Parasitology Practice Questions

Q: Ova in stool are not of diagnostic significance in which of the following helminthic infections?

Strongyloides. ### Explanation The diagnostic hallmark of **Strongyloides stercoralis** (Threadworm) infection is the presence of **rhabditiform larvae** in the stool, not eggs (ova). **Why Strongyloides is the correct answer:** In the life cycle of *Strongyloides stercoralis*, the adult female lives in the submucosa of the small intestine and lays eggs. These eggs hatch almost immediately within the intestinal mucosa. Therefore, by the time the parasite is excreted in the feces, it is already in the **larval stage**. Finding eggs in the stool is extremely rare and usually only occurs in cases of severe hyperinfection or heavy purgation. **Analysis of Incorrect Options:** * **Ankylostoma duodenale (Hookworm):** Diagnosis is primarily made by identifying characteristic **non-bile stained, segmented eggs** (usually at the 4-8 cell stage) in the stool. * **Enterobius vermicularis (Pinworm):** While the NIH swab/Scotch tape test is the gold standard (detecting eggs on the perianal skin), the diagnostic stage is the **planoconvex egg**. These are occasionally seen in routine stool exams, though less frequently than other helminths. * **Trichuris trichiura (Whipworm):** Diagnosis is confirmed by finding the characteristic **barrel-shaped eggs** with bipolar mucus plugs in the stool. **High-Yield Clinical Pearls for NEET-PG:** * **Strongyloides** is unique because it can cause **autoinfection**, where rhabditiform larvae transform into filariform larvae within the gut and re-penetrate the intestinal wall or perianal skin. * **Hyperinfection syndrome** is a life-threatening complication seen in immunocompromised patients (especially those on steroids). * **Larva Currens:** A rapidly moving, serpiginous cutaneous eruption is pathognomonic for Strongyloides. * **Drug of Choice:** Ivermectin is the preferred treatment for Strongyloidiasis.

Q: A 30-year-old female stored her contact lenses in tap water and presented with severe retinitis and deterioration of vision. Culture of the tap water and vitreous fluid would most likely reveal which of the following microorganisms?

Acanthamoeba. **Explanation:** The clinical presentation of a contact lens wearer using tap water for storage who develops severe ocular involvement is a classic "high-yield" scenario for **Acanthamoeba keratitis**. **Why Acanthamoeba is correct:** Acanthamoeba is a free-living amoeba found in soil and water (including tap water). In contact lens users, poor hygiene—specifically using non-sterile tap water or homemade saline—allows the organism to contaminate the lenses. It causes a painful, sight-threatening keratitis characterized by a pathognomonic **ring-shaped corneal infiltrate**. Diagnosis is confirmed by demonstrating trophozoites or double-walled cysts on corneal scrapings or culture on **non-nutrient agar (NNA) seeded with E. coli**. **Why other options are incorrect:** * **Naegleria fowleri:** Known as the "brain-eating amoeba," it causes Primary Amoebic Meningoencephalitis (PAM) after swimming in warm freshwater. It does not typically cause ocular infections. * **Pneumocystis jirovecii:** An opportunistic fungus that primarily causes interstitial pneumonia in immunocompromised patients (e.g., HIV/AIDS). It is not associated with contact lens use or keratitis. * **Babesia:** An intraerythrocytic protozoan transmitted by *Ixodes* ticks, causing a malaria-like illness (Babesiosis). It does not cause eye infections. **Clinical Pearls for NEET-PG:** * **Stain of choice:** Calcofluor white (binds to chitin in the cyst wall). * **Culture medium:** Non-nutrient agar with *E. coli* (look for "trailing" or "tracks" made by the amoeba). * **Pathognomonic sign:** Radial keratoneuritis (inflammation of corneal nerves) leading to exquisite pain out of proportion to clinical findings. * **Treatment:** Topical biguanides (PHMB) or chlorhexidine.

Q: Plasmodium falciparum infection of man is characterized by?

