerella vaginalis***. The underlying medical concept here is the distinction between **protozoa** and **bacteria**. *Gardnerella vaginalis* is a gram-variable anaerobic bacterium associated with bacterial vaginosis. As a bacterium, it does not undergo a life cycle involving trophozoite and cyst stages; instead, it exists only as a vegetative bacterial cell. **Analysis of Options:** * **Trichomonas vaginalis (Option B):** While this is a protozoan, it is unique because it **does not have a cyst stage**. It exists only in the trophozoite form and is transmitted directly via sexual contact. However, in the context of this specific question, *Gardnerella* is the "most correct" answer because it is not even a parasite/protozoan. (Note: In many exams, if *Gardnerella* were not an option, *Trichomonas* would be the classic answer for a parasite lacking a cyst phase). * **Entamoeba histolytica (Option C):** This is an intestinal amoeba that has both a motile **trophozoite** stage (causing disease) and a resistant **quadrinucleate cyst** stage (responsible for transmission via the fecal-oral route). * **Entamoeba coli (Option D):** A non-pathogenic intestinal commensal that also possesses both trophozoite and cyst stages (the mature cyst typically has 8 nuclei). **NEET-PG High-Yield Pearls:** * **Parasites with NO cyst stage:** *Trichomonas vaginalis*, *Entamoeba gingivalis*, and *Dientamoeba fragilis* (though the latter is debated). * **Gardnerella vaginalis:** Look for **"Clue Cells"** (epithelial cells covered in bacteria) and a positive **Whiff test** (amine odor with KOH) on vaginal discharge microscopy. * **Infective stage:** For most intestinal protozoa, the **mature cyst** is the infective form, while the trophozoite is the pathogenic form.

Question 393: Rhabditiform larvae in freshly passed stools are seen with which of the following parasites?

A. Toxoplasma
B. Trichuris
C. Ankylostoma
D. Strongyloides (Correct Answer)

Explanation: **Explanation:** The presence of **Rhabditiform larvae** in freshly passed stool is the diagnostic hallmark of ***Strongyloides stercoralis***. Unlike most intestinal nematodes where eggs are the primary diagnostic stage in feces, *Strongyloides* eggs usually hatch within the intestinal mucosa. Therefore, the first-stage (L1) rhabditiform larvae are passed in the stool. **Why the other options are incorrect:** * **Toxoplasma gondii:** This is a protozoan, not a helminth. Diagnosis is typically via serology or PCR; it does not produce larvae in human stool. * **Trichuris trichiura (Whipworm):** Diagnosis is made by identifying characteristic **barrel-shaped eggs** with bipolar plugs in the stool. Larvae are not seen in fresh samples. * **Ankylostoma duodenale (Hookworm):** Hookworms typically pass **non-bile stained, segmented eggs** in the stool. While rhabditiform larvae can develop from these eggs, this only occurs if the stool sample is left at room temperature for 24–48 hours; they are not found in *freshly* passed stool. **High-Yield NEET-PG Pearls:** * **Auto-infection:** *Strongyloides* is unique because rhabditiform larvae can transform into infective filariform larvae within the colon, leading to internal auto-infection. * **Hyperinfection Syndrome:** In immunocompromised patients (especially those on steroids), this cycle accelerates, leading to massive larval dissemination. * **Morphology:** *Strongyloides* rhabditiform larvae have a **short buccal capsule** and a prominent genital primordium, distinguishing them from Hookworm larvae (which have a long buccal capsule). * **Culture:** If stool microscopy is negative but suspicion is high, **Agar plate culture** (Koga agar) is the most sensitive method.

Question 394: Katayama fever is caused by which of the following parasites?

