Parasitology Practice Questions

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

Schistosoma japonicum. 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).

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

Strongyloides. **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.

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

Schistosoma mansoni. **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.

Q: Opisthorchis sinensis can cause which of the following malignancies?

Cholangiocarcinoma. **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**.

Q: All the following are true about Naegleria fowleri EXCEPT?

Clinical course is subacute to chronic. **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.

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

Cyclo-developmental. ### 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).

Q: 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?

Isospora belli. **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.

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: 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

Which of the following parasites is NOT transmitted by fish?

Accepted Answer

Schistosoma japonicum

Answer

Paragonimus westermanii

Answer

Clonorchis sinensis

Answer

Diphyllobothrium latum

Question 2

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

Accepted Answer

Strongyloides

Answer

Toxoplasma

Answer

Trichuris

Answer

Ankylostoma

Question 3

Katayama fever is caused by which of the following parasites?

Accepted Answer

Schistosoma mansoni

Answer

Fasciola hepatica

Answer

Clonorchis sinensis

Answer

Ascaris lumbricoides

Question 4

Opisthorchis sinensis can cause which of the following malignancies?

Accepted Answer

Cholangiocarcinoma

Answer

Hepatocellular carcinoma

Answer

Pancreatic carcinoma

Answer

All of the above

Question 5

All the following are true about Naegleria fowleri EXCEPT?

Accepted Answer

Clinical course is subacute to chronic

Answer

Causes primary amoebic meningoencephalitis

Answer

Also called the brain-eating amoeba

Answer

Infective form is trophozoites

Question 6

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

Accepted Answer

Cyclo-developmental

Answer

Cyclo-propagative

Answer

Propagative

Answer

Cyclical

Question 7

An HIV patient presented with diarrhea. On stool examination, acid-fast organisms were seen. What is the drug of choice for this patient?

Accepted Answer

TMP-SMX

Answer

Nitazoxanide

Answer

Primaquine

Answer

Niclosamide

Question 8

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?

Accepted Answer

Isospora belli

Answer

E. histolytica

Answer

G. lamblia

Answer

Microsporidia

Question 9

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 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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