Parasitology Practice Questions

Q: Which of the following is NOT true about amoebic liver abscess?

Larvae are seen.. Amoebic liver abscess (ALA) is caused by the protozoan parasite **_Entamoeba histolytica_**. Understanding its life cycle is crucial for answering this question. ### **Why "Larvae are seen" is the correct answer (False statement):** _Entamoeba histolytica_ is a **protozoan**, not a helminth (worm). Its life cycle consists only of two stages: the **infective cyst** and the **pathogenic trophozoite**. It does not have a larval stage. Therefore, seeing larvae in a liver abscess is impossible for amoebiasis; larvae would instead suggest a helminthic infection like Hydatid cyst (_Echinococcus granulosus_) or Ascariasis. ### **Analysis of other options:** * **Adult forms are seen:** In protozoology, the "adult" or vegetative stage is the **Trophozoite**. In ALA, trophozoites are found at the periphery of the abscess cavity (the advancing front), where they cause tissue necrosis. * **Conservative treatment is generally employed:** Most cases of ALA respond excellently to medical management with **Metronidazole** or Tinidazole. Surgical aspiration is rarely needed unless the abscess is very large (>10 cm), threatened to rupture, or fails to respond to drugs. * **Ultrasonography can aid in diagnosis:** USG is the first-line imaging modality. It typically shows a hypoechoic, round or oval lesion, usually in the **right lobe** of the liver. ### **High-Yield Clinical Pearls for NEET-PG:** * **Anchovy Sauce Pus:** The aspirated pus is typically reddish-brown, odorless, and sterile (contains no bacteria). * **Trophozoites** are found in the **pus wall**, not usually in the central necrotic debris. * **Route of spread:** From the colon to the liver via the **Portal Vein**. * **Diagnosis:** Stool microscopy is often negative for cysts/trophozoites in 60-90% of ALA cases; **Serology (IHA/ELISA)** is highly sensitive.

Q: A butcher, who is fond of eating raw hamburger, develops chorioretinitis. A Sabin-Feldman dye test is positive. This patient is most likely infected with which organism?

Toxoplasmosis. **Explanation:** The clinical presentation and diagnostic findings point directly to **Toxoplasmosis**, caused by the protozoan *Toxoplasma gondii*. **Why Toxoplasmosis is correct:** 1. **Transmission:** The patient is a butcher who eats raw hamburger. *T. gondii* is commonly transmitted via the ingestion of undercooked meat containing **tissue cysts** (bradyzoites) or food contaminated with oocysts from cat feces. 2. **Clinical Feature:** **Chorioretinitis** is a classic manifestation of toxoplasmosis, occurring in both congenital cases and as a reactivation in immunocompromised or occasionally immunocompetent adults. 3. **Diagnostic Gold Standard:** The **Sabin-Feldman Dye Test** is the definitive serological reference test for Toxoplasmosis. It measures IgG antibodies; if antibodies are present, they prevent methylene blue dye from staining the live *Toxoplasma* tachyzoites. **Why other options are incorrect:** * **Trichinosis (*Trichinella spiralis*):** Also associated with raw meat (usually pork), but typically presents with periorbital edema, severe myalgia, and eosinophilia, not chorioretinitis. * **Schistosomiasis:** A trematode infection acquired through skin penetration in contaminated water. It primarily affects the portal or venous system (causing hematuria or portal hypertension). * **Visceral Larva Migrans (*Toxocara canis*):** Caused by migrating dog roundworm larvae. While it can cause "Ocular Larva Migrans," the Sabin-Feldman test is specific only to *Toxoplasma*. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad (Congenital):** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Imaging:** In HIV patients, it presents as **ring-enhancing lesions** on brain CT/MRI. * **Treatment:** Pyrimethamine + Sulfadiazine (with Leucovorin/Folinic acid to prevent bone marrow suppression). * **Tachyzoites:** The active, replicating form seen in acute infections.

Q: What is the infective stage of hookworm?

Filiform larva. The correct answer is **B. Filiform larva** (specifically the **third-stage or L3 filariform larva**). ### **Educational Explanation** **1. Why Filiform Larva is Correct:** Hookworms (*Ancylostoma duodenale* and *Necator americanus*) follow a specific life cycle where eggs are passed in feces and hatch into non-infective rhabditiform larvae (L1) in the soil. After two molts, they transform into **filariform larvae (L3)**. This stage is characterized by a long, slender body and a closed mouth, making it non-feeding but highly motile. It is the only stage capable of penetrating intact human skin (usually the feet), which is the primary mode of infection. **2. Why Other Options are Incorrect:** * **A. Trophozoite form:** This is the active, feeding, and motile stage of **protozoa** (e.g., *Entamoeba histolytica* or *Giardia*). Helminths like hookworms do not have a trophozoite stage. * **C. Cyst:** This is the dormant, resistant stage of many **protozoa** (e.g., *E. histolytica*). While some nematodes have "encysted" larvae (like *Trichinella*), hookworms do not utilize a cyst for transmission. ### **High-Yield Clinical Pearls for NEET-PG** * **Mode of Entry:** Skin penetration (Ancylostoma can also be transmitted via ingestion/transmammary routes, but filariform larva remains the infective stage). * **Ground Itch:** An allergic reaction/dermatitis at the site of larval entry. * **Loeffler’s Syndrome:** Hookworms exhibit a **heart-lung migration**; larvae can cause transient pulmonary symptoms and eosinophilia. * **Pathogenesis:** Adult worms attach to the small intestine mucosa using buccal capsules (teeth/cutting plates) and suck blood, leading to **Microcytic Hypochromic Anemia** (Iron deficiency). * **Diagnosis:** Presence of non-bile stained, segmented eggs with a clear space between the shell and embryo in stool.

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.

Question 1

Which of the following is NOT true about amoebic liver abscess?

Accepted Answer

Larvae are seen.

Answer

Adult forms are seen.

Answer

Conservative treatment is generally employed.

Answer

Ultrasonography can aid in diagnosis.

Question 2

A butcher, who is fond of eating raw hamburger, develops chorioretinitis. A Sabin-Feldman dye test is positive. This patient is most likely infected with which organism?

Accepted Answer

Toxoplasmosis

Answer

Trichinosis

Answer

Schistosomiasis

Answer

Visceral larva migrans

Question 3

What is the infective stage of hookworm?

Accepted Answer

Filiform larva

Answer

Trophozoite form

Answer

Cyst

Answer

None of the above

Question 4

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 5

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

Accepted Answer

Malaria

Answer

Filaria

Answer

Dengue

Answer

Plague

Question 6

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 7

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 8

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 9

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 10

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

Parasitology — MCQs

Parasitology — MCQs

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