Parasitology — MCQs
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The adult worm of Echinococcus granulosus is commonly found in which of the following animals?
Which of the following acts as a reservoir for Toxoplasma gondii?
A 35-year-old man who recently traveled to a tropical country develops chronic, severe dysentery. Colonoscopy demonstrates ulceration of the cecum, and a cecal biopsy reveals 15-to-40 micron amoebae with ingested erythrocytes and small nuclei with distinctive tiny central karyosomes. Which of the following organisms is the most likely culprit?
What is the shortest incubation period in malaria?
Which of the following infections is not sexually transmitted?
Which parasite commonly causes lung infestation?
What is the causative agent of malaria?
Which of the following is the commonest cause of malaria in the world?
Which of the following diseases is NOT transmitted by fleas?
Which of the following parasites can be found in ocular muscles?
Parasitology Indian Medical PG Practice Questions and MCQs
Question 731: The adult worm of Echinococcus granulosus is commonly found in which of the following animals?
- A. Dog (Correct Answer)
- B. Cat
- C. Sheep
- D. Pig
Explanation: **Explanation:** The correct answer is **Dog (Option A)**. *Echinococcus granulosus*, also known as the "Dog Tapeworm," causes cystic echinococcosis (Hydatid disease). To understand the host distribution, it is essential to distinguish between the definitive and intermediate hosts: 1. **Definitive Host (Dog):** The **adult worm** resides in the small intestine of canines (dogs, wolves, foxes). Dogs acquire the infection by ingesting the larval form (hydatid cysts) found in the organs of intermediate hosts. 2. **Intermediate Host (Sheep/Cattle):** These animals harbor the **larval stage** (hydatid cyst). Humans act as **accidental intermediate hosts** (dead-end hosts) by ingesting eggs shed in dog feces. **Analysis of Incorrect Options:** * **B. Cat:** Cats are not natural hosts for *E. granulosus*. While they can harbor other parasites, they do not play a role in the transmission cycle of this specific tapeworm. * **C. Sheep:** Sheep are the most common **intermediate hosts**. They harbor the hydatid cyst (larval stage), not the adult worm. * **D. Pig:** Similar to sheep, pigs serve as intermediate hosts for certain strains of *Echinococcus*, harboring the larval stage. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Stage for Humans:** Embryonated eggs (found in dog feces). * **Diagnostic Feature:** "Hydatid sand" (brood capsules and protoscolices) found within the cyst fluid. * **Radiology:** "Water lily sign" (collapsed germinal membrane) on USG/CT. * **Casoni’s Test:** An immediate hypersensitivity skin test (now largely replaced by serology/ELISA). * **Treatment Precaution:** During surgery, extreme care is taken to avoid cyst rupture, which can lead to life-threatening **anaphylaxis**. PAIR (Puncture, Aspiration, Injection, Re-aspiration) is a minimally invasive treatment option.
Question 732: Which of the following acts as a reservoir for Toxoplasma gondii?
- A. Toxoplasma gondii (Correct Answer)
- B. Rabies
- C. Streptocerca infection
- D. Plague
Explanation: **Explanation:** The question identifies **Toxoplasma gondii** as its own reservoir, which refers to the biological cycle where the parasite persists in various hosts. *Toxoplasma gondii* is an obligate intracellular protozoan. Its definitive hosts are members of the **Felidae family (cats)**, where sexual reproduction occurs. However, it has a remarkably broad host range, using virtually any warm-blooded animal (including humans, rodents, and livestock) as intermediate hosts where it maintains a chronic presence in the form of tissue cysts. **Analysis of Options:** * **Toxoplasma gondii (Correct):** In the context of this question, the organism itself represents the infection cycle. The reservoir system involves the feline-environment-prey cycle. * **Rabies (Incorrect):** Rabies is a viral zoonosis. Its primary reservoirs are wild animals such as bats, raccoons, skunks, and foxes (and domestic dogs in developing regions). * **Streptocerca infection (Incorrect):** Caused by *Mansonella streptocerca*, this filarial nematode is transmitted by *Culicoides* biting midges. The primary reservoir is humans (and occasionally monkeys). * **Plague (Incorrect):** Caused by *Yersinia pestis*, the primary reservoirs are wild rodents (e.g., rats, ground squirrels). **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Ingestion of oocysts (cat feces), bradyzoites (undercooked meat), or transplacental transfer. * **Congenital Toxoplasmosis Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Diagnosis:** Sabin-Feldman Dye Test (Gold Standard), though rarely used now; IgM/IgG ELISA is standard. * **Drug of Choice:** Pyrimethamine + Sulfadiazine. * **AIDS Patients:** Most common cause of CNS mass lesions (Ring-enhancing lesions on CT/MRI).
