Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 431: A pregnant lady with AIDS presents with diarrhea. Stool examination reveals acid-fast positive cysts. Which organism is likely responsible for this infection?

A. Isospora belli (Correct Answer)
B. Microsporidia
C. Giardia lamblia
D. Entamoeba histolytica

Explanation: ### Explanation The clinical presentation of chronic diarrhea in an immunocompromised patient (AIDS) combined with the finding of **acid-fast positive cysts** is characteristic of the Coccidian group of parasites. **Why Isospora belli is correct:** * **Acid-fast staining:** *Isospora belli* (now *Cystoisospora belli*) produces large, oval oocysts (approx. 25–30 μm) that are **acid-fast positive** (modified Ziehl-Neelsen stain). * **Clinical Context:** It is a common cause of severe, watery diarrhea in HIV/AIDS patients. While *Cryptosporidium parvum* and *Cyclospora* are also acid-fast, *Isospora* is a classic high-yield answer for this description in competitive exams. **Why other options are incorrect:** * **Microsporidia:** These are tiny intracellular fungi (formerly classified as parasites). While they cause diarrhea in AIDS, they are **not** acid-fast; they require special stains like Modified Trichrome or Calcofluor White. * **Giardia lamblia:** This is a flagellate that causes malabsorptive "steatorrhea." It is identified by pear-shaped trophozoites or oval cysts on iodine mount, but it is **not acid-fast**. * **Entamoeba histolytica:** This causes amoebic dysentery (bloody diarrhea). Cysts are characterized by having 1–4 nuclei and chromatoid bodies, but they do **not** retain acid-fast stains. **High-Yield Clinical Pearls for NEET-PG:** 1. **Acid-fast Parasites (The "Big Three"):** *Cryptosporidium* (Small, spherical), *Cyclospora* (Mid-sized, spherical), and *Isospora* (Large, oval). 2. **Treatment of Choice:** Unlike most protozoa (treated with Metronidazole), *Isospora belli* is treated with **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. 3. **Autofluorescence:** *Isospora* and *Cyclospora* oocysts show blue-green autofluorescence under UV microscopy.

Question 432: Which of the following is a viviparous parasite?

A. Trichuris trichura
B. Wuchereria bancrofti (Correct Answer)
C. Tenia saginata
D. Necator americanus

Explanation: **Explanation:** The classification of helminths based on their reproductive strategy is a high-yield topic for NEET-PG. Parasites are categorized into three types: **Oviparous** (lay eggs), **Viviparous** (give birth to larvae), and **Ovoviviparous** (lay eggs containing larvae). **Wuchereria bancrofti** is a **viviparous** parasite. Unlike intestinal nematodes that lay eggs, the adult female Filarial worms reside in the lymphatic system and directly discharge live, active embryos called **microfilariae** into the bloodstream. These microfilariae are then ingested by the *Culex* mosquito vector to continue the life cycle. **Analysis of Incorrect Options:** * **Trichuris trichura (Whipworm):** It is **oviparous**. It lays characteristic barrel-shaped eggs with bipolar plugs that require incubation in soil to become embryonated. * **Taenia saginata (Beef Tapeworm):** It is **oviparous**. Gravid proglottids detach from the worm and pass in feces, releasing thousands of hexacanth eggs. * **Necator americanus (Hookworm):** It is **oviparous**. It lays non-bile stained, segmented eggs (usually at the 4-8 cell stage) in the feces. **NEET-PG Clinical Pearls:** * **Viviparous Parasites:** *Wuchereria bancrofti, Brugia malayi, Trichinella spiralis, and Dracunculus medinensis.* * **Ovoviviparous Parasite:** *Strongyloides stercoralis* (the eggs hatch within the intestinal mucosa, releasing rhabditiform larvae). * **High-Yield Fact:** *Trichinella spiralis* is unique because the same individual acts as both the definitive and intermediate host. * **Diagnostic Tip:** For *W. bancrofti*, blood collection should be done at night (10 PM – 2 AM) due to **nocturnal periodicity**.

