Parasitology — MCQs
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Trussell and Johnson's medium is used for the cultivation of which organism?
What is the intermediate host where the larval form of Taenia solium is typically found?
A veterinarian presents with a chief complaint of thin, watery, non-bloody diarrhea for the past two weeks. He appears fatigued and mildly dehydrated. Stool examination is negative for leukocytes and culture for bacterial pathogens is negative. Acid-fast stain of the stool demonstrates oocysts that are 5-7 microns in diameter. Where does the sexual phase of this organism's life cycle occur?
Which of the following infections predisposes to cancer?
Multilocular hydatid cysts are caused by which organism?
A patient with HIV presents with diarrhea and acid-fast bacilli (AFB) positive stool. What is the most likely causative organism?
Eggs seen in sputum and stools belong to which parasite?
Lyme disease is transmitted by which of the following vectors, except?
A male patient in a tropical environment has eosinophilia during acute inflammatory episodes of his illness. Transmission of human parasites may occur via ingestion of contaminated food, water, snails, a variety of insects, and possibly even through pets or rat ectoparasites. Which of the following parasitic infections requires a mosquito for transmission?
Cyclops are intermediate hosts for which of the following?
Parasitology Indian Medical PG Practice Questions and MCQs
Question 71: Trussell and Johnson's medium is used for the cultivation of which organism?
- A. Giardia
- B. Leishmania
- C. Trichomonas (Correct Answer)
- D. Chilomastix
Explanation: **Explanation:** **Trichomonas vaginalis** is the correct answer. **Trussell and Johnson’s medium** (also known as Cysteine-Peptone-Liver infusion-Maltose or **CPLM medium**) is a specialized liquid medium designed for the cultivation of *Trichomonas vaginalis*. It contains essential nutrients like liver infusion and maltose, often supplemented with antibiotics (penicillin/streptomycin) to inhibit bacterial overgrowth. While diagnosis is usually made via wet mount (showing jerky motility) or Pap smear, culture remains the "gold standard" for detection, especially in asymptomatic cases. **Analysis of Incorrect Options:** * **Giardia:** Cultivated using **Diamond’s medium** (TYI-S-33), though diagnosis is primarily clinical via stool microscopy for cysts/trophozoites or ELISA. * **Leishmania:** Cultivated using **NNN (Novy-MacNeal-Nicolle) medium**, which is a blood agar-based biphasic medium. It shows the promastigote stage. * **Chilomastix:** This is a non-pathogenic commensal flagellate. While it can grow in general enteric media like Boeck and Drbohlav’s, it is rarely cultivated in clinical practice. **High-Yield Clinical Pearls for NEET-PG:** * **Other Media for Trichomonas:** Feinberg-Whittington medium and Diamond’s medium. * **Clinical Presentation:** Causes "Strawberry Cervix" (punctate hemorrhages) and a malodorous, frothy, yellowish-green vaginal discharge. * **Vaginal pH:** Unlike Candidiasis (pH <4.5), Trichomoniasis typically presents with a **pH >4.5**. * **Treatment:** Metronidazole is the drug of choice; **simultaneous treatment of the partner** is mandatory to prevent "ping-pong" reinfection.
Question 72: What is the intermediate host where the larval form of Taenia solium is typically found?
- A. Pig (Correct Answer)
- B. Cattle
- C. Dog
- D. Cat
Explanation: **Explanation:** The life cycle of **_Taenia solium_ (Pork Tapeworm)** involves two hosts. Humans serve as the **definitive host**, harboring the adult tapeworm in the small intestine. **Pigs** serve as the **intermediate host**, where the ingested eggs hatch into oncospheres, penetrate the intestinal wall, and migrate to the muscles to develop into the larval stage, known as **Cysticercus cellulosae**. Humans become infected by consuming undercooked pork containing these larvae. **Analysis of Options:** * **A. Pig (Correct):** The natural intermediate host for _T. solium_. Note: Humans can also act as accidental intermediate hosts if they ingest eggs (via feco-oral route), leading to **Cysticercosis**. * **B. Cattle:** This is the intermediate host for **_Taenia saginata_ (Beef Tapeworm)**. _T. saginata_ does not cause cysticercosis in humans. * **C. Dog:** The definitive host for **_Echinococcus granulosus_** (Hydatid disease). Humans and sheep act as intermediate hosts here. * **D. Cat:** Primarily associated with **_Toxoplasma gondii_** (definitive host) or _Opisthorchis_ species, but not involved in the _Taenia_ life cycle. **High-Yield Clinical Pearls for NEET-PG:** * **Neurocysticercosis (NCC):** The most common cause of adult-onset seizures worldwide, caused by the larval stage of _T. solium_ in the brain. * **Diagnosis:** Stool microscopy for eggs/proglottids (Taeniasis) or MRI/CT showing "hole-with-dot" appearance (NCC). * **Treatment:** Praziquantel for intestinal infection; Albendazole + Steroids for NCC. * **Key Distinction:** In _T. solium_, the gravid uterus has **7–13 lateral branches**, whereas _T. saginata_ has **15–30**.
