Parasitology Practice Questions

Q: Which test, performed on jejunal mucus, is used for the diagnosis of giardiasis?

Giardiasis. **Explanation:** The correct answer is **Giardiasis**. The test referred to in the question is the **Entero-test (String Test)**. **Why Giardiasis is correct:** *Giardia lamblia* primarily inhabits the duodenum and upper jejunum. In cases where routine stool examinations (for cysts or trophozoites) are negative but clinical suspicion remains high, the **Entero-test** is employed. In this procedure, a patient swallows a gelatin capsule containing a weighted nylon string. The string uncoils in the upper GI tract; after a few hours, it is withdrawn. The adherent **jejunal mucus** is then scraped from the string and examined microscopically for motile pear-shaped trophozoites. This is considered more sensitive than a single stool exam for detecting the parasite in the biliary tract or upper intestine. **Why other options are incorrect:** * **Amoebiasis:** *Entamoeba histolytica* primarily affects the colon (large intestine). Diagnosis is typically made via stool microscopy for quadrinucleate cysts/trophozoites or colonoscopic biopsy, not jejunal aspiration. * **Strongyloidiasis:** While *Strongyloides stercoralis* larvae can be found in the duodenum, the gold standard is stool examination (Baermann technique) or agar plate culture. The String Test can detect it, but it is classically associated with Giardia in exams. * **Cyclosporiasis:** This is diagnosed via stool examination using modified acid-fast staining to identify oocysts. **NEET-PG High-Yield Pearls:** * **Giardiasis** is the most common cause of water-borne parasitic diarrhea and causes **steatorrhea** (foul-smelling, floating stools) due to malabsorption. * It does **not** cause tissue invasion or hematogenous spread (no eosinophilia). * **Antigen detection (ELISA)** for GSA-65 is now preferred over the String Test due to being non-invasive. * **Drug of choice:** Tinidazole or Metronidazole.

Q: All of the following infections are caused by nematodes resulting from ingestion of infective eggs, except?

Strongyloides stercoralis. **Explanation:** The mode of transmission for intestinal nematodes is a high-yield topic for NEET-PG. These parasites are generally classified based on whether they infect humans via **ingestion of eggs** or **larval skin penetration**. **1. Why Strongyloides stercoralis is the correct answer:** Unlike the other options, *Strongyloides stercoralis* (Threadworm) is transmitted via the **penetration of intact skin** by **filariform larvae** (L3) present in contaminated soil. It does not involve the ingestion of eggs. A unique feature of *Strongyloides* is its ability for **autoinfection**, where rhabditiform larvae transform into filariform larvae within the host's intestine, leading to chronic infection and potentially fatal hyperinfection syndrome in immunocompromised patients. **2. Analysis of Incorrect Options (Transmission via Egg Ingestion):** The mnemonic **"EAT"** is commonly used to remember nematodes transmitted by egg ingestion: * **Ascaris lumbricoides (Roundworm):** Infection occurs by ingesting embryonated eggs from soil-contaminated food or water. * **Enterobius vermicularis (Pinworm):** Transmission is via ingestion of eggs, often through fof-hand contact (autoinfection) or contaminated linens. * **Trichuris trichiura (Whipworm):** Infection occurs through the ingestion of embryonated eggs from the soil. **3. NEET-PG Clinical Pearls:** * **Skin Penetrators:** Remember **"Strong Hook"** — *Strongyloides stercoralis* and Hookworms (*Ancylostoma duodenale*, *Necator americanus*). * **Larva Currens:** A pathognomonic rapidly moving serpiginous cutaneous eruption associated with *Strongyloides*. * **Diagnosis:** *Strongyloides* is diagnosed by finding **larvae** in stool, whereas *Ascaris*, *Trichuris*, and Hookworms are diagnosed by finding **eggs** in stool. * **Drug of Choice:** Ivermectin is the preferred treatment for *Strongyloides*, while Albendazole is used for most other intestinal nematodes.