Question 733: A 35-year-old man who recently traveled to a tropical country develops chronic, severe dysentery. Colonoscopy demonstrates ulceration of the cecum, and a cecal biopsy reveals 15-to-40 micron amoebae with ingested erythrocytes and small nuclei with distinctive tiny central karyosomes. Which of the following organisms is the most likely culprit?
- A. Acanthamoeba sp
- B. Balantidium coli
- C. Entamoeba histolytica (Correct Answer)
- D. Giardia lamblia
Explanation: ### Explanation **1. Why Entamoeba histolytica is Correct:** The clinical presentation of chronic dysentery combined with specific histopathological findings is pathognomonic for *Entamoeba histolytica*. * **Ingested Erythrocytes (Erythrophagocytosis):** This is the most definitive diagnostic feature used to distinguish the pathogenic *E. histolytica* from the morphologically identical but non-pathogenic *E. dispar*. * **Nuclear Morphology:** The description of a small, central karyosome (nucleolus) and fine, peripheral chromatin is characteristic of the *Entamoeba* genus. * **Pathology:** *E. histolytica* typically causes "flask-shaped" ulcers in the cecum and colon by secreting proteolytic enzymes (histolysins) that invade the submucosa. **2. Why the Other Options are Incorrect:** * **Acanthamoeba sp:** Primarily causes Granulomatous Amoebic Encephalitis (GAE) or keratitis (associated with contact lens use). It does not cause dysentery. * **Balantidium coli:** While it causes similar large-bowel ulceration and dysentery, it is a much larger ciliated protozoan (50–200 µm) with a characteristic kidney-shaped macronucleus. It does not ingest RBCs. * **Giardia lamblia:** This parasite affects the duodenum and jejunum (small intestine), leading to malabsorption and foul-smelling, fatty stools (steatorrhea), not bloody dysentery or colonic ulcers. **3. NEET-PG High-Yield Pearls:** * **Trophozoite vs. Cyst:** The trophozoite is the invasive form (found in dysenteric stools); the quadrinucleated cyst is the infective form (found in chronic cases/carriers). * **Commonest Site:** The cecum and ascending colon are the most common sites for intestinal amoebiasis. * **Extra-intestinal Complication:** The most common is an **Amoebic Liver Abscess**, typically presenting with "anchovy sauce" pus. * **Treatment:** Metronidazole or Tinidazole (luminal agents like Paromomycin are added to eradicate cysts).
Question 734: What is the shortest incubation period in malaria?
