Parasitology Practice Questions

Q: Which of the following is NOT a true statement about filariasis?

Man serves as the intermediate host.. ### Explanation In the life cycle of *Wuchereria bancrofti*, **Man is the Definitive Host**, not the intermediate host. By definition, a definitive host is one in which the parasite reaches maturity and undergoes sexual reproduction. In filariasis, adult male and female worms mate within the human lymphatic system to produce microfilariae. The **Mosquito (Culex/Aedes/Anopheles) serves as the Intermediate Host**, where the parasite undergoes essential developmental stages (L1 to L3 larvae) but does not reproduce sexually. **Analysis of Other Options:** * **Option A:** The **Extrinsic Incubation Period** (the time taken for microfilariae to develop into infective L3 larvae inside the mosquito) is typically **10–14 days**, depending on environmental temperature and humidity. * **Option C:** Adult worms primarily inhabit the **afferent lymphatic vessels** and lymph nodes, leading to the classic clinical manifestations of lymphatic filariasis like lymphedema and elephantiasis. * **Option D:** Filariasis follows a **Cyclo-developmental** pattern of transmission. This means the parasite undergoes essential developmental changes (stages) within the vector, but there is **no multiplication** (one microfilaria ingested becomes only one infective larva). **NEET-PG High-Yield Pearls:** * **Infective Stage for Man:** L3 (Third-stage) larvae. * **Diagnostic Stage:** Microfilariae (found in peripheral blood, usually with nocturnal periodicity). * **Drug of Choice:** Diethylcarbamazine (DEC) 6mg/kg for 12 days. * **Mass Drug Administration (MDA):** Uses a single annual dose of DEC + Albendazole (or IDA: Ivermectin + DEC + Albendazole in specific areas). * **Vector for *W. bancrofti* in India:** *Culex quinquefasciatus* (breeds in dirty/stagnant water).

Q: Larvae of which of the following parasites reside in muscle tissue?

Trichinella. **Explanation:** The correct answer is **Trichinella spiralis**. This parasite is unique among nematodes because it completes its entire life cycle (adults and larvae) within a single host. After ingestion of undercooked meat (usually pork) containing encysted larvae, the larvae mature into adults in the small intestine. The female then releases newborn larvae that enter the bloodstream and selectively migrate to **striated skeletal muscles** (especially active muscles like the diaphragm, tongue, and deltoid). Here, they encyst within muscle cells, transforming them into "nurse cells." **Why the other options are incorrect:** * **Ascaris lumbricoides (Roundworm):** The larvae undergo a heart-lung migration (Loeffler’s syndrome) but eventually reside as adults in the **small intestine**. They do not encyst in muscle. * **Hookworm (Ancylostoma/Necator):** Larvae penetrate the skin and migrate through the lungs to reach the **small intestine**, where they attach to the mucosa to suck blood. * **Pinworm (Enterobius vermicularis):** This parasite has no tissue migration phase. The entire life cycle occurs within the **gastrointestinal tract**, with females migrating to the perianal skin to lay eggs. **High-Yield NEET-PG Pearls:** * **Clinical Triad of Trichinellosis:** Myalgia (muscle pain), periorbital edema, and eosinophilia. * **Diagnosis:** Muscle biopsy (showing coiled larvae) or the **Bachman intradermal test**. * **Dead-end Host:** Humans are considered dead-end hosts because the larvae encysted in our muscles are unlikely to be ingested by another host. * **Drug of Choice:** Albendazole or Mebendazole.

Q: The following Peripheral Smear shows the presence of?

Gametocyte. ***Gametocyte*** - The **crescent** or **banana-shaped** structure seen in peripheral blood smear is characteristic of **Plasmodium falciparum gametocytes**. - Gametocytes are the **sexual forms** of the malaria parasite responsible for **transmission** to mosquitoes and are diagnostic of malaria infection. *Sporozoite* - Sporozoites are the **infective forms** found in mosquito salivary glands and are **not visible** in peripheral blood smears. - They rapidly migrate to the **liver** within minutes of mosquito bite and cannot be detected in routine blood examination. *Merozoite* - Merozoites are **briefly present** in blood after liver schizont rupture but appear as **ring forms** when they invade RBCs. - They do not have the characteristic **crescent shape** and are typically seen as small ring-like structures within red blood cells. *Schistocyte* - Schistocytes are **fragmented red blood cells** with irregular shapes, not parasitic forms. - They indicate **microangiopathic hemolytic anemia** and lack the organized crescent structure of malarial gametocytes.