Question 73: A veterinarian presents with a chief complaint of thin, watery, non-bloody diarrhea for the past two weeks. He appears fatigued and mildly dehydrated. Stool examination is negative for leukocytes and culture for bacterial pathogens is negative. Acid-fast stain of the stool demonstrates oocysts that are 5-7 microns in diameter. Where does the sexual phase of this organism's life cycle occur?
- A. Attached to the colonic mucosa of swine
- B. Extracellularly in the small intestine of muskrats and beavers
- C. In the brush border of the intestinal epithelium of humans (Correct Answer)
- D. Intracellularly in the intestinal mucosa of felines
Explanation: **Explanation:** The clinical presentation of chronic watery diarrhea in a veterinarian, combined with the finding of **acid-fast oocysts (5–7 µm)** in the stool, is diagnostic of ***Cryptosporidium parvum***. **1. Why the Correct Answer is Right:** *Cryptosporidium* is unique among coccidian parasites because it occupies an **intracellular but extracytoplasmic** niche. It resides within the **brush border of the intestinal epithelium** (primarily the small intestine). Both the asexual (schizogony) and **sexual (gametogony)** phases of its life cycle occur in this specific location within the host. This leads to villous atrophy and malabsorptive diarrhea. **2. Analysis of Incorrect Options:** * **Option A:** Swine are hosts for *Balantidium coli*, which causes dysentery and inhabits the large intestine, but it is a ciliate, not an acid-fast oocyst. * **Option B:** Muskrats and beavers are reservoirs for *Giardia lamblia*. While *Giardia* is extracellular, it is a flagellate and does not stain acid-fast. * **Option C:** Felines (cats) are the **definitive hosts** for *Toxoplasma gondii*. The sexual phase of *Toxoplasma* occurs in the feline gut, but *Toxoplasma* does not cause primary diarrheal illness in humans; it presents as systemic infection. **3. High-Yield Clinical Pearls for NEET-PG:** * **Stain:** Modified Kinyoun’s Acid-Fast stain is the gold standard. * **Size Matters:** *Cryptosporidium* (5–7 µm) is smaller than *Cyclospora* (8–10 µm) and *Isospora* (25–30 µm). * **Immunocompromised Patients:** In HIV/AIDS (CD4 <100), it causes severe, life-threatening cholera-like diarrhea. * **Transmission:** Highly resistant to chlorination; common in swimming pools and among animal handlers (veterinarians). * **Treatment:** **Nitazoxanide** is the drug of choice in immunocompetent patients.
Question 74: Which of the following infections predisposes to cancer?
- A. Schistosomiasis (Correct Answer)
- B. Taenia solium
- C. Taenia saginata
- D. Strongyloides
Explanation: **Explanation:** The correct answer is **Schistosomiasis (Option A)**. Specifically, chronic infection with ***Schistosoma haematobium*** (the urinary blood fluke) is a well-established risk factor for **Squamous Cell Carcinoma (SCC) of the urinary bladder**. **Why it is correct:** The pathogenesis involves the deposition of parasite eggs in the bladder wall, leading to chronic inflammation, oxidative stress, and tissue repair. Over years, this results in squamous metaplasia of the transitional epithelium, eventually progressing to SCC. This is a high-yield distinction, as most non-parasitic bladder cancers in the West are Transitional Cell Carcinomas (TCC). **Why the other options are incorrect:** * **Taenia solium (B):** Causes Taeniasis (intestinal) and Cysticercosis (tissue). While it causes significant morbidity (Neurocysticercosis), it is not associated with oncogenesis. * **Taenia saginata (C):** Causes intestinal Taeniasis; it is generally benign and lacks any association with malignancy. * **Strongyloides stercoralis (D):** Known for the "autoinfection" cycle and hyperinfection syndrome in immunocompromised patients, but it does not predispose to cancer. **High-Yield NEET-PG Clinical Pearls:** 1. **Other Oncogenic Parasites:** * *Clonorchis sinensis* and *Opisthorchis viverrini* (Liver flukes) are strongly associated with **Cholangiocarcinoma** (bile duct cancer). 2. **S. haematobium Key Features:** Terminal spine on eggs; causes painless terminal hematuria. 3. **Drug of Choice:** Praziquantel is the gold standard treatment for all Schistosoma species.
