Parasitology — MCQs
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What is the most common extrahepatic complication of amoebic hepatitis?
Which disease is transmitted by lice?
Oocyst of Toxoplasma gondii is found in which host?
An anxious mother brought her 4-year-old daughter to the pediatrician. The girl was passing loose, bulky stools for the past 20 days, often associated with abdominal pain. Stool examination showed pear-shaped, flagellated trophozoites and cysts with four nuclei. What is the likely causative organism?
What is the definitive host for Echinococcus granulosus?
Ziemann dots are seen in which Plasmodium species?
What is the diagnostic test of choice for extra-intestinal invasive amoebiasis?
Which of the following is NOT part of the classic triad of congenital toxoplasmosis?
Man serves as both the intermediate and definitive host for which of the following parasites?
Hydatid cyst is caused by which organism?
Parasitology Indian Medical PG Practice Questions and MCQs
Question 201: What is the most common extrahepatic complication of amoebic hepatitis?
- A. Meningitis
- B. Lung abscess (Correct Answer)
- C. Nephritis
- D. Encephalitis
Explanation: **Explanation:** Amoebic liver abscess (ALA), caused by *Entamoeba histolytica*, is the most common extra-intestinal manifestation of amoebiasis. When complications occur, they usually result from the direct extension or rupture of the abscess into adjacent structures. **1. Why Lung Abscess is Correct:** The liver is situated immediately below the diaphragm. The most common route of spread for an amoebic liver abscess is **direct extension through the diaphragm** into the thoracic cavity. This leads to pleuropulmonary amoebiasis, manifesting most frequently as a **lung abscess** (typically in the lower lobe of the right lung) or an empyema. Patients often present with a "chocolate-sauce" or "anchovy-paste" sputum if a hepatobronchial fistula forms. **2. Why Other Options are Incorrect:** * **Meningitis & Encephalitis:** While *E. histolytica* can spread hematogenously to the brain causing cerebral amoebiasis, this is extremely rare (less than 1% of cases) and usually occurs as a terminal event. (Note: Primary Amoebic Meningoencephalitis is caused by *Naegleria fowleri*, not *E. histolytica*). * **Nephritis:** Renal involvement in amoebiasis is exceptionally rare and is not a recognized standard complication of amoebic hepatitis. **Clinical Pearls for NEET-PG:** * **Most common site of ALA:** Right lobe of the liver (due to the bulk of tissue and portal blood flow distribution). * **Characteristic Pus:** Described as **"Anchovy sauce" appearance** (consists of liquefied hepatocytes and blood, but notably lacks host inflammatory cells/neutrophils). * **Diagnosis:** Serology (ELISA) is highly sensitive; Ultrasound is the initial imaging of choice. * **Treatment:** Drug of choice is **Metronidazole** followed by a luminal amoebicide (e.g., Diloxanide furoate) to eradicate the intestinal cyst stage.
Question 202: Which disease is transmitted by lice?
- A. Plague
- B. Kyasanur Forest Disease (KFD)
- C. Onchocerciasis
- D. Typhus fever (Correct Answer)
Explanation: **Explanation:** The correct answer is **Typhus fever**, specifically **Epidemic Typhus**, which is caused by *Rickettsia prowazekii*. This pathogen is transmitted by the **human body louse** (*Pediculus humanus corporis*). The transmission occurs when louse feces containing the bacteria are rubbed into bite wounds or mucous membranes by the host while scratching. **Analysis of Options:** * **Plague:** Caused by *Yersinia pestis*, this is primarily transmitted by the **rat flea** (*Xenopsylla cheopis*). * **Kyasanur Forest Disease (KFD):** This is a viral hemorrhagic fever transmitted by **Hard ticks** (*Haemaphysalis spinigera*). * **Onchocerciasis (River Blindness):** Caused by the nematode *Onchocerca volvulus*, it is transmitted by the bite of the **Blackfly** (*Simulium* species). **High-Yield Clinical Pearls for NEET-PG:** * **Louse-borne diseases (The "Louse Trio"):** 1. **Epidemic Typhus** (*R. prowazekii*) 2. **Relapsing Fever** (*Borrelia recurrentis*) 3. **Trench Fever** (*Bartonella quintana*) * **Brill-Zinsser Disease:** This is a recrudescent form of Epidemic Typhus that occurs years after the primary infection, acting as a reservoir for the bacteria. * **Scrub Typhus** (often confused with Epidemic Typhus) is transmitted by **trombiculid mites (chiggers)**, not lice. * **Treatment:** Doxycycline is the drug of choice for all rickettsial infections, including Typhus fever.
