Parasitology Practice Questions

Q: Which of the following diseases is not transmitted by Aedes mosquitoes?

Bancroftian filariasis. **Explanation:** The correct answer is **Bancroftian filariasis** because its primary vector is the **Culex mosquito** (specifically *Culex quinquefasciatus*), not the *Aedes* mosquito. While *Aedes* species can transmit certain types of filariasis (like *Brugia malayi* in specific regions), the classic Bancroftian filariasis caused by *Wuchereria bancrofti* is globally associated with *Culex* in urban and semi-urban settings. **Analysis of Options:** * **Yellow fever:** This is a viral hemorrhagic fever caused by a Flavivirus. It is primarily transmitted by *Aedes aegypti* (urban cycle) and *Haemagogus* species (sylvatic cycle). * **Dengue fever:** Caused by the Dengue virus (Flavivirus), it is the most common mosquito-borne viral disease in humans, transmitted predominantly by *Aedes aegypti* and *Aedes albopictus*. * **Chikungunya fever:** Caused by an Alphavirus (Togaviridae), it is transmitted to humans by the same *Aedes* vectors (*A. aegypti* and *A. albopictus*), often leading to outbreaks in the same geographical areas as Dengue. **High-Yield Clinical Pearls for NEET-PG:** * **Aedes Characteristics:** Known as "Day biters" (peak activity at dawn and dusk) and "Tiger mosquitoes" due to white stripes on their legs. They breed in artificial collections of clean water (e.g., flower pots, discarded tires). * **Vector Mnemonics:** * **Culex:** Bancroftian Filariasis, Japanese Encephalitis, West Nile Virus. * **Anopheles:** Malaria. * **Aedes:** Dengue, Chikungunya, Yellow Fever, Zika Virus. * **Wuchereria bancrofti:** Exhibits **nocturnal periodicity** (microfilariae appear in peripheral blood between 10 PM and 2 AM), correlating with the biting habits of the *Culex* mosquito.

Q: Which of the following parasites does not affect the eyes?

Trichuris. **Explanation:** The correct answer is **Trichuris trichiura** (Whipworm). This parasite primarily inhabits the large intestine (caecum) of humans. It causes Trichuriasis, which is clinically characterized by abdominal pain, bloody diarrhea, and, in severe cases, rectal prolapse. It has no life cycle stage or migratory pattern that involves the ocular tissues. **Analysis of Incorrect Options:** * **Onchocerca volvulus:** Known for causing **"River Blindness."** The microfilariae migrate to the ocular tissues, leading to sclerosing keratitis and chorioretinitis, making it a leading cause of infectious blindness. * **Trypanosoma:** Specifically, *Trypanosoma cruzi* (Chagas disease) often presents with **Romaña’s sign**—painless, unilateral periorbital edema and conjunctivitis—resulting from the parasite entering through the conjunctiva. * **Loa loa:** Also known as the **"African Eye Worm."** The adult worms characteristically migrate through the subconjunctival tissues of the eye, causing visible movement and irritation (Calabar swellings are also associated). **NEET-PG High-Yield Pearls:** 1. **Ocular Larva Migrans:** Most commonly caused by *Toxocara canis*. 2. **Cysticercosis:** *Taenia solium* larvae can lodge in the vitreous or subretinal space. 3. **Trichinella spiralis:** Often presents with characteristic **periorbital edema** and myositis. 4. **Trichuris trichiura Key Feature:** Look for "Bipolar plugged" or "Barrel-shaped" eggs in stool microscopy.

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.

Q: The Sabin-Feldman dye test is used for the diagnosis of which of the following?

Toxoplasma. **Explanation:** The **Sabin-Feldman Dye Test** is the gold standard serological test for the diagnosis of **Toxoplasma gondii**. It is a neutralization test based on the principle that live *Toxoplasma* tachyzoites, when incubated with specific antibodies (present in the patient's serum) and a complement-like "accessory factor," lose their ability to take up alkaline methylene blue dye. * **Positive Result:** Tachyzoites remain **unstained** (colorless) because their cell membranes are lysed by the antibody-complement complex. * **Negative Result:** Tachyzoites appear **blue** as they take up the dye in the absence of specific antibodies. **Analysis of Incorrect Options:** * **A. Filaria:** Diagnosis is primarily made by demonstrating microfilariae in peripheral blood (night samples) or using the ICT antigen test (for *W. bancrofti*). * **C. Histoplasma:** This is a dimorphic fungus. Diagnosis relies on fungal culture, histopathology (Gomori Methenamine Silver stain), or urinary antigen detection. * **D. Ascaris:** Diagnosis is typically made by identifying characteristic eggs (bile-stained) in a stool examination. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard:** While the Sabin-Feldman test is the reference standard, it is rarely used in routine labs because it requires maintaining live, infectious tachyzoite cultures. * **Congenital Toxoplasmosis:** Characterized by the classic triad: **Chorioretinitis, Hydrocephalus, and Intracranial calcifications.** * **Toxoplasma in HIV:** Most common cause of space-occupying lesions (CNS lymphoma is the differential); presents as "ring-enhancing lesions" on CT/MRI. * **Drug of Choice:** Pyrimethamine + Sulfadiazine.

Q: Which organism causes lymphatic filariasis?