- A. Plasmodium vivax
- B. Plasmodium falciparum (Correct Answer)
- C. Plasmodium malariae
- D. Plasmodium ovale
Explanation: ### Explanation The **incubation period** in malaria refers to the time interval between the bite of an infected female *Anopheles* mosquito and the onset of clinical symptoms (usually fever). This period is primarily determined by the duration of the **pre-erythrocytic (exo-erythrocytic) schizogony** in the liver. **Why Plasmodium falciparum is correct:** *Plasmodium falciparum* has the shortest pre-erythrocytic cycle, lasting approximately **5–7 days**, leading to an average incubation period of **9–14 days** (range can be as short as 7 days). Because it lacks a dormant hypnozoite stage and replicates rapidly, it manifests clinically faster than other species. **Analysis of Incorrect Options:** * **P. vivax:** The incubation period is typically **12–17 days**. While the liver stage lasts about 8 days, the onset of symptoms is slightly slower than *P. falciparum*. It can also cause relapses due to dormant **hypnozoites**. * **P. ovale:** Similar to *P. vivax*, it has an incubation period of **16–18 days** and possesses a hypnozoite stage. * **P. malariae:** This species has the **longest** incubation period, typically ranging from **18–40 days**. Its pre-erythrocytic stage lasts about 15 days, and it has a slower erythrocytic cycle (72 hours). **NEET-PG High-Yield Pearls:** 1. **Shortest Incubation Period:** *P. falciparum* (9–14 days). 2. **Longest Incubation Period:** *P. malariae* (18–40 days). 3. **Pre-erythrocytic Cycle Duration:** *P. falciparum* (6 days) < *P. vivax* (8 days) < *P. ovale* (9 days) < *P. malariae* (15 days). 4. **Relapse vs. Recrudescence:** Relapse (liver stage) occurs in *P. vivax* and *P. ovale*. Recrudescence (blood stage survival) is characteristic of *P. falciparum* and *P. malariae*.
Question 735: Which of the following infections is not sexually transmitted?
- A. Echinococcus (Correct Answer)
- B. Chlamydia
- C. Treponema pallidum
- D. Neisseria gonorrhoeae
Explanation: ### Explanation The correct answer is **A. Echinococcus**. **1. Why Echinococcus is the correct answer:** *Echinococcus granulosus* is a cestode (tapeworm) that causes **Hydatid disease**. Its transmission is **fecal-oral**, primarily through the ingestion of food or water contaminated with eggs shed in the feces of definitive hosts (dogs). It is not a sexually transmitted infection (STI). The lifecycle involves dogs (definitive host) and sheep/cattle (intermediate hosts), with humans acting as accidental intermediate hosts. **2. Why the other options are incorrect:** * **B. Chlamydia trachomatis:** This is the most common bacterial STI worldwide. Serotypes D-K cause non-gonococcal urethritis, cervicitis, and PID, while serotypes L1-L3 cause Lymphogranuloma Venereum (LGV). * **C. Treponema pallidum:** This spirochete is the causative agent of **Syphilis**. It is primarily transmitted through direct contact with an infectious lesion (chancre) during sexual intercourse. * **D. Neisseria gonorrhoeae:** A Gram-negative diplococcus that causes **Gonorrhea**. It is a classic STI that infects the mucous membranes of the reproductive tract, mouth, and anus. **3. NEET-PG High-Yield Pearls:** * **Parasitic STIs:** While *Echinococcus* is not an STI, remember that **_Trichomonas vaginalis_** (a protozoan) is a major parasitic STI. Occasionally, *Entamoeba histolytica* and *Giardia* can be transmitted sexually via the fecal-oral route (common in MSM populations). * **Hydatid Cyst:** Look for "Egg-shell calcification" on X-ray and "Water lily sign" or "Camelot sign" on USG/CT. * **Treatment of choice for Echinococcus:** Surgical excision (PAIR technique) combined with **Albendazole**.
Question 736: Which parasite commonly causes lung infestation?
- A. Hymenolepis nana
- B. Paragonimus westermanii (Correct Answer)
- C. Taenia saginata
- D. Echinococcus granulosus
Explanation: **Explanation:** **Paragonimus westermani** (the Oriental Lung Fluke) is the correct answer because it is the primary trematode specifically adapted to inhabit the lung parenchyma. Humans acquire the infection by consuming raw or undercooked crustaceans (crabs/crayfish) containing metacercariae. Once ingested, the larvae penetrate the intestinal wall, migrate through the diaphragm, and mature into adult worms within fibrous cysts in the lungs. This leads to **endemic hemoptysis**, often mimicking pulmonary tuberculosis. **Analysis of Incorrect Options:** * **Hymenolepis nana (Dwarf Tapeworm):** This is the most common intestinal helminth. Its entire life cycle occurs within the gastrointestinal tract; it does not have a migratory lung phase. * **Taenia saginata (Beef Tapeworm):** This parasite resides in the small intestine of humans. While the larvae (Cysticercus bovis) are found in the muscles of cattle, they do not typically cause lung infestation in humans. * **Echinococcus granulosus:** While this parasite can cause **Hydatid cysts** in the lungs (the second most common site after the liver), it is not primarily a "lung fluke." *Paragonimus* is the more "common" and definitive answer when discussing primary lung infestation in a parasitology context. **NEET-PG High-Yield Pearls:** * **Intermediate Hosts:** 1st: Snail (*Semisulcospira*); 2nd: Crustaceans (Crab/Crayfish). * **Diagnosis:** Identification of golden-brown, operculated eggs in **sputum** or feces. * **Radiology:** May show "ring-shadow" opacities or "cotton-wool" appearances. * **Drug of Choice:** Praziquantel.