Q: Profuse watery diarrhea in an immunocompromised child is due to which pathogen?

Cryptosporidium. **Explanation:** **Cryptosporidium hominis/parvum** is the most common cause of severe, life-threatening, profuse watery diarrhea in immunocompromised individuals, particularly those with HIV/AIDS (CD4 count <200 cells/mm³) or children with primary immunodeficiencies. The parasite infects the intestinal epithelium, causing malabsorption and electrolyte imbalance. While it causes self-limiting diarrhea in healthy individuals, it leads to chronic, cholera-like diarrhea in the immunocompromised. **Analysis of Incorrect Options:** * **Amoeba (Entamoeba histolytica):** Typically presents as **amoebic dysentery** (bloody stools with mucus) and tenesmus, rather than profuse watery diarrhea. It is characterized by flask-shaped ulcers in the colon. * **Giardia lamblia:** Causes **steatorrhea** (foul-smelling, greasy stools that float) and bloating. It is more common in children but does not typically cause the massive fluid loss seen with Cryptosporidium. * **Lactose Intolerance:** This is a non-infectious condition resulting from lactase deficiency. While it causes osmotic diarrhea, it is usually triggered by dairy intake and is not specifically associated with an immunocompromised state. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Modified Acid-Fast Staining (Kinyoun stain) reveals **bright red, spherical oocysts** (4–6 µm). * **Transmission:** Fecal-oral route; notably **chlorine-resistant**, making it a common cause of swimming pool-associated outbreaks. * **Treatment:** Nitazoxanide is the drug of choice in immunocompetent patients; however, in HIV patients, the primary treatment is **HAART** to restore immune function. * **Other Coccidian Parasites:** *Isospora belli* (larger, elliptical oocysts) and *Cyclospora* (larger, spherical oocysts) also cause similar diarrhea in AIDS patients.

Q: Which parasite causes lung cysts?

Echinococcus. **Explanation:** **Echinococcus granulosus** (the dog tapeworm) is the causative agent of **Hydatid disease**. In humans (accidental intermediate hosts), the ingested eggs hatch into oncospheres that penetrate the intestinal wall and enter the portal circulation. While the **liver** is the most common site (approx. 70%), the **lungs** are the second most common site (approx. 20-25%) for the formation of slow-growing, fluid-filled **hydatid cysts**. These cysts are characterized by a three-layered wall (pericyst, ectocyst, and endocyst) and can cause symptoms like cough, chest pain, or hemoptysis. **Analysis of Incorrect Options:** * **Ascaris lumbricoides:** While it causes pulmonary symptoms during the larval migration phase (**Loeffler’s syndrome**), it results in transient eosinophilic infiltrates, not permanent or fluid-filled cysts. * **Toxocara canis:** Causes **Visceral Larva Migrans**. It leads to granulomatous lesions in the liver, lungs, or eyes, but does not form true hydatid-like cysts. * **Trypanosoma:** *T. cruzi* (Chagas disease) primarily affects the heart (myocarditis) and GI tract (mega-esophagus/colon), while *T. brucei* causes Sleeping Sickness. Neither is associated with lung cysts. **High-Yield NEET-PG Pearls:** * **Radiology:** Look for the **"Water-lily sign"** (Casoni’s sign) or "Camelot sign" on CXR, indicating a ruptured endocyst floating in the cyst fluid. * **Diagnosis:** Indirect Hemagglutination (IHA) or ELISA; **Casoni’s intradermal test** is now largely historical. * **Treatment:** Surgical removal is preferred. **PAIR** (Puncture, Aspiration, Injection, Re-aspiration) is a minimally invasive alternative. Medical management involves **Albendazole**. * **Risk:** Rupture of a lung cyst can lead to life-threatening **anaphylactic shock**.