A. Fasciola hepatica
B. Clonorchis sinensis
C. Schistosoma mansoni (Correct Answer)
D. Ascaris lumbricoides

Explanation: **Explanation:** **Katayama fever** is an acute clinical manifestation of **Schistosomiasis** (specifically *S. mansoni* and *S. japonicum*). It is a systemic hypersensitivity reaction (Type III) to the antigens released by migrating schistosomulae and the onset of egg-laying. **Why Schistosoma mansoni is correct:** When the cercariae penetrate the skin and mature into adults, they release eggs that trigger a massive immune response. This typically occurs 2–8 weeks after exposure. Clinical features include high-grade fever, chills, lymphadenopathy, hepatosplenomegaly, and significant **eosinophilia**. **Why the other options are incorrect:** * **Fasciola hepatica (Sheep liver fluke):** Causes "Liver Rot." While it can cause fever and eosinophilia during the hepatic migration phase, it is not associated with Katayama syndrome. * **Clonorchis sinensis (Chinese liver fluke):** Primarily associated with biliary tract inflammation and is a major risk factor for **Cholangiocarcinoma**. * **Ascaris lumbricoides:** Causes **Loeffler’s syndrome** (transient pulmonary infiltrates with eosinophilia) during the larval migration phase through the lungs, but not Katayama fever. **High-Yield Clinical Pearls for NEET-PG:** * **Infective stage:** Cercaria (penetrates skin during swimming/wading in fresh water). * **Diagnostic stage:** Non-operculated eggs with a **lateral spine** (*S. mansoni*) or **terminal spine** (*S. haematobium*). * **S. haematobium association:** Strongly linked to **Squamous Cell Carcinoma of the urinary bladder**. * **Drug of Choice:** Praziquantel is the gold standard for all Schistosoma species.

Question 395: Opisthorchis sinensis can cause which of the following malignancies?

A. Cholangiocarcinoma (Correct Answer)
B. Hepatocellular carcinoma
C. Pancreatic carcinoma
D. All of the above

Explanation: **Explanation:** **Opisthorchis sinensis** (also known as *Clonorchis sinensis* or the Chinese Liver Fluke) is a trematode that primarily inhabits the **distal bile ducts**. The chronic infection leads to mechanical irritation, localized inflammation, and the release of mitogenic excretory-secretory products. This chronic inflammatory milieu induces adenomatous hyperplasia and cellular dysplasia, which are precursors to **Cholangiocarcinoma** (bile duct cancer). Consequently, the IARC classifies it as a Group 1 carcinogen. **Analysis of Options:** * **A. Cholangiocarcinoma (Correct):** The fluke resides in the biliary tree, causing chronic biliary inflammation and fibrosis, which directly leads to malignancy of the bile duct epithelium. * **B. Hepatocellular Carcinoma (Incorrect):** While *C. sinensis* affects the liver, HCC arises from hepatocytes. HCC is primarily associated with Hepatitis B, Hepatitis C, and Aflatoxin B1, not liver flukes. * **C. Pancreatic Carcinoma (Incorrect):** Although the fluke can occasionally migrate to the pancreatic duct causing pancreatitis, it is not a recognized primary cause of pancreatic malignancy. **High-Yield Clinical Pearls for NEET-PG:** * **Intermediate Hosts:** 1st host is the Snail (*Parafossarulus*); 2nd host is the Cyprinoid fish. * **Infective Stage:** Metacercariae (found in undercooked/raw fish). * **Diagnosis:** Stool microscopy showing characteristic "operculated eggs with a small abopercular knob" (often described as "light bulb" shaped). * **Drug of Choice:** Praziquantel. * **Other Flukes & Cancer:** *Schistosoma haematobium* is famously associated with **Squamous Cell Carcinoma of the Urinary Bladder**.

Question 396: All the following are true about Naegleria fowleri EXCEPT?

A. Causes primary amoebic meningoencephalitis
B. Also called the brain-eating amoeba
C. Infective form is trophozoites
D. Clinical course is subacute to chronic (Correct Answer)

Explanation: **Explanation:** *Naegleria fowleri* is a free-living thermophilic amoeba found in warm freshwater bodies. The correct answer is **Option D** because the clinical course of *Naegleria fowleri* is **hyperacute and rapidly fatal**, not subacute or chronic. **1. Why Option D is the correct (False) statement:** *Naegleria fowleri* causes **Primary Amoebic Meningoencephalitis (PAM)**. The disease progresses aggressively, with death usually occurring within 7 to 10 days of symptom onset. In contrast, a subacute or chronic course is characteristic of **Granulomatous Amoebic Encephalitis (GAE)**, caused by *Acanthamoeba* or *Balamuthia mandrillaris*, typically seen in immunocompromised hosts. **2. Analysis of other options:** * **Option A:** True. PAM is the specific clinical entity caused by *N. fowleri*, characterized by rapid destruction of brain tissue. * **Option B:** True. It is popularly known as the "brain-eating amoeba" due to its ability to migrate via the olfactory neuroepithelium and digest brain parenchyma. * **Option C:** True. While the amoeba exists in three stages (cyst, flagellate, and trophozoite), the **trophozoite** is the only stage found in human tissue and is the infective form that enters the nasal mucosa. **High-Yield Clinical Pearls for NEET-PG:** * **Route of Entry:** Cribriform plate (via inhalation of contaminated water during swimming/diving). * **Diagnosis:** Wet mount of CSF shows **motile trophozoites**. (Note: Cysts are never seen in brain tissue/CSF in *Naegleria* infections). * **Drug of Choice:** Amphotericin B (often used in combination with Miltefosine). * **Key Differentiator:** Unlike *Acanthamoeba*, *Naegleria* affects previously healthy, immunocompetent children and young adults.

