Parasitology Practice Questions

Q: A patient with AIDS experienced an acute episode of diarrhea. Stool examination revealed an oval structure, 8 to 9 micrometers in diameter, that was acid-fast and fluoresced blue under ultraviolet light. What is the most likely identification of this organism?

Cyclospora. **Explanation:** The clinical presentation of acute diarrhea in an immunocompromised (AIDS) patient, combined with specific morphologic and staining characteristics, points directly to **Cyclospora cayetanensis**. **Why Cyclospora is correct:** The key diagnostic features provided are: 1. **Size:** Cyclospora oocysts are typically **8–10 μm** in diameter (twice the size of *Cryptosporidium*). 2. **Staining:** They are **variably acid-fast** (some stain pink/red, others remain ghost-like). 3. **Autofluorescence:** This is the pathognomonic "clincher" for NEET-PG. Under UV light (330–365 nm), Cyclospora oocysts exhibit **intense blue/green autofluorescence** due to the presence of phenolic compounds in the oocyst wall. **Why other options are incorrect:** * **Cryptosporidium:** While also acid-fast and common in AIDS, the oocysts are significantly smaller (**4–6 μm**) and **do not** exhibit autofluorescence. * **Enterocytozoon (Microsporidia):** These are much smaller (1–3 μm) and are not acid-fast; they require specialized stains like Modified Trichrome or Calcofluor White. * **Giardia:** These are flagellated protozoa (cysts are 8–12 μm) but are **not acid-fast** and do not fluoresce. They typically present with foul-smelling, fatty stools (steatorrhea). **High-Yield Clinical Pearls for NEET-PG:** * **Size Comparison:** *Cryptosporidium* (4–6 μm) < *Cyclospora* (8–10 μm) < *Isospora/Cystoisospora* (25–30 μm). * **Treatment:** Unlike *Cryptosporidium* (Nitazoxanide), *Cyclospora* is treated with **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. * **Transmission:** Often associated with contaminated imported soft fruits (raspberries, strawberries) and leafy vegetables.

Q: What causes swollen belly syndrome?

Strongyloides fuelleborni. **Explanation:** **Strongyloides fuelleborni** is the causative agent of **Swollen Belly Syndrome (SBS)**, a specific clinical entity primarily reported in infants in Papua New Guinea and parts of Africa. **Why it is the correct answer:** *S. fuelleborni* is a parasite of non-human primates that can infect humans. In infants, heavy infection leads to a severe protein-losing enteropathy. This results in profound **hypoalbuminemia**, which causes generalized edema and massive ascites, giving the characteristic "swollen belly" appearance. It is often associated with respiratory distress and high mortality if untreated. **Analysis of Incorrect Options:** * **A. *Ascaris lumbricoides*:** While heavy Ascaris infections can cause abdominal distension due to a large bolus of worms (intestinal obstruction), it does not cause the specific clinical triad of SBS (ascites/hypoalbuminemia). * **B. *Strongyloides stercoralis*:** This is the common human threadworm. It causes "Hyperinfection Syndrome" in immunocompromised hosts but is not the specific cause of the SBS clinical entity. * **D. *Wuchereria bancrofti*:** This filarial nematode causes lymphatic filariasis. While it can cause "Chylous ascites" in rare cases, its hallmark is elephantiasis of the limbs and scrotum, not Swollen Belly Syndrome. **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** *S. fuelleborni* is unique because it can be transmitted via **breast milk** (transmammary transmission), which explains why it affects very young infants. * **Diagnosis:** Identification of eggs in the stool (unlike *S. stercoralis*, where larvae are usually found). * **Treatment:** Albendazole or Ivermectin. * **Key Association:** Always link "Swollen Belly Syndrome" + "Infant" + "Papua New Guinea" to *Strongyloides fuelleborni*.

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).

Question 1

A patient with AIDS experienced an acute episode of diarrhea. Stool examination revealed an oval structure, 8 to 9 micrometers in diameter, that was acid-fast and fluoresced blue under ultraviolet light. What is the most likely identification of this organism?

Accepted Answer

Cyclospora

Answer

Cryptosporidium

Answer

Enterocytozoon

Answer

Giardia

Question 2

What causes swollen belly syndrome?

Accepted Answer

Strongyloides fuelleborni

Answer

Ascaris lumricoides

Answer

Strongyloides stercoralis

Answer

Wucheraria bancrofti

Question 3

A 50-year-old male presented with various subcutaneous nodules over the right iliac crest, measuring approximately 1 cm in diameter. Adult worms and microfilariae were detected within the excised nodules. Which of the following organisms is likely the causative agent?

Accepted Answer

Loa Loa

Answer

Onchocerca volvulus

Answer

Mansonella

Answer

Brugia malayi

Question 4

Which of the following parasites is NOT transmitted by fish?

Accepted Answer

Schistosoma japonicum

Answer

Paragonimus westermanii

Answer

Clonorchis sinensis

Answer

Diphyllobothrium latum

Question 5

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

Accepted Answer

Strongyloides

Answer

Toxoplasma

Answer

Trichuris

Answer

Ankylostoma

Question 6

Katayama fever is caused by which of the following parasites?

Accepted Answer

Schistosoma mansoni

Answer

Fasciola hepatica

Answer

Clonorchis sinensis

Answer

Ascaris lumbricoides

Question 7

Opisthorchis sinensis can cause which of the following malignancies?

Accepted Answer

Cholangiocarcinoma

Answer

Hepatocellular carcinoma

Answer

Pancreatic carcinoma

Answer

All of the above

Question 8

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 9

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 10

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

Parasitology — MCQs

Parasitology — MCQs

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