Wuchereria bancrofti. ### Explanation **1. Why Wuchereria bancrofti is the correct answer:** Lymphatic Filariasis (LF) is caused by filarial nematodes that inhabit the lymphatic system. **Wuchereria bancrofti** is the most significant pathogen, responsible for approximately **90% of all cases worldwide**. It primarily affects the lower limbs and genitalia, leading to classic clinical manifestations like hydrocele and elephantiasis. **2. Analysis of Incorrect Options:** * **Brugia malayi & Brugia timori:** While these organisms *also* cause lymphatic filariasis, they are responsible for the remaining 10% of cases. In the context of a single-choice question where "Wuchereria bancrofti" is an option, it is the "most correct" answer due to its global prevalence. Note: *Brugia* species typically spare the genitalia. * **Schistosoma:** This is a blood fluke (trematode) that causes Schistosomiasis (Bilharzia). It affects the venous plexuses of the bladder or intestines, not the lymphatic system. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Vector:** The most common vector for *W. bancrofti* is the **Culex quinquefasciatus** mosquito (urban areas). *Brugia* is often transmitted by *Mansonia* mosquitoes. * **Diagnosis:** The gold standard is the demonstration of **microfilariae** in a peripheral blood smear. Due to **nocturnal periodicity**, blood collection must occur between **10 PM and 2 AM**. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough, wheezing, and high eosinophil counts. * **Drug of Choice:** **Diethylcarbamazine (DEC)** is the mainstay of treatment. However, it is contraindicated in patients with heavy *Onchocerca* or *Loa loa* co-infections due to the risk of severe reactions (Mazzotti reaction).

Q: Which enzyme is utilized by the rapid diagnostic test for P. falciparum?

LDH. ### Explanation The Rapid Diagnostic Test (RDT) for Malaria is an immunochromatographic assay that detects specific plasmodial antigens in the blood. **Why LDH is the correct answer:** **Parasite Lactate Dehydrogenase (pLDH)** is a functional enzyme produced only by **living** malaria parasites. It is part of the parasite's glycolytic pathway. RDTs using monoclonal antibodies against pLDH can detect all four major human malaria species (*P. falciparum, P. vivax, P. ovale,* and *P. malariae*). Because pLDH is cleared from the blood shortly after the parasite dies, it is an excellent marker for monitoring **treatment efficacy** and identifying active infection. **Analysis of Incorrect Options:** * **HRP-2 (Histidine-Rich Protein 2):** While this is the most common antigen used to detect *P. falciparum*, it is a **protein**, not an enzyme. Furthermore, HRP-2 can persist in the bloodstream for weeks after successful treatment, leading to false positives. * **SGOT (Serum Glutamic Oxaloacetic Transaminase):** Also known as AST, this is a human liver enzyme. It may be elevated in malaria due to liver involvement or hemolysis, but it is not a diagnostic marker used in RDTs. * **Peroxidase:** This enzyme is used in various laboratory assays (like ELISA) as a signaling molecule, but it is not a specific parasite-derived antigen used for malaria diagnosis. **Clinical Pearls for NEET-PG:** * **HRP-2:** Specific for *P. falciparum* only. * **pLDH:** Can be "Pan-specific" (all species) or "Species-specific" (e.g., *P.f.* or *P.v.*). * **Prozone Effect:** High parasitemia can sometimes cause a false-negative RDT result. * **Gold Standard:** Microscopic examination of peripheral blood smears (Thick for detection, Thin for species identification) remains the gold standard.

Question 1

Which of the following diseases is not transmitted by Aedes mosquitoes?

Accepted Answer

Bancroftian filariasis

Answer

Yellow fever

Answer

Dengue fever

Answer

Chikungunya fever

Question 2

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 3

Which of the following are neuropathogenic amoeba?

Accepted Answer

Entamoeba coli

Answer

Acanthamoeba

Answer

Naegleria

Answer

Entamoeba Histolytica

Question 4

Which Plasmodium species causes enlarged Red Blood Cells (RBCs)?

Accepted Answer

P. malariae

Answer

P. vivax

Answer

P. ovale

Answer

P. falciparum

Question 5

Which of the following parasites does not affect the eyes?

Accepted Answer

Trichuris

Answer

Onchocerca volvulus

Answer

Trypanosoma

Answer

Loa loa

Question 6

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

Accepted Answer

Enterobius vermicularis

Answer

Trichuris trichura

Answer

Ankylostoma duodenale

Answer

Ascaris lumbricoides

Question 7

The Sabin-Feldman dye test is used for the diagnosis of which of the following?

Accepted Answer

Toxoplasma

Answer

Filaria

Answer

Histoplasma

Answer

Ascaris

Question 8

Which organism causes lymphatic filariasis?

Accepted Answer

Wuchereria bancrofti

Answer

Brugia malayi

Answer

Schistosoma

Answer

Brugia timori

Question 9

Which enzyme is utilized by the rapid diagnostic test for P. falciparum?

Accepted Answer

LDH

Answer

HRP-2

Answer

SGOT

Answer

Peroxidase

Question 10

All of the following are true about Brugia malayi except?

Accepted Answer

The tail tip is free from nuclei.

Answer

The intermediate hosts in India are Mansonia.

Answer

Nuclei are blurred, making counting difficult.

Answer

Adult worms are found in the lymphatic system.

Parasitology — MCQs

Parasitology — MCQs

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