Parasitology Practice Questions

Q: Which of the following is true regarding Wucheria bancrofti?

Tail tip free from nuclei. **Explanation:** *Wuchereria bancrofti* is the primary causative agent of Lymphatic Filariasis. Identifying its microfilariae in peripheral blood smears is a high-yield topic for NEET-PG, focusing on specific morphological features. **1. Why the Correct Answer is Right:** The microfilaria of *W. bancrofti* is characterized by a body filled with central granules (nuclei). A key diagnostic feature is that these **nuclei do not extend to the tip of the tail** (the tail tip is "free from nuclei"). This distinguishes it from other filarial worms like *Loa loa* (nuclei extend to the tip) or *Brugia malayi* (two terminal nuclei). **2. Why the Other Options are Wrong:** * **Option A (Unsheathed):** *W. bancrofti* microfilariae are **sheathed**. The sheath is a delicate, translucent covering (derived from the egg membrane) that is much longer than the embryo itself. Unsheathed microfilariae are characteristic of *Onchocerca volvulus* and *Mansonella* species. * **Option C (Non-periodic):** In India and most endemic regions, *W. bancrofti* exhibits **Nocturnal Periodicity**. This means microfilariae appear in the peripheral blood primarily between 10 PM and 2 AM, coinciding with the biting habits of the *Culex* mosquito vector. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Primarily *Culex quinquefasciatus* (breeds in dirty/stagnant water). * **Habitat:** Adult worms reside in the **lymphatic vessels** and nodes. * **Diagnosis:** The **Membrane Filtration Concentration (MFC)** technique is the most sensitive for detecting microfilariae. * **Drug of Choice:** **Diethylcarbamazine (DEC)**; however, in mass drug administration (MDA), it is often combined with Albendazole. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough, wheezing, and high eosinophil counts.

Q: Man is the intermediate host for which of the following infections?

Malaria. In parasitology, the classification of hosts is determined by the stage of the parasite's life cycle: * **Definitive Host:** Where the **sexual cycle** occurs or the adult parasite resides. * **Intermediate Host:** Where the **asexual cycle** occurs or the larval stages develop. ### Why Malaria is Correct In **Malaria (*Plasmodium* species)**, the sexual cycle (sporogony) takes place within the female *Anopheles* mosquito, making it the definitive host. The asexual cycle (schizogony) occurs in humans (within hepatocytes and erythrocytes). Therefore, **man is the intermediate host** for Malaria. ### Why Other Options are Incorrect * **Filaria (*Wuchereria bancrofti*):** Man is the **definitive host** because the adult worms reside in the human lymphatic system and reproduce sexually. The mosquito acts as the intermediate host (larval development). * **Dengue:** This is a viral infection. The terms "intermediate" and "definitive" host are specific to parasites. In virology, humans and mosquitoes are referred to as **reservoirs/hosts** and **vectors**, respectively. * **Plague (*Yersinia pestis*):** This is a bacterial infection. Like Dengue, the parasite host classification does not apply. Rats are the primary reservoirs, and fleas are the vectors. ### NEET-PG High-Yield Pearls * **Exceptions to the Rule:** In most parasitic infections, man is the definitive host. The major exceptions where **man is the intermediate host** are: 1. **Malaria** (*Plasmodium*) 2. **Hydatid Disease** (*Echinococcus granulosus*) 3. **Cysticercosis** (*Taenia solium* - Note: Man is the definitive host for Taeniasis, but intermediate for Cysticercosis). 4. **Toxoplasmosis** (*Toxoplasma gondii*) * **Accidental Host:** Man is an accidental (dead-end) host in Hydatid disease and Toxoplasmosis.

Q: Regarding cutaneous amoebiasis, which statement is not true?

The infection reaches the skin through the bloodstream.. ### Explanation **Cutaneous amoebiasis** is a rare but severe manifestation of *Entamoeba histolytica* infection. Understanding its pathogenesis is key to identifying the incorrect statement. **1. Why Option D is the Correct Answer (The False Statement):** The primary mode of infection in cutaneous amoebiasis is **direct inoculation** or **contiguous spread** from an internal organ to the skin, rather than hematogenous (bloodstream) spread. It typically occurs when trophozoites from an intestinal or hepatic lesion directly infect the skin through a fistulous tract or via fecal contamination of pre-existing wounds. **2. Analysis of Other Options:** * **Option A:** It is characterized by a **spreading necrotizing inflammation**. The trophozoites release proteolytic enzymes (histolysins) that cause rapid tissue destruction, leading to painful ulcers with undermined edges and a sloughing base. * **Option B:** Despite its aggressive appearance, it shows a **rapid clinical response** to anti-amoebic drugs like Metronidazole or Tinidazole. This dramatic improvement is a diagnostic hallmark. * **Option C:** The **perianal region** is the most common site. This occurs due to the direct spread of trophozoites from the rectum in patients with amoebic dysentery, especially in those with poor hygiene or following anal intercourse. **Clinical Pearls for NEET-PG:** * **Pathognomonic Feature:** Ulcers with "undermined edges" and a foul-smelling discharge. * **Diagnosis:** Demonstration of motile trophozoites (with ingested RBCs) in a wet mount of the scrapings from the ulcer base or biopsy. * **Common Sites:** Perianal area (most common), abdominal wall (post-drainage of liver abscess), and genitalia. * **Differential Diagnosis:** Must be differentiated from Squamous Cell Carcinoma and Pyoderma Gangrenosum.