Question 75: Multilocular hydatid cysts are caused by which organism?
- A. E. granulosus
- B. E. multilocularis (Correct Answer)
- C. Clonorchis sinensis
- D. Paragonimus westermani
Explanation: ### Explanation **Correct Answer: B. Echinococcus multilocularis** **1. Why it is correct:** *Echinococcus multilocularis* is the causative agent of **Alveolar Hydatid Disease**. Unlike *E. granulosus*, which forms a single, fluid-filled unilocular cyst with a thick wall, *E. multilocularis* produces a "multilocular" or alveolar structure. This cyst lacks a limiting laminated membrane, allowing the larvae to bud externally. This results in an invasive, honeycomb-like mass of small vesicles that infiltrates host tissue (primarily the liver) like a malignant tumor, often leading to metastasis. **2. Why the other options are incorrect:** * **A. E. granulosus:** This is the most common cause of hydatid disease but produces **unilocular** cysts. These are well-circumscribed, slow-growing, and characterized by three distinct layers (pericyst, ectocyst, and endocyst). * **C. Clonorchis sinensis:** Known as the Chinese Liver Fluke, it resides in the bile ducts and causes clonorchiasis, which is associated with cholangiocarcinoma, not hydatid cysts. * **D. Paragonimus westermani:** Known as the Oriental Lung Fluke, it primarily causes pulmonary infections resembling tuberculosis, characterized by "rusty sputum" and cavitary lesions in the lungs. **3. NEET-PG High-Yield Pearls:** * **Definitive Host:** Foxes (primarily) and dogs for *E. multilocularis*; Dogs for *E. granulosus*. * **Intermediate Host:** Rodents for *E. multilocularis*; Sheep/Cattle (and accidentally Humans) for *E. granulosus*. * **Radiology:** *E. granulosus* shows "Water-lily sign" or "Camelot sign" (detached endocyst). *E. multilocularis* presents as an ill-defined infiltrative mass with "hailstorm" calcifications. * **Treatment:** Surgical resection is difficult for *E. multilocularis* due to its invasive nature; long-term Albendazole is usually required. For *E. granulosus*, the **PAIR** (Puncture, Aspiration, Injection, Re-aspiration) technique is a classic board-favorite.
Question 76: A patient with HIV presents with diarrhea and acid-fast bacilli (AFB) positive stool. What is the most likely causative organism?
- A. Mycobacterium avium intracellulare (Correct Answer)
- B. Mycobacterium tuberculosis
- C. Mycobacterium leprae
- D. Mycoplasma
Explanation: **Explanation:** The correct answer is **Mycobacterium avium intracellulare (MAC)**. In the context of HIV/AIDS, particularly when the CD4 count falls below 50 cells/mm³, **Disseminated MAC infection** is a common opportunistic infection. MAC is an **Atypical Mycobacterium** (Non-Tuberculous Mycobacterium) that is characterized by being **Acid-Fast Positive**. Clinically, it presents with systemic symptoms like fever, night sweats, weight loss, and significant gastrointestinal involvement leading to **chronic diarrhea** and malabsorption. Finding AFB in the stool of an immunocompromised patient is a classic diagnostic clue for MAC. **Analysis of Incorrect Options:** * **B. Mycobacterium tuberculosis:** While it is the most common opportunistic infection in HIV patients and is Acid-Fast, it primarily involves the lungs or lymph nodes. While abdominal TB exists (ileocecal), it typically presents with pain or obstruction rather than the profuse diarrhea associated with MAC in advanced AIDS. * **C. Mycobacterium leprae:** This is the causative agent of Leprosy, affecting the skin and peripheral nerves. It is not associated with HIV-related diarrhea or stool findings. * **D. Mycoplasma:** These are the smallest free-living organisms and **lack a cell wall**. Because they lack a cell wall, they do not take up Gram stain or Acid-Fast stain (AFB negative). **NEET-PG High-Yield Pearls:** * **Stain:** MAC is visualized using the **Modified Ziehl-Neelsen stain**. * **Prophylaxis:** In HIV patients with CD4 <50, Azithromycin or Clarithromycin is used for MAC prophylaxis. * **Differential Diagnosis:** Other AFB-positive organisms in HIV stool include *Cryptosporidium parvum*, *Isospora belli*, and *Cyclospora* (these are protozoa, not bacteria). * **Culture:** MAC grows on Lowenstein-Jensen (LJ) medium but much more slowly than *M. tuberculosis*.