Question 397: In Culex mosquitoes, what is the type of biological transmission for filarial parasites?

A. Cyclo-developmental (Correct Answer)
B. Cyclo-propagative
C. Propagative
D. Cyclical

Explanation: ### Explanation In medical parasitology, biological transmission occurs when an infectious agent undergoes biological changes or multiplication within a vector. The correct answer is **Cyclo-developmental** because of the specific life cycle of *Wuchereria bancrofti* within the *Culex* mosquito. **1. Why Cyclo-developmental is Correct:** In this type of transmission, the parasite undergoes **essential developmental changes** (e.g., from Microfilaria to L1, L2, and finally the infective L3 stage) but **does not multiply** in numbers. One microfilaria ingested by the mosquito results in only one infective larva. This is the hallmark of filarial parasites (*Wuchereria, Brugia*). **2. Analysis of Incorrect Options:** * **Propagative (C):** The parasite undergoes **multiplication only**, with no change in form or stage. Example: Plague bacilli in rat fleas. * **Cyclo-propagative (B):** The parasite undergoes **both** developmental changes and multiplication. Example: *Plasmodium* (Malaria) in *Anopheles* mosquitoes or *Leishmania* in sandflies. * **Cyclical (D):** This is a general term often used interchangeably with cyclo-developmental but is less specific in a technical NEET-PG context. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vector for Bancroftian Filariasis:** *Culex quinquefasciatus* (breeds in dirty/stagnant water). * **Infective Stage:** The **L3 (filariform) larva** is the stage infective to humans. * **Diagnostic Stage:** Microfilaria (found in peripheral blood during nocturnal periodicity, usually 10 PM – 2 AM). * **Key Distinction:** Remember—**Malaria = Cyclo-propagative** (numbers increase); **Filariasis = Cyclo-developmental** (numbers stay the same, only stages change).

Question 398: A 24-year-old patient with AIDS presents with chronic abdominal pain, low-grade fever, diarrhea, and malabsorption. Oocysts are demonstrated in the stool. What is the likely cause of his diarrhea?

A. E. histolytica
B. G. lamblia
C. Microsporidia
D. Isospora belli (Correct Answer)

Explanation: **Explanation:** The clinical presentation of chronic diarrhea, malabsorption, and fever in an HIV/AIDS patient, combined with the presence of **oocysts** in the stool, points directly to **Cystoisospora belli** (formerly *Isospora belli*). **1. Why Isospora belli is correct:** *Isospora belli* is an opportunistic protozoan that causes severe, watery, non-bloody diarrhea in immunocompromised individuals. It is unique among the common AIDS-related coccidia because it produces large, oval-shaped oocysts (approx. 25–30 µm) that are visible on modified acid-fast staining. It typically involves the small intestine, leading to malabsorption and weight loss. **2. Why other options are incorrect:** * **E. histolytica:** Causes amoebic dysentery (bloody diarrhea) and liver abscesses. It is identified by **cysts or trophozoites**, not oocysts. * **G. lamblia:** Causes foul-smelling, fatty stools (steatorrhea) but is not specifically an opportunistic infection of AIDS. It is identified by **cysts or pear-shaped trophozoites**. * **Microsporidia:** While a common cause of chronic diarrhea in AIDS, Microsporidia are **spores**, not oocysts. They are much smaller (1–2 µm) and usually require special stains like Chromotrope 2R. **High-Yield Clinical Pearls for NEET-PG:** * **Staining:** *Isospora*, *Cryptosporidium*, and *Cyclospora* are all **Acid-Fast positive**. * **Treatment:** Unlike *Cryptosporidium* (which is difficult to treat), *Isospora belli* responds excellently to **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. * **Morphology:** *Isospora* oocysts are the largest among the coccidia; *Cryptosporidium* oocysts are the smallest (4–5 µm) and spherical. * **Autofluorescence:** *Isospora* and *Cyclospora* oocysts exhibit blue-green autofluorescence under UV microscopy.