Q: Transovarian transmission of infection occurs in which of the following vectors?

Sandflies. **Explanation:** **Transovarian transmission** refers to the passage of a pathogen from a female vector to its offspring via the eggs. This mechanism allows the pathogen to persist in the environment even in the absence of a vertebrate host. **Why Sandflies are correct:** In the context of medical parasitology and entomology, sandflies (*Phlebotomus* species) are well-known for the transovarian transmission of **Sandfly fever virus** (Pappataci fever). While sandflies are primarily famous for transmitting *Leishmania donovani*, the vertical transmission of the virus through their eggs ensures the viral reservoir remains stable across generations. **Analysis of Incorrect Options:** * **Fleas:** Primarily transmit *Yersinia pestis* (Plague) via the "blocked flea" mechanism (regurgitation) and *Rickettsia typhi* (Endemic typhus) through feces. Transovarian transmission is not a significant feature. * **Mosquitoes:** While mosquitoes transmit numerous diseases (Malaria, Filaria, Dengue), the pathogens usually require a cycle in the vertebrate host. While some viruses (like West Nile) show low levels of vertical transmission, it is not their defining characteristic compared to the classic examples. * **Ticks:** Ticks are actually the **most classic** example of transovarian transmission (specifically for *Rickettsia rickettsii* and *Babesia*). However, given the specific options provided in this question, Sandflies are the designated correct answer for viral transmission. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Examples of Transovarian Transmission:** Ticks (Babesiosis, Rocky Mountain Spotted Fever) and Sandflies (Sandfly Fever). * **Sandfly (Phlebotomus):** Vector for Kala-azar (Leishmaniasis), Oriental sore, Sandfly fever, and Oroya fever (Bartonellosis). * **Key Vector Fact:** The sandfly is the smallest significant disease-carrying insect; it cannot fly against the wind and hops rather than flies.

Q: Which of the following is NOT associated with Loeffler's syndrome?

Giardiasis. **Explanation:** **Loeffler’s Syndrome** (Simple Pulmonary Eosinophilia) is a transient respiratory illness characterized by migratory pulmonary infiltrates and peripheral blood eosinophilia [1]. The underlying pathophysiology involves a **Type I hypersensitivity reaction** in the lungs, typically occurring during the larval migration phase of certain helminths. **Why Giardiasis is the correct answer:** * **Giardiasis** is caused by *Giardia lamblia*, a protozoan that inhabits the duodenum and upper jejunum [3]. Unlike helminths, *Giardia* does **not** have a tissue-migratory phase through the lungs; it remains localized to the gastrointestinal tract [3]. Therefore, it does not cause pulmonary eosinophilia or Loeffler’s syndrome. **Analysis of incorrect options:** * **Toxocara & Strongyloides stercoralis:** These are classic causes of Loeffler’s syndrome [1]. Along with *Ascaris lumbricoides* and Ancylostoma (Hookworms), these parasites undergo a **heart-lung migration cycle** [2]. As larvae break into the alveoli, they trigger an eosinophilic immune response. * **L-tryptophan:** While primarily associated with **Eosinophilia-Myalgia Syndrome (EMS)**, historical contamination of L-tryptophan supplements has been linked to systemic eosinophilic syndromes that can present with Loeffler-like pulmonary infiltrates. **NEET-PG High-Yield Pearls:** * **Most common cause:** *Ascaris lumbricoides* is the most frequent global cause of Loeffler’s syndrome. * **Clinical Presentation:** Usually self-limiting; presents with dry cough, wheezing, and dyspnea [4]. * **Radiology:** Characterized by **"fleeting" or "migratory" pulmonary infiltrates** (shadows that change position on serial X-rays) [1]. * **Mnemonic (NASSA):** Common parasites causing Loeffler’s: **N**ecator americanus, **A**scaris lumbricoides, **S**trongyloides stercoralis, **S**chistosoma, **A**ncylostoma duodenale [1], [2].