Question 77: Eggs seen in sputum and stools belong to which parasite?
- A. Paragonimus (Correct Answer)
- B. Fasciola
- C. Clonorchis
- D. Pneumocystis carinii
Explanation: **Explanation:** The correct answer is **Paragonimus westermani** (the lung fluke). This parasite primarily inhabits the lungs of humans. The adult flukes reside within fibrous cysts in the pulmonary parenchyma. Eggs are released into the bronchioles and are subsequently coughed up in the **sputum**. However, because patients often swallow their sputum, these eggs pass through the gastrointestinal tract and are frequently detected in the **stools** as well. **Analysis of Options:** * **Fasciola hepatica (Liver fluke):** Resides in the bile ducts. Eggs are excreted in feces but are never found in sputum as they do not involve the respiratory tract. * **Clonorchis sinensis (Chinese liver fluke):** Also inhabits the biliary tree. Diagnosis is made by detecting eggs in stool or biliary aspirates, not sputum. * **Pneumocystis carinii (now *P. jirovecii*):** This is a fungus (formerly classified as a protozoan). It causes pneumonia and can be found in sputum/BAL, but it **does not produce eggs**; it exists as cysts and trophozoites and is not found in stool for diagnostic purposes. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *Paragonimus* eggs are operculated, golden-brown, and thick-shelled. * **Transmission:** Ingestion of undercooked **crabs or crayfish** (Second intermediate host). * **Clinical Presentation:** Often mimics Pulmonary Tuberculosis (chronic cough, hemoptysis, and night sweats), a condition termed "Endemic Hemoptysis." * **Radiology:** May show "ring shadows" or "cotton-wool" opacities in the lungs. * **Treatment:** Praziquantel is the drug of choice.
Question 78: Lyme disease is transmitted by which of the following vectors, except?
- A. Ixodes pacificus
- B. Ixodes scapularis
- C. Ixodes damminii (Correct Answer)
- D. None of the above
Explanation: **Explanation:** The correct answer is **C. Ixodes damminii**. This question is a classic "nomenclature trap" often seen in NEET-PG. **Why Option C is the correct answer:** *Ixodes damminii* is no longer considered a separate species. In the early 1990s, taxonomists determined that *Ixodes damminii* (previously thought to be the primary vector in the Northeastern US) is actually the same species as **Ixodes scapularis**. Therefore, the name *I. damminii* has been invalidated and replaced by *I. scapularis*. In the context of "except" questions, this option is technically the "odd one out" because it is a defunct taxonomic name rather than a currently recognized distinct vector. **Analysis of other options:** * **Ixodes scapularis (Option B):** Also known as the Black-legged tick or Deer tick, it is the primary vector for Lyme disease (*Borrelia burgdorferi*) in the Northeastern, Mid-Atlantic, and North-Central United States. * **Ixodes pacificus (Option A):** Known as the Western black-legged tick, it is the principal vector for Lyme disease on the Pacific Coast of the United States. **High-Yield Clinical Pearls for NEET-PG:** 1. **Causative Agent:** *Borrelia burgdorferi* (a spirochete). 2. **Reservoir:** White-footed mouse (*Peromyscus leucopus*). The deer is the host for the adult tick but not the reservoir for the bacteria. 3. **Clinical Stages:** * **Stage 1:** Erythema Chronicum Migrans (Bull’s eye rash). * **Stage 2:** Early disseminated (Bilateral Bell’s palsy, AV block). * **Stage 3:** Chronic (Lyme arthritis, Encephalopathy). 4. **Drug of Choice:** Doxycycline (Amoxicillin in children <8 years and pregnant women). 5. **European Vector:** In Europe and Asia, the primary vector is *Ixodes ricinus*.