Q: Pear-shaped trophozoite with an undulating membrane is a characteristic feature of which parasite?

Trichomonas Vaginalis. **Explanation:** The correct answer is **Trichomonas vaginalis**. This parasite is a flagellated protozoan characterized by a **pear-shaped (pyriform)** trophozoite. Its defining morphological features include four anterior flagella and a fifth flagellum that forms an **undulating membrane** extending halfway down the body. It also possesses a prominent axostyle that aids in attachment to epithelial cells. Notably, *T. vaginalis* exists only in the trophozoite stage; there is no cyst stage in its life cycle. **Analysis of Incorrect Options:** * **Giardia lamblia:** While also pear-shaped, it is characterized by a "falling leaf" motility, two nuclei (giving a "monkey-face" appearance), and four pairs of flagella. It lacks an undulating membrane. * **Trypanosoma brucei:** These are hemoflagellates. While they possess an undulating membrane, they are typically **spindle-shaped** or elongated (trypomastigotes) rather than pear-shaped. * **Enteromonas hominis:** This is a rare, non-pathogenic intestinal commensal. The trophozoite is oval or pear-shaped but is much smaller and lacks an undulating membrane. **Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Causes "Strawberry Cervix" (punctate hemorrhages) and a foul-smelling, yellowish-green frothy vaginal discharge. * **Diagnosis:** The gold standard is **Whiff test** (KOH) and **Wet mount microscopy** showing "jerky/twitching motility." Culture (Diamond’s medium) is the most sensitive method. * **Treatment:** Drug of choice is **Metronidazole**. Crucially, both partners must be treated simultaneously to prevent "ping-pong" reinfection.

Q: Which of the following is the only common pathogenic protozoan found in the duodenum and jejunum?

Giardia lamblia. **Explanation:** The correct answer is **Giardia lamblia**. **1. Why Giardia lamblia is correct:** *Giardia lamblia* (also known as *G. duodenalis* or *G. intestinalis*) is a flagellated protozoan that specifically inhabits the **duodenum and upper jejunum** of humans. It attaches to the mucosal epithelium using a ventral sucking disc. The alkaline environment of the duodenum is conducive to the excystation of cysts into trophozoites. It is the most common cause of parasitic diarrhea worldwide and is classically associated with malabsorption and steatorrhea (foul-smelling, fatty stools) because it coats the intestinal mucosa, interfering with fat absorption. **2. Why the other options are incorrect:** * **Entamoeba coli:** This is a non-pathogenic commensal protozoan that resides in the **large intestine** (colon). It is often confused with the pathogenic *E. histolytica*. * **Balantidium coli:** This is the largest protozoan and the only ciliate pathogenic to humans. It primarily inhabits the **large intestine** (cecum and colon), causing symptoms similar to amoebic dysentery. * **Toxoplasma gondii:** This is an obligate intracellular coccidian parasite. While infection occurs via the GI tract, it does not colonize the intestinal lumen; it disseminates to various tissues (brain, muscles, eyes) as tachyzoites and bradyzoites. **3. NEET-PG High-Yield Pearls:** * **Morphology:** Trophozoites are "pear-shaped" with a "falling leaf" motility and a characteristic "monkey face" appearance (two nuclei). * **Diagnosis:** Stool microscopy (cysts/trophozoites) or the **String Test (Entero-test)** to sample duodenal contents. * **Clinical:** Associated with **IgA deficiency**; causes malabsorption of fat and Vitamin B12. * **Treatment:** Drug of choice is **Tinidazole** or Metronidazole.

Q: What is the most common site for amebiasis?