Question 203: Oocyst of Toxoplasma gondii is found in which host?
- A. Cat (Correct Answer)
- B. Dog
- C. Mosquito
- D. Cow
Explanation: **Explanation:** The life cycle of *Toxoplasma gondii* involves two types of hosts: definitive and intermediate. The correct answer is **Cat** because members of the family Felidae are the only **definitive hosts** for this parasite. 1. **Why Cat is correct:** Sexual reproduction (gametogony) of *T. gondii* occurs exclusively within the intestinal epithelial cells of cats. This process results in the formation of **oocysts**, which are then excreted in the cat's feces. These oocysts undergo sporulation in the environment to become infectious. 2. **Why other options are incorrect:** * **Dog and Cow:** These are **intermediate hosts**. In these animals (and humans), only asexual reproduction occurs, leading to the formation of tachyzoites and tissue cysts (bradyzoites). They do not produce oocysts. * **Mosquito:** Mosquitoes are vectors for parasites like *Plasmodium* (Malaria) or *Wuchereria bancrofti*, but they play no role in the transmission of Toxoplasmosis. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Stages:** Humans acquire infection via ingestion of **sporulated oocysts** (from cat feces/soil) or **tissue cysts** (undercooked meat). * **Congenital Toxoplasmosis:** Presents with the classic triad: **Chorioretinitis, Hydrocephalus, and Intracranial calcifications.** * **Diagnosis:** Sabin-Feldman Dye Test is the gold standard (though rarely used now). Tachyzoites are typically crescent-shaped. * **Treatment:** The drug of choice is a combination of **Pyrimethamine and Sulfadiazine**.
Question 204: An anxious mother brought her 4-year-old daughter to the pediatrician. The girl was passing loose, bulky stools for the past 20 days, often associated with abdominal pain. Stool examination showed pear-shaped, flagellated trophozoites and cysts with four nuclei. What is the likely causative organism?
- A. Entamoeba histolytica
- B. Giardia lamblia (Correct Answer)
- C. Cryptosporidium
- D. E. coli
Explanation: ### Explanation The clinical presentation and morphology described are classic for **Giardiasis**, caused by **_Giardia lamblia_** (also known as *G. duodenalis* or *G. intestinalis*). **Why Option B is Correct:** * **Clinical Presentation:** The patient has chronic diarrhea (20 days) characterized as "bulky" and "loose." This suggests **malabsorption** and steatorrhea, which occurs because *Giardia* trophozoites coat the duodenal mucosa, leading to the blunting of villi. * **Morphology:** The description of **pear-shaped, flagellated trophozoites** (often described as having a "falling leaf" motility and a "monkey face" appearance) and **cysts with four nuclei** is pathognomonic for *Giardia*. **Why Other Options are Incorrect:** * **A. *Entamoeba histolytica*:** Causes amoebic dysentery (bloody stools). Trophozoites are not flagellated and typically show ingested RBCs; cysts have 1–4 nuclei but a different internal structure (chromatoid bodies). * **C. *Cryptosporidium*:** Typically causes profuse watery diarrhea. It is diagnosed via modified acid-fast staining showing red-stained oocysts; it does not have a flagellated trophozoite stage. * **D. *E. coli*:** While certain strains (like EPEC) cause childhood diarrhea, they are bacteria, not protozoa, and would not present with flagellated trophozoites or quadrinucleated cysts in a stool ova and parasite exam. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Primarily the **duodenum** and upper jejunum (acidic pH). * **Diagnosis:** Stool microscopy is standard, but **Entero-test (String test)** can be used if stool is negative. * **Antigen Detection:** Immunochromatographic tests for Giardia-specific antigen 65 (GSA 65) are highly sensitive. * **Treatment:** Drug of choice is **Tinidazole** (single dose) or Metronidazole. * **Association:** Increased incidence in patients with **Selective IgA deficiency**.