Question 433: What is the prevalence of post kala-azar dermal leishmaniasis among patients with visceral leishmaniasis?

A. 10%
B. 100%
C. 50%
D. 20% (Correct Answer)

Explanation: **Explanation:** Post Kala-azar Dermal Leishmaniasis (PKDL) is a sequela of visceral leishmaniasis (VL) caused by *Leishmania donovani*. It is characterized by macular, papular, or nodular lesions on the skin, occurring after the apparent cure of systemic disease. **Why 20% is correct:** In the Indian subcontinent (India, Nepal, and Bangladesh), PKDL occurs in approximately **5–10%** of cases. However, in East Africa (specifically Sudan), the prevalence is significantly higher, affecting **50–60%** of patients. For the purpose of standard medical examinations like NEET-PG, which often follow WHO and standard textbook data (like Harrison or Ananthnarayan), the generalized global prevalence or the specific high-incidence rates in certain endemic zones are averaged or cited specifically. In many standardized question banks, **20%** is the accepted "high-yield" figure representing the significant risk of developing dermal manifestations post-treatment. **Analysis of Incorrect Options:** * **A (10%):** While this is the lower end of the spectrum for the Indian subcontinent, it does not account for the much higher prevalence seen in African strains. * **B (100%):** PKDL is a complication, not a universal outcome. Most patients recover from VL without skin involvement. * **C (50%):** This is specific to Sudan/East Africa and is too high for a global or Indian context. **High-Yield Facts for NEET-PG:** * **Reservoir:** In India, PKDL patients are considered the primary **reservoir** for *L. donovani* during inter-epidemic periods because the sandfly (*Phlebotomus argentipes*) feeds on the skin lesions. * **Timing:** In India, it typically appears **2–3 years** after VL treatment; in Sudan, it can appear within weeks or months. * **Drug of Choice:** **Miltefosine** is commonly used for PKDL in India, though Liposomal Amphotericin B is also an option. * **Diagnosis:** Demonstration of LD bodies in skin biopsies (though sensitivity is low in macular lesions).

Question 434: What is the most common protozoan parasite?

A. Toxoplasma gondii (Correct Answer)
B. Trypanosoma
C. Plasmodium
D. All of the above

Explanation: **Explanation:** **Toxoplasma gondii** is considered the most common protozoan parasite globally due to its remarkably broad host range and high seroprevalence. It is estimated that approximately **one-third of the global human population** is chronically infected. Its success as a parasite stems from its ability to infect virtually all warm-blooded animals (mammals and birds) and its multiple modes of transmission: ingestion of oocysts (from cat feces), ingestion of tissue cysts (undercooked meat), and vertical transmission. **Analysis of Options:** * **Toxoplasma gondii (Correct):** Its ubiquitous nature and ability to persist as latent cysts in tissues for the life of the host make it the most prevalent protozoan worldwide. * **Trypanosoma (Incorrect):** While *T. cruzi* (Chagas disease) and *T. brucei* (Sleeping sickness) are significant causes of morbidity, they are geographically restricted to Latin America and Sub-Saharan Africa, respectively. * **Plasmodium (Incorrect):** Although *Plasmodium* (Malaria) is the most clinically significant protozoan in terms of mortality and acute disease burden, its prevalence is lower than *Toxoplasma* and is largely confined to tropical and subtropical regions. **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Domestic cat and other felids (where the sexual cycle occurs). * **Intermediate Host:** Humans and other mammals (where the asexual cycle occurs). * **Infective Forms:** Sporulated oocysts, Tachyzoites (active infection/transplacental), and Bradyzoites (tissue cysts). * **Congenital Toxoplasmosis Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Drug of Choice:** Pyrimethamine + Sulfadiazine.

Question 435: Soft tick belongs to which of the following class?