Multiple infections of erythrocytes are seen.. ### Explanation **Correct Answer: C. Multiple infections of erythrocytes are seen.** *Plasmodium falciparum* is unique among malaria species due to its high parasitemia and specific morphological features in peripheral blood. **Why Option C is Correct:** *P. falciparum* can infect up to 30-40% of circulating RBCs. A hallmark diagnostic feature is **multiple infections of a single erythrocyte**, where two or more "ring forms" (trophozoites) are seen within one red cell. This occurs because *P. falciparum* can invade RBCs of all ages (young reticulocytes to old cells), unlike other species. **Why Other Options are Incorrect:** * **Option A:** Erythrocytes remain **normal in size**. Enlarged RBCs are characteristic of *P. vivax* and *P. ovale*, which preferentially infect young, flexible reticulocytes. * **Option B:** In *P. falciparum*, only **ring forms and gametocytes** are typically seen in peripheral blood. Mature schizonts and trophozoites undergo **sequestration** in deep capillaries (brain, kidneys, placenta) due to "knobs" on the RBC surface (PfEMP-1 protein), leading to cytoadherence. Seeing schizonts in a peripheral smear indicates "grave prognosis." * **Option D:** The erythrocytic cycle of *P. falciparum* lasts **48 hours**, resulting in **Malignant Tertian Malaria**. A 72-hour cycle is characteristic of *P. malariae* (Quartan Malaria). **High-Yield Clinical Pearls for NEET-PG:** * **Maurer’s Clefts:** Coarse granulations seen in *P. falciparum* infected RBCs. * **Accole/Applique forms:** Ring forms appearing at the very periphery of the RBC. * **Gametocytes:** Characteristically **crescent or banana-shaped**. * **Complications:** Cerebral malaria, Blackwater fever (hemoglobinuria), and ARDS are most common with *falciparum*.

Q: Which among the following parasites is associated with malignancy?

Schistosoma hematobium. ### Explanation **Correct Option: B. Schistosoma hematobium** *Schistosoma hematobium* (the urinary blood fluke) is a well-established Group 1 carcinogen. The parasite resides in the vesical venous plexus. Chronic infection leads to the deposition of eggs in the bladder wall, causing chronic inflammation and irritation. Over time, this results in squamous metaplasia of the transitional epithelium, ultimately leading to **Squamous Cell Carcinoma (SCC) of the urinary bladder**. * *Key Distinction:* While most bladder cancers worldwide are Transitional Cell Carcinomas (TCC), Schistosomiasis specifically predisposes to the **Squamous Cell** variety. **Analysis of Incorrect Options:** * **A. Echinococcus granulosus:** Causes Hydatid cyst disease (primarily in the liver and lungs). While it causes space-occupying lesions and potential anaphylaxis upon rupture, it is not associated with malignancy. * **C. Paragonimus westermani:** The lung fluke causes a condition mimicking tuberculosis (hemoptysis and cavitary lesions) but is not oncogenic. * **D. Giardia lamblia:** An intestinal protozoan causing malabsorption and steatorrhea; it does not lead to neoplastic changes. **NEET-PG High-Yield Pearls:** 1. **Other Parasites & Malignancy:** * *Clonorchis sinensis* (Chinese liver fluke) and *Opisthorchis viverrini* are strongly associated with **Cholangiocarcinoma** (bile duct cancer). 2. **Diagnostic Feature:** *S. hematobium* eggs are characterized by a **terminal spine**. 3. **Intermediate Host:** Freshwater snails of the genus *Bulinus*. 4. **Drug of Choice:** Praziquantel is the gold standard treatment for all Schistosoma species.

Q: Which organism is associated with the causation of urinary bladder cancer?

Schistosoma. **Explanation:** The correct answer is **Schistosoma haematobium**. This parasite is a well-known risk factor for **Squamous Cell Carcinoma (SCC)** of the urinary bladder. **1. Why Schistosoma is correct:** *Schistosoma haematobium* (the urinary blood fluke) resides in the vesical and pelvic venous plexuses. The female fluke deposits eggs in the bladder wall, which possess a characteristic **terminal spine**. These eggs cause chronic irritation, granuloma formation, and persistent inflammation. Over years, this chronic inflammatory state leads to **squamous metaplasia** of the bladder urothelium, which eventually progresses to Squamous Cell Carcinoma (unlike the more common transitional cell carcinoma seen in smokers). **2. Why other options are incorrect:** * **E. coli:** While the most common cause of urinary tract infections (UTIs), it is not an oncogenic organism. * **Paragonimus westermani:** Known as the lung fluke, it primarily causes pulmonary symptoms (hemoptysis) mimicking tuberculosis. * **Clonorchis sinensis:** Known as the Chinese liver fluke, it inhabits the bile ducts and is strongly associated with **Cholangiocarcinoma** (bile duct cancer), not bladder cancer. **3. High-Yield Clinical Pearls for NEET-PG:** * **Intermediate Host:** Freshwater snail (*Bulinus* species). * **Infective Stage:** Cercaria (enters via skin penetration during swimming). * **Diagnostic Feature:** Eggs with a **terminal spine** in urine microscopy. * **Drug of Choice:** Praziquantel. * **Key Distinction:** Most bladder cancers worldwide are Transitional Cell Carcinomas (TCC), but in endemic areas of Schistosomiasis (e.g., Egypt/Nile Valley), SCC is more prevalent.