Cecum. **Explanation:** **1. Why the Cecum is the Correct Answer:** *Entamoeba histolytica* primarily infects the large intestine. The **cecum and the ascending colon** are the most common sites for primary involvement. This is due to the **stasis of fecal contents** in these areas, which provides an ideal environment for the trophozoites to colonize the mucosa, multiply, and invade the tissue to form characteristic "flask-shaped" ulcers. **2. Analysis of Incorrect Options:** * **Sigmoid Colon (Option A):** While the sigmoid colon and rectum are frequently involved in chronic or severe cases (leading to dysentery), they are secondary in frequency to the cecal region. * **Transverse Colon (Option B):** This area is less commonly the primary site of infection compared to the proximal colon where the initial colonization occurs. * **Hepatic Flexure (Option D):** Although amebiasis can affect any part of the large bowel, the hepatic flexure is a less common site of primary localization than the cecum. **3. NEET-PG High-Yield Pearls:** * **Pathognomonic Lesion:** The "Flask-shaped ulcer" (narrow neck, broad base) is the hallmark of intestinal amebiasis. * **Most Common Extra-intestinal Site:** The **Liver** (Amebic Liver Abscess), typically involving the right lobe due to the portal blood flow from the superior mesenteric vein. * **Stool Microscopy:** Look for "Quadrinucleate cysts" (infective stage) or "Trophozoites with ingested RBCs" (diagnostic of invasive disease). * **Treatment of Choice:** Metronidazole or Tinidazole (for tissue-dwelling trophozoites) followed by a luminal amebicide like Paromomycin or Diloxanide furoate to clear cysts.

Q: Which is the only host for the organism described?

Trichuris trichiura. ***Trichuris trichiura*** - Humans are the **only host** for this whipworm, with a **direct lifecycle** requiring no intermediate host or vector. - Has characteristic **barrel-shaped eggs** with **bipolar hyaline plugs** and completes its entire development in the human intestine. *Dracunculus medinensis* - Requires **Cyclops** (water flea) as an **intermediate host** in freshwater sources for larval development. - Cannot complete its lifecycle with humans alone, making it dependent on the aquatic intermediate host. *Onchocerca volvulus* - Transmitted by **Simulium** (blackfly) which serves as both **vector** and **intermediate host**. - Requires the blackfly for larval development and transmission between human hosts. *Wuchereria bancrofti* - Uses **Culex**, **Aedes**, or **Anopheles** mosquitoes as **intermediate hosts** and vectors. - Cannot survive or reproduce without the mosquito intermediate host for larval development.

Q: Which of the following statements about filariasis is FALSE?

Man serves as the intermediate host.. In the life cycle of filarial parasites (such as *Wuchereria bancrofti*), **Man serves as the Definitive Host**, not the intermediate host. ### Why Option B is the Correct (False) Statement: In parasitology, the **Definitive Host** is defined as the host where the parasite reaches maturity and undergoes **sexual reproduction**. For filariasis, adult male and female worms mate in the human lymphatic system to produce microfilariae. The **Mosquito** (Culex, Anopheles, or Aedes) serves as the **Intermediate Host**, where larval development occurs without sexual reproduction. ### Explanation of Other Options: * **Option A (True):** The **Extrinsic Incubation Period** is the time taken for the parasite to develop from the L1 stage to the infective L3 stage within the mosquito. This typically takes **10–14 days**, depending on environmental temperature. * **Option C (True):** Adult worms specifically inhabit the **afferent lymphatic vessels** and lymph nodes, leading to the classic clinical presentation of lymphedema and elephantiasis. * **Option D (True):** Filariasis follows a **Cyclo-developmental** pattern in the vector. This means the parasite undergoes essential developmental changes (L1 → L2 → L3) but **does not multiply** in number within the mosquito. One microfilaria ingested results in only one infective larva. ### NEET-PG High-Yield Pearls: * **Infective Stage:** Third-stage larvae (**L3**). * **Diagnostic Stage:** Microfilariae in peripheral blood (usually collected at night due to **nocturnal periodicity**, 10 PM – 2 AM). * **Drug of Choice:** Diethylcarbamazine (DEC); however, it is contraindicated in Onchocerciasis due to the Mazzotti reaction. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough and high IgE levels.