Question 79: A male patient in a tropical environment has eosinophilia during acute inflammatory episodes of his illness. Transmission of human parasites may occur via ingestion of contaminated food, water, snails, a variety of insects, and possibly even through pets or rat ectoparasites. Which of the following parasitic infections requires a mosquito for transmission?
- A. Babesiosis
- B. Bancroftian filariasis (Correct Answer)
- C. Dog tapeworm
- D. Guinea worm
Explanation: **Explanation:** The correct answer is **Bancroftian filariasis**. This condition is caused by the nematode *Wuchereria bancrofti*. In tropical regions, it is primarily transmitted by the bite of an infected **Culex mosquito** (specifically *Culex quinquefasciatus*). The clinical presentation of eosinophilia during acute inflammatory episodes (adenolymphangitis) is a hallmark of lymphatic filariasis, as the immune system reacts to the presence of adult worms and microfilariae. **Analysis of Incorrect Options:** * **Babesiosis:** This is a malaria-like protozoan infection transmitted by the **Ixodes tick** (the same vector for Lyme disease). It is not mosquito-borne. * **Dog tapeworm (*Echinococcus granulosus*):** Transmission occurs via the **fecal-oral route** through the ingestion of eggs from food or water contaminated by dog feces. * **Guinea worm (*Dracunculus medinensis*):** Transmission occurs by **ingesting contaminated water** containing infected **Cyclops** (water fleas/crustaceans), which act as the intermediate host. **NEET-PG High-Yield Pearls:** * **Vector for Filariasis:** While *Culex* is the main vector for *W. bancrofti*, *Mansonia* mosquitoes transmit *Brugia malayi*. * **Diagnosis:** The gold standard is the detection of microfilariae in a **peripheral blood smear** collected at night (**Nocturnal Periodicity**, typically 10 PM – 2 AM). * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by paroxysmal cough, wheezing, and massive eosinophilia (>3000/µL). * **Drug of Choice:** Diethylcarbamazine (DEC) is the mainstay of treatment.
Question 80: Cyclops are intermediate hosts for which of the following?
- A. Kala azar
- B. Schistosomiasis
- C. Dracunculus medinensis (Correct Answer)
- D. Teniasis
Explanation: **Explanation:** **Correct Answer: C. Dracunculus medinensis** *Dracunculus medinensis* (Guinea worm) is a tissue nematode that requires **Cyclops** (water fleas) as its essential intermediate host. The life cycle begins when a person drinks unfiltered water containing Cyclops infected with L3 larvae. Once inside the human stomach, the Cyclops is digested, releasing the larvae which penetrate the intestinal wall and mature into adults in the subcutaneous tissues. **Analysis of Incorrect Options:** * **A. Kala azar:** Caused by *Leishmania donovani*, this protozoan disease is transmitted by the bite of the female **Sandfly** (*Phlebotomus argentipes*). * **B. Schistosomiasis:** Also known as Bilharzia, these trematodes require specific species of **freshwater snails** (e.g., *Biomphalaria*, *Bulinus*) as intermediate hosts. Infection occurs via skin penetration by cercariae. * **C. Taeniasis:** Caused by *Taenia saginata* (beef tapeworm) or *Taenia solium* (pork tapeworm). The intermediate hosts are **cattle** and **pigs**, respectively. **High-Yield Clinical Pearls for NEET-PG:** * **Cyclops** also serves as the first intermediate host for *Diphyllobothrium latum* (Fish tapeworm) and *Gnathostoma spinigerum*. * **Step-test:** The classic clinical presentation of Dracunculiasis is a painful blister, usually on the lower limb, which ruptures upon contact with water to release larvae. * **Eradication:** India was declared Dracunculiasis-free by the WHO in February 2000. * **Prevention:** Simple filtration of drinking water through a fine cloth (to remove Cyclops) or chemical treatment with Abate (temephos) are key preventive measures.
Practice by Chapter
Classification of Parasites
Practice Questions
Intestinal Protozoa
Practice Questions
Blood and Tissue Protozoa
Practice Questions
Malaria Parasites
Practice Questions
Leishmaniasis
Practice Questions
Intestinal Helminths: Nematodes
Practice Questions
Tissue Nematodes
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Trematodes
Practice Questions
Cestodes
Practice Questions
Ectoparasites
Practice Questions
Antiparasitic Drugs
Practice Questions
Laboratory Diagnosis of Parasitic Infections
Practice Questions
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