Question 205: What is the definitive host for Echinococcus granulosus?
- A. Man
- B. Sheep
- C. Hound
- D. Dog (Correct Answer)
Explanation: **Explanation:** *Echinococcus granulosus*, also known as the dog tapeworm, causes **Cystic Echinococcosis (Hydatid disease)**. Understanding its life cycle is crucial for NEET-PG: 1. **Why Dog is the Correct Answer:** In parasitology, the **definitive host** is the one that harbors the adult stage of the parasite or where sexual reproduction occurs. For *E. granulosus*, the adult worm lives in the small intestine of **dogs** (and other canids like wolves). Eggs are passed in the dog's feces, which then infect the intermediate hosts. 2. **Analysis of Incorrect Options:** * **Man (Option A):** Humans act as **accidental, dead-end intermediate hosts**. Infection occurs via the feco-oral route (ingesting eggs). In humans, the parasite exists only in the larval stage (hydatid cyst), and since humans are not eaten by dogs, the cycle ends here. * **Sheep (Option B):** Sheep are the **natural intermediate hosts**. They ingest eggs from contaminated pastures, and the larval cysts develop in their organs (liver/lungs). The cycle is completed when a dog consumes the infected offal of a sheep. * **Hound (Option C):** While a hound is a type of dog, "Dog" is the standard taxonomic and textbook answer used in exams to represent the primary definitive host. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site:** Liver (60-70%), followed by Lungs. * **Diagnostic Sign:** "Water lily sign" or "Camelot sign" on imaging (due to detached germinal membranes). * **Casoni Test:** An immediate hypersensitivity skin test (now largely replaced by ELISA). * **Management:** **PAIR** (Puncture, Aspiration, Injection, Re-aspiration) technique. * **Drug of Choice:** Albendazole. * **Risk:** Rupture of the cyst can lead to fatal **anaphylaxis**.
Question 206: Ziemann dots are seen in which Plasmodium species?
- A. P. Vivax
- B. P. Falciparum
- C. P. Malariae (Correct Answer)
- D. P. Ovale
Explanation: **Explanation:** The correct answer is **C. P. Malariae**. In parasitology, "stippling" refers to the characteristic morphological changes (dots) seen in the cytoplasm of infected Red Blood Cells (RBCs) on a peripheral smear. These dots are essential for species identification. **1. Why P. Malariae is correct:** * **Ziemann’s dots** are fine, pinkish-to-lavender dust-like granules that appear in the cytoplasm of RBCs infected with *Plasmodium malariae*. These dots are typically harder to visualize than those in other species and often require prolonged staining. **2. Analysis of Incorrect Options:** * **A. P. Vivax:** Characterized by **Schüffner’s dots**. These are fine, round, pinkish-yellow granules. Infected RBCs are also typically enlarged (hypertrophied). * **B. P. Falciparum:** Characterized by **Maurer’s dots** (or Maurer’s clefts). These are coarse, irregular, dark-red spots seen in the cytoplasm of infected RBCs. * **D. P. Ovale:** Also shows **Schüffner’s dots** (sometimes specifically called James's dots). The RBCs are often oval-shaped with fimbriated (tufted) edges. **3. NEET-PG High-Yield Pearls:** * **RBC Age Preference:** *P. vivax/ovale* prefer young RBCs (reticulocytes); *P. malariae* prefers old RBCs; *P. falciparum* is "indiscriminate" (infects all ages), leading to high parasitemia. * **Morphology of P. Malariae:** Look for **"Band forms"** (trophozoites) and **"Daisy head/Rosette"** appearance (schizonts). * **Clinical Feature:** *P. malariae* causes **Quartan malaria** (fever every 72 hours) and is associated with **Nephrotic Syndrome** (Quartan Malarial Nephropathy).
Question 207: What is the diagnostic test of choice for extra-intestinal invasive amoebiasis?