Q: Which parasite is found in its amastigote form in humans?

Trypanosoma cruzi. **Explanation:** The correct answer is **Trypanosoma cruzi**. In medical parasitology, understanding the morphological stages of Hemoflagellates is high-yield for NEET-PG. **1. Why Trypanosoma cruzi is correct:** *T. cruzi* (the causative agent of **Chagas disease**) is unique among the human trypanosomes because it possesses an **intracellular amastigote stage**. After entering the human host through the bite of the Reduviid (Triatomine) bug, the parasite invades various tissues (especially cardiac muscle and the myenteric plexus). Inside these cells, it loses its flagellum and transforms into the **amastigote** form to multiply by binary fission. It is also found in the blood as a C-shaped or U-shaped **trypomastigote**. **2. Why the other options are incorrect:** * **Trypanosoma brucei (gambiense and rhodesiense):** These are the causative agents of **African Sleeping Sickness**. Unlike *T. cruzi*, these parasites exist **only in the extracellular form** in the human host. They multiply in the blood, lymph, and spinal fluid as **trypomastigotes**. They **do not** have an amastigote stage in humans. **3. High-Yield NEET-PG Clinical Pearls:** * **Morphology Rule:** *Leishmania* and *T. cruzi* are the two major hemoflagellates that exhibit the amastigote form in humans (LD bodies in *Leishmania*). * **Chagas Disease Triad:** Look for **Romaña’s sign** (unilateral painless periorbital edema), **Megaesophagus/Megacolon**, and **Dilated Cardiomyopathy**. * **Vector:** *T. cruzi* is transmitted by the "Kissing bug" (Reduviid bug) via posterior station inoculation (feces), whereas African Trypanosomes are transmitted by the **Tsetse fly** via anterior station (saliva).

Q: Which parasitic infection is capable of producing spinal cord compression?

Echinococcosis. **Explanation:** **Echinococcosis (Hydatid Disease)**, caused by the larval stage of *Echinococcus granulosus*, is the correct answer. While the liver (75%) and lungs (15%) are the most common sites for hydatid cysts, **bone involvement** occurs in approximately 1–2% of cases. The spine is the most frequent site of skeletal involvement (50% of bone cases). Unlike in soft tissues, the cyst in the bone lacks a pericyst, allowing it to grow aggressively and infiltrate the vertebral column. This leads to vertebral destruction, pathological fractures, or direct expansion into the spinal canal, resulting in **spinal cord compression** and paraplegia. **Analysis of Incorrect Options:** * **Leishmaniasis:** Primarily affects the reticuloendothelial system (Visceral) or skin/mucosa (Cutaneous). It does not form space-occupying cystic lesions in the spine. * **Wuchereriasis:** Caused by *Wuchereria bancrofti*, it involves the lymphatic system leading to lymphedema and elephantiasis, not skeletal or spinal destruction. * **Amoebiasis:** *Entamoeba histolytica* typically causes intestinal ulcers or liver abscesses. While rare brain abscesses occur, spinal cord compression is not a recognized clinical feature. **High-Yield Clinical Pearls for NEET-PG:** * **"Water Lily Sign"** and **"Camelot Sign"** are classic radiological findings of ruptured hydatid cysts on USG/CT. * **Casoni’s Test:** An immediate hypersensitivity skin test (now largely replaced by serology like ELISA). * **Treatment:** Surgical excision is the mainstay, often supplemented with **Albendazole**. * **PAIR Technique:** (Puncture, Aspiration, Injection, Re-aspiration) is used for hepatic cysts but is generally avoided in spinal cases due to the risk of anaphylaxis and seeding.

Q: Human filariasis is caused by which of the following organisms?