Question 737: What is the causative agent of malaria?
- A. Protozoa (Correct Answer)
- B. Mosquito
- C. Bacteria
- D. Virus
Explanation: **Explanation:** The causative agent of malaria is a unicellular eukaryotic organism belonging to the genus ***Plasmodium***. In medical microbiology, *Plasmodium* species (such as *P. falciparum, P. vivax, P. ovale, P. malariae,* and *P. knowlesi*) are classified as **Protozoa** under the Phylum Apicomplexa. These parasites infect the host's liver cells and erythrocytes to complete their asexual life cycle. **Analysis of Options:** * **A. Protozoa (Correct):** Malaria is caused by protozoan parasites. They are characterized by complex life cycles involving an intermediate host (humans) and a definitive host (mosquitoes). * **B. Mosquito (Incorrect):** The female *Anopheles* mosquito is the **vector**, not the causative agent. It transmits the infective stage (sporozoites) from one human to another. * **C. Bacteria (Incorrect):** Malaria does not involve prokaryotic organisms. Bacterial infections are treated with antibiotics, whereas malaria requires antiprotozoal (antimalarial) drugs. * **D. Virus (Incorrect):** Viruses are acellular obligate intracellular parasites. While some tropical fevers like Dengue or Zika are viral, malaria is parasitic. **NEET-PG High-Yield Pearls:** * **Definitive Host:** Female *Anopheles* mosquito (where the sexual cycle/sporogony occurs). * **Intermediate Host:** Humans (where the asexual cycle/schizogony occurs). * **Infective Form to Humans:** Sporozoites (injected via mosquito bite). * **Infective Form to Mosquito:** Gametocytes (ingested during a blood meal). * **Relapse:** Seen in *P. vivax* and *P. ovale* due to dormant liver stages called **hypnozoites**. * **Gold Standard Diagnosis:** Peripheral blood smear (thick for detection, thin for species identification).
Question 738: Which of the following is the commonest cause of malaria in the world?
- A. P. vivax (Correct Answer)
- B. P. ovale
- C. P. falciparum
- D. P. malariae
Explanation: **Explanation:** The correct answer is **P. vivax**. **1. Why P. vivax is correct:** While *Plasmodium falciparum* is the leading cause of malaria-related mortality (especially in Africa), **Plasmodium vivax** is the most **geographically widespread** and commonest cause of malaria globally. It has a broader distribution because it can develop in the *Anopheles* mosquito at lower temperatures and possesses a dormant liver stage (**hypnozoite**), allowing it to survive in temperate climates and cause relapses. In the context of the Indian subcontinent and global prevalence outside of sub-Saharan Africa, *P. vivax* remains the predominant species. **2. Why other options are incorrect:** * **P. falciparum:** It is the most **virulent** species and the leading cause of malaria in Africa. While it accounts for the majority of malaria deaths worldwide, its global geographical footprint is slightly more restricted to tropical regions compared to *P. vivax*. * **P. ovale:** This is the rarest of the four major species, primarily confined to West Africa and some islands in the Western Pacific. * **P. malariae:** This species has a wide but patchy distribution. It is known for causing "quartan malaria" and long-term asymptomatic infections, but it is significantly less common than *P. vivax* or *P. falciparum*. **3. NEET-PG High-Yield Pearls:** * **Relapse vs. Recrudescence:** *P. vivax* and *P. ovale* cause **relapse** (due to hypnozoites in the liver). *P. falciparum* and *P. malariae* cause **recrudescence** (due to persistent sub-clinical blood stages). * **Duffy Antigen:** Individuals lacking the Duffy blood group antigen are resistant to *P. vivax* infection. * **Schüffner’s dots:** Characteristically seen in RBCs infected with *P. vivax* and *P. ovale*. * **Incubation Period:** *P. falciparum* has the shortest (12 days), while *P. malariae* has the longest (28 days).
