Parasitology — MCQs
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Pear-shaped trophozoite with an undulating membrane is a characteristic feature of which parasite?
Which of the following is the only common pathogenic protozoan found in the duodenum and jejunum?
What is the most common site for amebiasis?
Which is the only host for the organism described?
Which of the following statements about filariasis is FALSE?
Which parasite is found in its amastigote form in humans?
Which parasitic infection is capable of producing spinal cord compression?
Which of the following is associated with bile duct carcinoma?
Which of the following parasites requires two hosts?
A pregnant woman on her second pre-natal visit is suspected to have an infection. Her pet cat could act as a reservoir for which of the following conditions?
Parasitology Indian Medical PG Practice Questions and MCQs
Question 91: Pear-shaped trophozoite with an undulating membrane is a characteristic feature of which parasite?
- A. Trichomonas Vaginalis (Correct Answer)
- B. Giardia lamblia
- C. Trypanosoma brucei (African trypanosomiasis)
- D. Enteromonas hominis
Explanation: **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.
Question 92: Which of the following is the only common pathogenic protozoan found in the duodenum and jejunum?
- A. Entamoeba coli
- B. Balantidium coli
- C. Giardia lamblia (Correct Answer)
- D. Toxoplasma gondii
Explanation: **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.
Question 93: What is the most common site for amebiasis?
- A. Sigmoid colon
- B. Transverse colon
- C. Cecum (Correct Answer)
- D. Hepatic flexure
Explanation: **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.
Question 94: Which is the only host for the organism described?
- A. Dracunculus medinensis
- B. Onchocerca volvulus
- C. Wuchereria bancrofti
- D. Trichuris trichiura (Correct Answer)
Explanation: ***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.
Question 95: Which of the following statements about filariasis is FALSE?
- A. Extrinsic incubation period is 10-14 days.
- B. Man serves as the intermediate host. (Correct Answer)
- C. Adult worms reside in the lymphatics of the host.
- D. There is no multiplication of the parasite within the mosquito vector.
Explanation: 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.
Question 96: Which parasite is found in its amastigote form in humans?
- A. Trypanosoma cruzi (Correct Answer)
- B. Trypanosoma brucei
- C. Trypanosoma gambiense
- D. Trypanosoma rhodesiense
Explanation: **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).
Question 97: Which parasitic infection is capable of producing spinal cord compression?
- A. Leishmaniasis
- B. Wuchereriasis
- C. Echinococcosis (Correct Answer)
- D. Amoebiasis
Explanation: **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.
Question 98: Which of the following is associated with bile duct carcinoma?
- A. Clonorchis
- B. Opisthorchis
- C. E. granulosus
- D. Both Clonorchis and Opisthorchis (Correct Answer)
Explanation: **Explanation:** The correct answer is **Both Clonorchis and Opisthorchis**. **1. Why the correct answer is right:** *Clonorchis sinensis* (Chinese liver fluke) and *Opisthorchis viverrini/felineus* (Southeast Asian liver flukes) are trematodes that inhabit the distal bile ducts. Chronic infection leads to mechanical irritation, chronic inflammation, and the release of parasite-derived mitogenic factors. This persistent biliary damage induces adenomatous hyperplasia and cellular dysplasia, which are precursors to **Cholangiocarcinoma (Bile duct carcinoma)**. Both parasites are classified as Group 1 carcinogens by the IARC. **2. Why the other options are incorrect:** * **Echinococcus granulosus:** This cestode causes **Hydatid cyst** disease, primarily in the liver. While it can cause complications like cyst rupture or biliary obstruction, it is not associated with malignancy or bile duct carcinoma. * **Clonorchis/Opisthorchis alone:** While both are independent risk factors, selecting only one would be incomplete, as both share the same pathogenic mechanism regarding biliary oncogenesis. **3. NEET-PG High-Yield Clinical Pearls:** * **Infective Stage:** Metacercariae (found in undercooked freshwater fish). * **Intermediate Hosts:** 1st host is a Snail; 2nd host is a Cyprinoid fish. * **Diagnosis:** Stool microscopy for characteristic "operculated eggs" (often described as having a "shouldered" appearance). * **Drug of Choice:** Praziquantel. * **Other Parasite-Cancer Associations:** *Schistosoma haematobium* is strongly associated with **Squamous Cell Carcinoma of the Urinary Bladder**.
Question 99: Which of the following parasites requires two hosts?