Wuchereria Bancrofti. **Explanation:** **Wuchereria bancrofti** is the correct answer because it is the primary causative agent of **Lymphatic Filariasis**, accounting for approximately 90% of cases globally and the vast majority in India. The disease is characterized by the obstruction of lymphatic vessels by adult worms, leading to lymphedema and elephantiasis. In India, the primary vector for *W. bancrofti* is the *Culex quinquefasciatus* mosquito. **Analysis of Incorrect Options:** * **Loa-loa:** Causes "African Eye Worm" or Loiasis. It is characterized by Calabar swellings and the migration of adult worms across the subconjunctiva of the eye, rather than classic lymphatic obstruction. * **Onchocerca volvulus:** Causes "River Blindness" (Onchocerciasis). It is transmitted by the Blackfly (*Simulium*) and primarily affects the skin and eyes, leading to severe itching and visual impairment. * **Brugia malayi:** While it also causes lymphatic filariasis, it is less common than *W. bancrofti*. In India, it is restricted to specific pockets (e.g., Kerala). It typically causes lymphedema below the knee and rarely involves the genitals. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Diethylcarbamazine (DEC) is the standard treatment. However, in Global Elimination programs (GPELF), a triple drug therapy (**IDA**: Ivermectin, DEC, and Albendazole) is now recommended. * **Nocturnal Periodicity:** Microfilariae of *W. bancrofti* usually circulate in peripheral blood at night (10 PM – 2 AM), coinciding with the biting habits of the *Culex* mosquito. * **Diagnosis:** The "Gold Standard" is the demonstration of microfilariae in a peripheral blood smear. * **National Target:** India aims for the **elimination** of Lymphatic Filariasis (defined as <1% microfilaria rate in all sentinel sites).

Question 1

Which test, performed on jejunal mucus, is used for the diagnosis of giardiasis?

Accepted Answer

Giardiasis

Answer

Amoebiasis

Answer

Strongyloidiasis

Answer

Cyclosporiasis

Question 2

All of the following infections are caused by nematodes resulting from ingestion of infective eggs, except?

Accepted Answer

Strongyloides stercoralis

Answer

Ascaris lumbricoides

Answer

Enterobius vermicularis

Answer

Trichuris trichura

Question 3

Pear-shaped trophozoite with an undulating membrane is a characteristic feature of which parasite?

Accepted Answer

Trichomonas Vaginalis

Answer

Giardia lamblia

Answer

Trypanosoma brucei (African trypanosomiasis)

Answer

Enteromonas hominis

Question 4

Which of the following is the only common pathogenic protozoan found in the duodenum and jejunum?

Accepted Answer

Giardia lamblia

Answer

Entamoeba coli

Answer

Balantidium coli

Answer

Toxoplasma gondii

Question 5

What is the most common site for amebiasis?

Accepted Answer

Cecum

Answer

Sigmoid colon

Answer

Transverse colon

Answer

Hepatic flexure

Question 6

Which is the only host for the organism described?

Accepted Answer

Trichuris trichiura

Answer

Dracunculus medinensis

Answer

Onchocerca volvulus

Answer

Wuchereria bancrofti

Question 7

Which of the following statements about filariasis is FALSE?

Accepted Answer

Man serves as the intermediate host.

Answer

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 8

Which parasite is found in its amastigote form in humans?

Accepted Answer

Trypanosoma cruzi

Answer

Trypanosoma brucei

Answer

Trypanosoma gambiense

Answer

Trypanosoma rhodesiense

Question 9

Which parasitic infection is capable of producing spinal cord compression?

Accepted Answer

Echinococcosis

Answer

Leishmaniasis

Answer

Wuchereriasis

Answer

Amoebiasis

Question 10

Human filariasis is caused by which of the following organisms?

Accepted Answer

Wuchereria Bancrofti

Answer

Loa-loa

Answer

Onchocerca Volvulus

Answer

Brugia Malayi

Parasitology — MCQs

Parasitology — MCQs

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