Question 399: Kala azar is defined as:

A. Mucocutaneous leishmaniasis
B. Cutaneous leishmaniasis
C. Oriental sore
D. Visceral leishmaniasis (Correct Answer)

Explanation: **Explanation:** **Kala-azar**, also known as "Black Fever" or "Dum-dum fever," is the clinical manifestation of **Visceral Leishmaniasis (VL)**. It is caused by the protozoan parasite *Leishmania donovani* and is transmitted by the bite of the infected female sandfly (*Phlebotomus argentipes*). The term "Kala-azar" is derived from Hindi, referring to the characteristic hyperpigmentation of the skin seen in Indian patients. * **Why Option D is correct:** Visceral leishmaniasis is a systemic disease where the parasite disseminates to the reticuloendothelial system, primarily affecting the **liver, spleen, and bone marrow**. This leads to the classic triad of prolonged fever, massive splenomegaly, and pancytopenia. * **Why Options A, B, and C are incorrect:** * **Cutaneous Leishmaniasis (B)** and **Oriental Sore (C)** refer to localized skin ulcers caused by species like *L. tropica* or *L. major*. * **Mucocutaneous Leishmaniasis (A)** involves the destruction of nasopharyngeal mucosa, typically caused by the *L. braziliensis* complex (New World Leishmaniasis). **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Phlebotomus argentipes* (Sandfly). * **Diagnostic Gold Standard:** Demonstration of **LD bodies** (Amastigotes) in bone marrow or splenic aspirates. * **Serology:** **rK39 antigen** strip test is the rapid diagnostic test of choice. * **Drug of Choice:** **Liposomal Amphotericin B** is currently the first-line treatment. * **PKDL (Post Kala-azar Dermal Leishmaniasis):** A non-ulcerative skin condition that develops in a percentage of cured VL patients, acting as a reservoir for the parasite.

Question 400: Fairley's test is used for the diagnosis of which condition?

A. Cysticercosis
B. Lymphogranuloma venereum
C. Schistosomiasis (Correct Answer)
D. Filariasis

Explanation: **Explanation:** **Fairley’s Test** is a skin hypersensitivity test used for the diagnosis of **Schistosomiasis** (Bilharziasis). It is an intradermal test that utilizes an antigen extracted from the cercariae of *Schistosoma spindale* (a cattle schistosome). A positive reaction is indicated by the development of a wheal and flare at the injection site within 15–20 minutes, signifying an immediate type (Type I) hypersensitivity reaction. While it is highly sensitive, it lacks specificity as it can cross-react with other trematode infections. **Analysis of Incorrect Options:** * **Cysticercosis:** Diagnosed primarily via neuroimaging (CT/MRI) and serology (Enzyme-linked immunoelectrotransfer blot - EITB). The **Casoni test** is a similar skin test, but it is specific to Hydatid disease (*Echinococcus granulosus*), not cysticercosis. * **Lymphogranuloma venereum (LGV):** Historically diagnosed using the **Frei test**, which is an intradermal test using the *Chlamydia trachomatis* antigen. * **Filariasis:** Diagnosis relies on the demonstration of microfilariae in peripheral blood (nocturnal smear) or the **DEC provocation test**. While skin tests exist for filariasis (using *Dirofilaria immitis* antigen), Fairley’s test is specific to Schistosomiasis. **High-Yield Clinical Pearls for NEET-PG:** * **Schistosomiasis:** Look for "Swimmer’s itch" (cercarial dermatitis) and "Katayama fever" in clinical vignettes. * **Diagnostic Gold Standard:** Microscopic detection of characteristic eggs in urine (*S. haematobium* - terminal spine) or feces (*S. mansoni* - lateral spine; *S. japonicum* - rudimentary spine). * **Drug of Choice:** Praziquantel is the treatment of choice for all species of Schistosoma.

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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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