Q: What is the causative agent of River blindness?

Onchocerca volvulus. **Explanation:** **Onchocerca volvulus** is the correct answer as it is the causative agent of **Onchocerciasis**, commonly known as **River Blindness**. The disease is transmitted through the bite of the **Simulium fly (Blackfly)**, which breeds in fast-flowing rivers. The pathology is primarily caused by the host's inflammatory response to dying microfilariae in the skin and eyes, leading to sclerosing keratitis and eventual blindness. **Analysis of Incorrect Options:** * **Loa loa:** Also known as the "African eye worm," it causes **Calabar swellings** (fugitive swellings). While the adult worm can be seen migrating across the subconjunctiva of the eye, it typically does not cause blindness. It is transmitted by the *Chrysops* fly (Deer fly). * **Wuchereria bancrofti:** This is the primary agent of **Lymphatic Filariasis**. It targets the lymphatic system, leading to lymphedema and elephantiasis (usually of the lower limbs and scrotum). It is transmitted by the *Culex* mosquito and does not involve ocular pathology. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Simulium* fly (Blackfly). * **Clinical Triad:** Dermatitis (intense itching/Lizard skin), Subcutaneous nodules (Onchocercomas), and Ocular lesions (River blindness). * **Diagnosis:** **Skin snip test** is the gold standard (to demonstrate microfilariae). Note: Microfilariae are NOT found in the blood (non-sheathed). * **Treatment:** **Ivermectin** is the drug of choice (DOC). It kills microfilariae but not adult worms. * **Mazzotti Reaction:** A severe systemic reaction (fever, rash, hypotension) that can occur after treating Onchocerciasis with Diethylcarbamazine (DEC) due to the rapid killing of microfilariae.

Question 1

Which of the following is NOT a true statement about filariasis?

Accepted Answer

Man serves as the intermediate host.

Answer

The extrinsic incubation period is 10-14 days.

Answer

Adult worms reside in the lymphatics of the host.

Answer

There is no multiplication of the parasite within the mosquito vector.

Question 2

An anxious mother brought her 4-year-old daughter to the pediatrician. The girl was passing loose stools for the past 20 days, often associated with abdominal pain. Stool examination showed the following organism:

Accepted Answer

Giardia lamblia

Answer

Cryptosporidium parvum

Answer

E. coli

Answer

Entamoeba histolytica

Question 3

Larvae of which of the following parasites reside in muscle tissue?

Accepted Answer

Trichinella

Answer

Ascaris

Answer

Hookworm

Answer

Pinworm

Question 4

The following Peripheral Smear shows the presence of?

Accepted Answer

Gametocyte

Answer

Sporozoite

Answer

Merozoite

Answer

Schistocyte

Question 5

Profuse watery diarrhea in an immunocompromised child is due to which pathogen?

Accepted Answer

Cryptosporidium

Answer

Amoeba

Answer

Giardia

Answer

Lactose intolerance

Question 6

All of the following are true about amebic liver abscess except?

Accepted Answer

Trophozoites in stool are essential for clinical diagnosis

Answer

Mostly asymptomatic

Answer

More common in males than females

Answer

Rarely affects brain, eye, and skin

Question 7

Which parasite causes lung cysts?

Accepted Answer

Echinococcus

Answer

Ascaris

Answer

Toxocara

Answer

Trypanosoma

Question 8

Transovarian transmission of infection occurs in which of the following vectors?

Accepted Answer

Sandflies

Answer

Fleas

Answer

Ticks

Answer

Mosquitoes

Question 9

Which of the following is NOT associated with Loeffler's syndrome?

Accepted Answer

Giardiasis

Answer

Toxocara

Answer

Strongyloides stercoralis

Answer

L. tryptophan

Question 10

What is the causative agent of River blindness?

Accepted Answer

Onchocerca volvulus

Answer

Loa loa

Answer

Wuchereria bancrofti

Answer

All of the above

Parasitology — MCQs

Parasitology — MCQs

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