Question 739: Which of the following diseases is NOT transmitted by fleas?
- A. Plague
- B. Endemic typhus
- C. Chiggerosis
- D. Trench fever (Correct Answer)
Explanation: **Explanation:** The correct answer is **Trench fever** because it is transmitted by the **human body louse** (*Pediculus humanus corporis*), not by fleas. It is caused by the bacterium *Bartonella quintana*. **Breakdown of Options:** * **Trench fever (Correct):** This is a louse-borne disease historically significant during WWI. The body louse also transmits Epidemic typhus (*Rickettsia prowazekii*) and Louse-borne relapsing fever (*Borrelia recurrentis*). * **Plague:** Transmitted by the **rat flea** (*Xenopsylla cheopis*). This is the most famous flea-borne disease, caused by *Yersinia pestis*. * **Endemic typhus:** Also known as Murine typhus, it is caused by *Rickettsia typhi* and is transmitted to humans via the feces of infected **rat fleas**. * **Chiggerosis (Tungiasis):** Caused by the direct infestation of the skin by the **sand flea** (*Tunga penetrans*). Note: Do not confuse this with "Chiggers" (larval mites) which cause Scrub typhus. **High-Yield Clinical Pearls for NEET-PG:** * **Vector Mnemonic:** Remember the "Three Louse-borne diseases": **Epidemic** Typhus, **Trench** Fever, and **Relapsing** Fever (**E**very **T**errible **R**at). * **Xenopsylla cheopis:** The most efficient vector for Plague; it undergoes "blocking" where the bacteria multiply in the flea's proventriculus, forcing it to bite humans repeatedly. * **Bartonella quintana:** Unique among Rickettsial-like organisms because it can be grown on cell-free culture media (blood agar).
Question 740: Which of the following parasites can be found in ocular muscles?
- A. Trichinella (Correct Answer)
- B. Ascaris
- C. Enterobius
- D. None of the above
Explanation: **Explanation:** The correct answer is **Trichinella spiralis**. This nematode is the causative agent of **Trichinellosis**, a disease typically acquired by consuming undercooked meat (especially pork) containing encysted larvae. **Why Trichinella is correct:** After ingestion, larvae mature in the small intestine, and the female releases newborn larvae into the bloodstream. These larvae have a high tropism for **striated muscles** with high metabolic activity and rich blood supply. The **extraocular muscles** are among the most frequently involved sites, followed by the diaphragm, tongue, and intercostal muscles. The larvae encyst within these muscles, leading to the classic clinical triad of **periorbital edema, myalgia, and eosinophilia.** **Why the other options are incorrect:** * **Ascaris lumbricoides:** This is an intestinal nematode. While its larvae undergo a heart-lung migration (Loeffler’s syndrome), they do not encyst in skeletal or ocular muscles. * **Enterobius vermicularis (Pinworm):** This parasite resides in the cecum and appendix. Its primary clinical manifestation is perianal pruritus; it does not involve muscle tissue. **NEET-PG High-Yield Pearls:** * **Diagnostic Feature:** Muscle biopsy showing **encysted larvae** (coiled larvae) is the gold standard. * **Laboratory Finding:** Marked **Eosinophilia** and elevated **Creatine Kinase (CK)** levels due to muscle destruction. * **Drug of Choice:** Albendazole or Mebendazole (effective against adult worms; steroids are added for severe systemic symptoms caused by larval encystment). * **Splinter hemorrhages:** Often seen under the fingernails in Trichinellosis, mimicking infective endocarditis.
Practice by Chapter
Classification of Parasites
Practice Questions
Intestinal Protozoa
Practice Questions
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
Practice Questions
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