- A. Counter immuno-electrophoresis
- B. Complement fixation test
- C. ELISA (Correct Answer)
- D. Indirect haemagglutination test
Explanation: **Explanation:** In **extra-intestinal invasive amoebiasis** (most commonly Amoebic Liver Abscess), the parasite *Entamoeba histolytica* is no longer confined to the intestinal lumen. Therefore, stool microscopy is often negative (only 15-30% sensitivity). Diagnosis relies heavily on detecting specific antibodies in the serum. **1. Why ELISA is the Correct Answer:** **ELISA (Enzyme-Linked Immunosorbent Assay)** is currently the **diagnostic test of choice** because it is highly sensitive (95-99%) and specific. It is preferred in clinical practice because it is rapid, cost-effective, and can detect both IgG and IgM antibodies. A positive ELISA for amoebic antibodies in a patient with clinical symptoms and imaging (like USG/CT) confirming a liver abscess is diagnostic. **2. Analysis of Incorrect Options:** * **A. Counter immuno-electrophoresis (CIEP):** While specific, it is technically demanding and has been largely replaced by ELISA in modern laboratories. * **B. Complement fixation test (CFT):** This is an older technique with lower sensitivity and is no longer used for routine diagnosis of amoebiasis. * **C. Indirect haemagglutination test (IHA):** IHA is very sensitive but lacks specificity because antibodies can persist for years after the infection has resolved, making it difficult to distinguish between past and current infection. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for Antigen Detection:** ELISA for **Gal/GalNAc lectin** in stool or pus (highly specific for *E. histolytica* vs. *E. dispar*). * **Amoebic Liver Abscess (ALA) Pus:** Classically described as **"Anchovy sauce"** appearance (odorless, chocolate-brown). * **Microscopy:** Look for **trophozoites with ingested RBCs** (Erythrophagocytosis), which is pathognomonic for invasive *E. histolytica*. * **Treatment of Choice:** Metronidazole or Tinidazole, followed by a luminal amoebicide (e.g., Diloxanide furoate or Paromomycin) to eradicate the carrier state.
Question 208: Which of the following is NOT part of the classic triad of congenital toxoplasmosis?
- A. Intracranial calcification
- B. Chorioretinitis
- C. Coagulopathy (Correct Answer)
- D. Hydrocephalus
Explanation: The classic triad of congenital toxoplasmosis is a high-yield topic for NEET-PG, representing the hallmark clinical presentation of *Toxoplasma gondii* infection acquired in utero. ### **Explanation of the Correct Answer** **C. Coagulopathy** is the correct answer because it is **not** part of the classic triad. While severe congenital infections can sometimes lead to systemic issues like thrombocytopenia or jaundice, coagulopathy is not a defining or pathognomonic feature of this specific parasitic infection. ### **Analysis of the Classic Triad (Incorrect Options)** The classic triad, also known as **Sabin’s Triad**, consists of: * **A. Intracranial Calcification:** These are typically **diffuse** and scattered throughout the brain parenchyma (unlike CMV, where calcifications are characteristically periventricular). * **B. Chorioretinitis:** This is the most common manifestation and can lead to permanent vision loss. It often presents as "salt and pepper" scarring on fundoscopy. * **D. Hydrocephalus:** Resulting from obstructive lesions (often aqueductal stenosis) caused by the inflammatory response to the parasite. ### **Clinical Pearls for NEET-PG** * **Transmission:** Risk of transmission is highest in the **third trimester**, but the severity of fetal damage is greatest if the infection is acquired in the **first trimester**. * **Diagnosis:** The gold standard for fetal diagnosis is **PCR of amniotic fluid**. In neonates, persistence of **IgG** beyond 12 months or the presence of **IgM/IgG** confirms the diagnosis. * **Treatment:** The standard regimen is **Pyrimethamine, Sulfadiazine, and Folinic acid** (Leucovorin) for one year. * **Prevention:** Pregnant women should avoid raw meat and contact with **cat litter** (oocysts).
Question 209: Man serves as both the intermediate and definitive host for which of the following parasites?