- A. Taenia solium (Correct Answer)
- B. Entamoeba histolytica
- C. Taenia saginata
- D. Giardia
Explanation: ### Explanation The correct answer is **Taenia solium** (and notably **Taenia saginata**, though the question structure implies a specific focus on the life cycle requirements). **1. Why Taenia solium is correct:** *Taenia solium* (Pork tapeworm) is a **digenetic parasite**, meaning it requires two hosts to complete its life cycle: * **Definitive Host:** Humans (harbor the adult worm in the small intestine). * **Intermediate Host:** Pigs (harbor the larval stage, *Cysticercus cellulosae*). * **Note on Option C:** *Taenia saginata* also requires two hosts (Humans and Cattle). In many NEET-PG questions, if both are present, the question may be flawed or looking for the one most associated with "Cysticercosis" in humans (where humans can act as accidental intermediate hosts for *T. solium* but not *T. saginata*). **2. Why the other options are incorrect:** * **Entamoeba histolytica:** A monoxenous parasite. It requires only **one host** (Humans). Transmission occurs via the feco-oral route through ingestion of mature quadrinucleate cysts. * **Giardia lamblia:** Also a monoxenous parasite requiring only **one host** (Humans). It exists in two stages: trophozoite and cyst, with the cyst being the infective form. **3. NEET-PG Clinical Pearls:** * **Autoinfection:** *T. solium* is unique because humans can serve as both the definitive and intermediate host. Ingestion of eggs (via contaminated food or autoinfection) leads to **Cysticercosis**, most commonly manifesting as **Neurocysticercosis** (the leading cause of adult-onset seizures in India). * **Infective Stages:** * To get Intestinal Taeniasis: Eat undercooked pork containing *Cysticerci*. * To get Cysticercosis: Ingest *T. solium* eggs. * **High-Yield Distinction:** *T. saginata* has more uterine branches (15–30) than *T. solium* (7–13) and lacks a rostellum/hooks (unarmed).
Question 100: A pregnant woman on her second pre-natal visit is suspected to have an infection. Her pet cat could act as a reservoir for which of the following conditions?
- A. Toxoplasma gondii (Correct Answer)
- B. Rabies
- C. Streptocerca infection
- D. Plague
Explanation: ### Explanation **Correct Answer: A. Toxoplasma gondii** **Reasoning:** *Toxoplasma gondii* is an obligate intracellular protozoan for which members of the **Felidae family (cats)** are the only definitive hosts. Cats shed infective **oocysts** in their feces. Humans (intermediate hosts) typically acquire the infection through the ingestion of soil, water, or vegetables contaminated with these oocysts, or by handling cat litter. In pregnancy, primary infection is critical because the parasite can cross the placenta (**transplacental transmission**), leading to **Congenital Toxoplasmosis**. This can result in the classic triad of chorioretinitis, hydrocephalus, and intracranial calcifications. **Why the other options are incorrect:** * **B. Rabies:** While cats can transmit Rabies, they are considered **accidental hosts** (vectors), not the primary reservoir. The primary reservoirs are wild animals (bats, raccoons) and stray dogs. * **C. Streptocerca infection:** *Mansonella streptocerca* is a filarial nematode transmitted by **biting midges** (*Culicoides*). Humans and primates are the reservoirs, not cats. * **D. Plague:** Caused by *Yersinia pestis*, the primary reservoirs are **wild rodents** (e.g., rats, ground squirrels). Cats can occasionally contract plague and transmit it to humans via respiratory droplets or fleas, but they are not the natural reservoir. **High-Yield NEET-PG Pearls:** * **Definitive Host:** Cat (sexual cycle occurs here). * **Intermediate Host:** Humans/Birds/Rodents (asexual cycle). * **Infective forms:** Oocysts (from cat feces) or Bradyzoites (in undercooked meat). * **Diagnosis:** Sabin-Feldman Dye Test (Gold Standard) or IgM/IgG serology. * **Treatment in Pregnancy:** **Spiramycin** is used to prevent transmission to the fetus; if the fetus is already infected, Pyrimethamine and Sulfadiazine are used (after the first trimester).
Practice by Chapter
Classification of Parasites
Practice Questions
Intestinal Protozoa
Practice Questions
Blood and Tissue Protozoa
Practice Questions
Malaria Parasites
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Leishmaniasis
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Intestinal Helminths: Nematodes
Practice Questions
Tissue Nematodes
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Trematodes
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Cestodes
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Ectoparasites
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Antiparasitic Drugs
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Laboratory Diagnosis of Parasitic Infections
Practice Questions
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