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

Toxoplasmosis. **Explanation:** The **Sabin-Feldman Dye Test (SFDT)** is the gold standard serological test for the diagnosis of **Toxoplasmosis**, caused by the protozoan *Toxoplasma gondii*. **Mechanism:** The test is based on the principle of **complement-mediated neutralization**. Live tachyzoites of *T. gondii* are incubated with the patient's serum and fresh complement. * **Positive Result:** If specific antibodies are present in the patient's serum, they bind to the tachyzoites and activate the complement system, resulting in membrane lysis. These lysed tachyzoites **do not take up** the alkaline methylene blue dye (appearing colorless/unstained). * **Negative Result:** In the absence of antibodies, the tachyzoites remain intact and **stain blue**. **Analysis of Incorrect Options:** * **A. Leishmaniasis:** Diagnosis typically involves the Montenegro skin test (leishmanin test) or demonstrating LD bodies in bone marrow/splenic aspirates. * **B. Echinococcosis (Hydatid Disease):** Diagnosed via imaging (USG/CT showing "water lily sign") and serology like Casoni’s skin test (historical) or ELISA for Echinococcus antibodies. * **D. Balantidiasis:** Diagnosis is primarily made by identifying large ciliated trophozoites or cysts in stool samples (microscopy). **High-Yield Clinical Pearls for NEET-PG:** 1. **Gold Standard:** Although SFDT is the reference standard, it is rarely performed today because it requires live, infectious tachyzoites; ELISA is the preferred modern alternative. 2. **Congenital Toxoplasmosis:** Characterized by the classic triad: **Chorioretinitis, Hydrocephalus, and Intracranial calcifications.** 3. **Treatment:** The drug of choice for Toxoplasmosis is **Pyrimethamine + Sulfadiazine** (with Folinic acid to prevent bone marrow suppression).

Q: What parasite is associated with the appearance of rice grains in the stool due to the passage of proglottids?

Taenia saginata. **Explanation:** The correct answer is **Taenia saginata** (Beef Tapeworm). The hallmark clinical feature of *T. saginata* infection is the active migration of gravid proglottids through the anal sphincter. These proglottids are muscular, motile, and white, often described by patients as **"rice grains"** or "white ribbons" moving in the stool or found on undergarments. **Why Taenia saginata is correct:** Unlike other tapeworms, the proglottids of *T. saginata* are highly motile. A single gravid proglottid contains approximately 100,000 eggs and has 15–30 lateral uterine branches (a key diagnostic feature). Their independent motility allows them to crawl out of the anus, leading to the "rice grain" appearance. **Why other options are incorrect:** * **Taenia solium:** While it also sheds proglottids, they are less motile than *T. saginata* and have fewer lateral uterine branches (7–13). The primary clinical concern with *T. solium* is Cysticercosis. * **Diphyllobothrium latum:** This worm releases eggs through a uterine pore rather than shedding intact gravid proglottids. It is clinically associated with Vitamin B12 deficiency (Megaloblastic anemia). * **Hymenolepis nana:** This is the smallest tapeworm. The proglottids are tiny and usually disintegrate in the gastrointestinal tract before being passed, so they are not typically seen as "rice grains." **NEET-PG High-Yield Pearls:** * **Diagnostic Morphological Feature:** *T. saginata* has a scolex with 4 suckers but **no rostellum or hooks** (unarmed), whereas *T. solium* has both (armed). * **Intermediate Host:** Cow/Beef (*T. saginata*); Pig/Pork (*T. solium*). * **Treatment of Choice:** Praziquantel is the drug of choice for the intestinal stage of both species.

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.

Question 1

Which of the following is true regarding Wucheria bancrofti?

Accepted Answer

Tail tip free from nuclei

Answer

Unsheathed microfilaria

Answer

Non-periodic microfilaria

Answer

All of the above

Question 2

Man is the intermediate host for which of the following infections?

Accepted Answer

Malaria

Answer

Filaria

Answer

Dengue

Answer

Plague

Question 3

What is the most likely cause of a ring-enhancing lesion in an AIDS patient?

Accepted Answer

Toxoplasmosis

Answer

Cryptococcosis

Answer

Hydatid Cyst

Answer

Neurocysticercosis

Question 4

In a case of Plasmodium falciparum malaria, if the peripheral blood smear does not demonstrate trophozoites and schizonts, what is the most likely reason?

Accepted Answer

Infested red blood cells adhere to the capillaries of internal organs

Answer

Apoptosis of red blood cells due to hemozoin pigments

Answer

Lysis of red blood cells containing malarial parasites

Answer

Infested red blood cells are trapped in the spleen

Question 5

Regarding cutaneous amoebiasis, which statement is not true?

Accepted Answer

The infection reaches the skin through the bloodstream.

Answer

It is a spreading necrotizing inflammation of the skin and cutaneous tissue.

Answer

Rapid improvement with anti-amoebic treatment occurs.

Answer

It can occur in the perianal region.

Question 6

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

Accepted Answer

Toxoplasmosis

Answer

Leishmaniasis

Answer

Echinococcosis

Answer

Balantidiasis

Question 7

What parasite is associated with the appearance of rice grains in the stool due to the passage of proglottids?

Accepted Answer

Taenia saginata

Answer

Taenia solium

Answer

Diphyllobothrium latum

Answer

Hymenolepis nana

Question 8

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 9

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 10

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

Accepted Answer

Trichinella

Answer

Ascaris

Answer

Hookworm

Answer

Pinworm

Parasitology — MCQs

Parasitology — MCQs

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