- A. Taenia solium (Correct Answer)
- B. Taenia saginata
- C. Diphyllobothrium latum
- D. Dicrocoelium dendriticum
Explanation: **Explanation:** In parasitology, the **definitive host** is where the parasite reaches sexual maturity (adult stage), while the **intermediate host** is where the larval or asexual stages develop. **Taenia solium (Pork Tapeworm)** is unique because humans can play both roles: 1. **Definitive Host:** Occurs when humans ingest undercooked pork containing **cysticerci**. The larvae develop into adult tapeworms in the small intestine (**Intestinal Taeniasis**). 2. **Intermediate Host:** Occurs when humans ingest **eggs** (via feco-oral route or autoinfection). The eggs hatch into oncospheres that penetrate the intestinal wall and migrate to tissues (brain, muscles) to form cysticerci, leading to **Cysticercosis**. **Analysis of Incorrect Options:** * **B. Taenia saginata (Beef Tapeworm):** Humans are **only** definitive hosts. Cattle serve as the intermediate host. Ingesting eggs does not cause cysticercosis in humans. * **C. Diphyllobothrium latum (Fish Tapeworm):** Humans are definitive hosts. It requires two intermediate hosts: Cyclops (1st) and freshwater fish (2nd). * **D. Dicrocoelium dendriticum (Lancet Liver Fluke):** Humans are accidental definitive hosts. Intermediate hosts are snails and ants. **High-Yield NEET-PG Pearls:** * **Other parasites** where man acts as both hosts: *Hymenolepis nana*, *Strongyloides stercoralis*, and *Trichinella spiralis*. * **Neurocysticercosis (NCC):** The most common cause of adult-onset seizures in India; caused by *T. solium* eggs, **not** by eating pork. * **Diagnosis:** Stool microscopy for eggs/proglottids (Taeniasis) and MRI/CT "starry sky appearance" (Cysticercosis).
Question 210: Hydatid cyst is caused by which organism?
- A. Clonorchis sinensis
- B. Wuchereria bancrofti
- C. Echinococcus granulosus (Correct Answer)
- D. Ascaris lumbricoides
Explanation: ### Explanation **Correct Answer: C. Echinococcus granulosus** **Echinococcus granulosus**, also known as the **Dog Tapeworm**, is the causative agent of **Cystic Echinococcosis (Hydatid Disease)**. In this life cycle, dogs are the definitive hosts, while humans act as accidental intermediate hosts. Upon ingestion of eggs (via contaminated food or water), larvae hatch in the duodenum, penetrate the intestinal wall, and enter the portal circulation. They most commonly lodge in the **liver (60-70%)**, followed by the lungs, where they develop into slow-growing, fluid-filled "Hydatid cysts." These cysts contain an inner germinal layer that produces "brood capsules" and "daughter cysts." **Why the other options are incorrect:** * **A. Clonorchis sinensis:** Known as the Chinese Liver Fluke, it causes biliary tract infections and is a major risk factor for **cholangiocarcinoma**, not cystic lesions. * **B. Wuchereria bancrofti:** A nematode responsible for **Lymphatic Filariasis (Elephantiasis)**, transmitted by the *Culex* mosquito. It affects the lymphatic system, not visceral organs via cysts. * **C. Ascaris lumbricoides:** The Giant Roundworm. It causes intestinal obstruction or Loeffler’s syndrome (pneumonitis) but does not form hydatid cysts. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** Ultrasound shows a "Water-lily sign" (collapsed germinal membrane). CT may show "Eggshell calcification" of the cyst wall. * **Casoni Test:** An immediate hypersensitivity skin test (now largely replaced by serology/ELISA). * **Management:** **PAIR** technique (Puncture, Aspiration, Injection of scolicidal agent like hypertonic saline, Re-aspiration). * **Complication:** Spontaneous or surgical rupture of the cyst can lead to a fatal **Anaphylactic reaction** due to the highly antigenic hydatid fluid.
Practice by Chapter
Classification of Parasites
Practice Questions
Intestinal Protozoa
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Blood and Tissue Protozoa
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Malaria Parasites
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Leishmaniasis
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Intestinal Helminths: Nematodes
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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
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