Q: Which parasitic intestinal infestation is commonly seen in immunosuppressed patients?

Strongyloides. **Explanation:** The correct answer is **Strongyloides stercoralis**. The underlying medical concept is the unique ability of this parasite to undergo **autoinfection**. 1. **Why Strongyloides is correct:** Unlike most helminths, *Strongyloides stercoralis* can complete its entire life cycle within the human host. Rhabditiform larvae in the intestine can transform into infective filariform larvae, which penetrate the perianal skin or intestinal mucosa to re-enter the circulation. In **immunosuppressed patients** (especially those on high-dose corticosteroids, HTLV-1 infection, or hematologic malignancies), this process accelerates uncontrollably, leading to **Hyperinfection Syndrome** and **Disseminated Strongyloidiasis**. This can result in life-threatening complications like Gram-negative sepsis due to the translocation of enteric bacteria. 2. **Why other options are incorrect:** * **Giardiasis:** While common, it is not specifically associated with severe systemic dissemination in immunosuppression, though it may be more persistent in IgA deficiency. * **Ascariasis:** *Ascaris lumbricoides* requires a period in the soil to become infective; it cannot replicate or cause hyperinfection within the host. * **Liver fluke:** (e.g., *Clonorchis sinensis*) These infections are related to the ingestion of contaminated fish and are not primarily driven by the host's immune status. **High-Yield NEET-PG Pearls:** * **Drug of Choice:** Ivermectin (preferred over Albendazole). * **Diagnostic Clue:** Presence of **rhabditiform larvae** in stool (eggs are rarely seen as they hatch in the mucosa). * **Steroid Warning:** Always screen for *Strongyloides* before initiating long-term corticosteroids in endemic areas to prevent fatal hyperinfection. * **Larva Currens:** A pathognomonic, rapidly moving serpiginous cutaneous eruption.

Q: Which cycle is observed in RBCs during malaria?

Endogenous cycle. **Explanation:** The life cycle of the *Plasmodium* parasite is divided into two distinct phases based on the host: the **Endogenous cycle** (in humans) and the **Exogenous cycle** (in the female Anopheles mosquito). 1. **Why the Correct Answer is Right:** The **Endogenous cycle** occurs entirely within the human host. It consists of two main stages: * **Pre-erythrocytic (Exo-erythrocytic) Schizogony:** Occurs in the liver cells (hepatocytes). * **Erythrocytic Schizogony:** Occurs within the **Red Blood Cells (RBCs)**. Since the multiplication within RBCs happens inside the human body, it is a component of the endogenous cycle. 2. **Why the Other Options are Wrong:** * **Sexual Cycle:** This occurs in the mosquito (the definitive host). It begins with gametogony (initiated in humans but completed in mosquitoes) and ends with the formation of a zygote and ookinete. * **Sporogony:** This is the phase of asexual multiplication that occurs in the **mosquito**. It leads to the production of infective sporozoites. * **Exogenous Cycle:** This refers to the development of the parasite outside the human body (within the mosquito). It encompasses both the sexual cycle and sporogony. **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Female Anopheles mosquito (where the sexual cycle occurs). * **Intermediate Host:** Humans (where the asexual/endogenous cycle occurs). * **Infective Form to Humans:** Sporozoites (injected via mosquito bite). * **Infective Form to Mosquito:** Gametocytes (ingested during a blood meal). * **Relapse vs. Recrudescence:** Relapse is caused by **hypnozoites** (latent liver forms) in *P. vivax* and *P. ovale*. Recrudescence is due to the persistence of blood forms in *P. falciparum*. * **Schüffner’s dots:** Characteristically seen in RBCs infected with *P. vivax* and *P. ovale*.

Q: Auto-infection is characteristic of which of the following helminths?

Enterobius vermicularis. ### Explanation **Correct Answer: D. Enterobius vermicularis** **Mechanism of Auto-infection:** Auto-infection occurs when an individual serves as both the source and the host for a new cycle of infection without the parasite needing to undergo a developmental stage in the external environment. In **Enterobius vermicularis** (Pinworm), the female migrates to the perianal skin at night to lay eggs. These eggs become infective within 4–6 hours. Intense itching (pruritus ani) leads to scratching, and the eggs are transferred to the mouth via contaminated fingers (**fecal-oral route**). Additionally, **retro-infection** can occur when larvae hatch on the perianal skin and migrate back into the colon. **Why the other options are incorrect:** * **A. Trichuris trichura (Whipworm):** Eggs are passed unembryonated in feces and require approximately 2–4 weeks in warm, moist soil to become infective. Direct person-to-person transmission is impossible. * **B. Ankylostoma duodenale (Hookworm):** Eggs hatch into rhabditiform larvae in the soil, which then transform into infective filariform larvae. Infection occurs via skin penetration, not direct ingestion of eggs from the host. * **C. Ascaris lumbricoides (Roundworm):** Eggs must undergo embryonation in the soil (taking 2–3 weeks) before they become infective. Freshly passed eggs are not infectious. **NEET-PG High-Yield Pearls:** * **List of Helminths showing Auto-infection:** *Enterobius vermicularis*, *Strongyloides stercoralis* (internal auto-infection), *Hymenolepis nana*, and *Taenia solium*. * **Diagnostic Gold Standard:** NIH Swab or Scotch Tape (Cellophane tape) test, performed early in the morning before bathing. * **Drug of Choice:** Albendazole or Mebendazole (treat the entire family to prevent reinfection). * **Clinical Sign:** Perianal pruritus and nocturnal enuresis in children.

Question 1

Ova in stool are not of diagnostic significance in which of the following helminthic infections?

Accepted Answer

Strongyloides

Answer

Ankylostoma

Answer

Enterobius

Answer

Trichuris

Question 2

A 30-year-old female stored her contact lenses in tap water and presented with severe retinitis and deterioration of vision. Culture of the tap water and vitreous fluid would most likely reveal which of the following microorganisms?

Accepted Answer

Acanthamoeba

Answer

Naegleria

Answer

Pneumocystis

Answer

Babesia

Question 3

Plasmodium falciparum infection of man is characterized by?

Accepted Answer

Multiple infections of erythrocytes are seen.

Answer

Erythrocytes are increased in size.

Answer

All stages of erythrocytic schizogony are seen in peripheral blood.

Answer

Each erythrocytic cycle lasts 72 hours.

Question 4

Which among the following parasites is associated with malignancy?

Accepted Answer

Schistosoma hematobium

Answer

Echinococcus granulosus

Answer

Paragonimus westermani

Answer

Giardia lamblia

Question 5

Which organism is associated with the causation of urinary bladder cancer?

Accepted Answer

Schistosoma

Answer

E. coli

Answer

Paragonimus

Answer

Clonorchis

Question 6

Which parasitic intestinal infestation is commonly seen in immunosuppressed patients?

Accepted Answer

Strongyloides

Answer

Giardiasis

Answer

Ascariasis

Answer

Liver fluke

Question 7

Which cycle is observed in RBCs during malaria?

Accepted Answer

Endogenous cycle

Answer

Sexual cycle

Answer

Sporogony

Answer

Exogenous cycle

Question 8

Which of the following statements is true regarding microsporidia?

Accepted Answer

It is associated with diarrhea in HIV patients.

Answer

It is a fungus.

Answer

It is a protozoan.

Answer

It is a bacterium.

Question 9

Which of the following are neuropathogenic amoeba?

Accepted Answer

Entamoeba coli

Answer

Acanthamoeba

Answer

Naegleria

Answer

Entamoeba Histolytica

Question 10

Auto-infection is characteristic of which of the following helminths?

Accepted Answer

Enterobius vermicularis

Answer

Trichuris trichura

Answer

Ankylostoma duodenale

Answer

Ascaris lumbricoides

Parasitology — MCQs

Parasitology — MCQs

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