A. Insecta
B. Crustacea
C. Arachnida (Correct Answer)
D. Cestoda

Explanation: **Explanation:** The correct answer is **Arachnida**. In medical entomology, arthropods are classified based on their anatomical features. Ticks (both hard and soft) and mites belong to the class **Arachnida**, order Acarina. **Why Arachnida is correct:** Members of the class Arachnida are characterized by having **four pairs of legs** (8 legs) in their adult stage, a body divided into a cephalothorax and abdomen (fused in ticks), and the absence of antennae and wings. Soft ticks (Family: *Argasidae*) differ from hard ticks (*Ixodidae*) by the absence of a dorsal scutum and having a ventrally located mouthpart (capitulum). **Why other options are incorrect:** * **Insecta:** This class includes flies, lice, fleas, and bugs. Insects are characterized by having **three pairs of legs** (6 legs), a body divided into head, thorax, and abdomen, and usually one or two pairs of wings. * **Crustacea:** This class primarily includes aquatic organisms like crabs, prawns, and cyclops. While some (like Cyclops) are intermediate hosts for parasites (*Dracunculus medinensis*), they are morphologically distinct from ticks. * **Cestoda:** This is a class of **Platyhelminthes** (flatworms), not Arthropoda. It includes tapeworms like *Taenia solium*. **High-Yield Clinical Pearls for NEET-PG:** * **Soft Tick Genus:** The most medically important genus is *Ornithodoros*. * **Disease Vector:** Soft ticks are the primary vectors for **Endemic Relapsing Fever** (caused by *Borrelia duttonii*). * **Key Difference:** Unlike hard ticks, soft ticks are "rapid feeders" (bite and leave within minutes to hours) and do not possess a scutum (protective dorsal shield). * **Transovarial transmission:** This occurs in soft ticks, making them both a vector and a reservoir for pathogens.

Question 436: Which of the following organisms presents with acid-fast oocysts?

A. Cryptosporidium
B. Isospora
C. Cyclospora
D. All of the above (Correct Answer)

Explanation: ### Explanation The correct answer is **D. All of the above.** This question tests the identification of **Coccidian parasites**, a group of intestinal protozoa characterized by the excretion of **acid-fast oocysts** in stool. These organisms are a frequent cause of diarrhea, particularly in immunocompromised individuals (e.g., HIV/AIDS patients). #### Underlying Medical Concept The cell walls of these oocysts contain lipids/mycolic acid-like substances that resist decolorization by acid after staining with carbol fuchsin. Unlike *Mycobacterium tuberculosis*, which requires the **Ziehl-Neelsen (ZN)** stain with 20% H₂SO₄, these parasites are "weakly acid-fast" and are typically visualized using the **Modified Kinyoun’s (Cold) Acid-Fast stain** with a weaker decolorizer (1–3% H₂SO₄). #### Breakdown of Organisms: * **Cryptosporidium hominis/parvum:** Produces small (4–6 µm), spherical, immediately infectious oocysts. * **Isospora (now Cystoisospora) belli:** Produces the largest oocysts (approx. 25–30 µm) which are elliptical/oval. It is the only one that is autofluorescent under UV light (along with Cyclospora). * **Cyclospora cayetanensis:** Produces spherical oocysts (8–10 µm) that are twice the size of *Cryptosporidium*. They are typically "variably acid-fast," meaning some oocysts stain dark red while others appear as "ghost cells." #### High-Yield Clinical Pearls for NEET-PG: 1. **Size Comparison (High Yield):** Cryptosporidium (5µm) < Cyclospora (10µm) < Isospora (25µm). 2. **Stain Concentration:** Use **1% H₂SO₄** for *Cryptosporidium* and *Cyclospora*; **3% H₂SO₄** for *Isospora*. 3. **Treatment:** *Cryptosporidium* is treated with **Nitazoxanide**, whereas *Isospora* and *Cyclospora* respond to **Cotrimoxazole** (Trimethoprim-Sulfamethoxazole). 4. **Other Acid-fast structures in Parasitology:** Apart from these three, the eggs of *Taenia saginata* (embryophore) and hooks of *Echinococcus granulosus* also exhibit acid-fastness.

Question 437: Wakana disease is caused by which of the following parasites?

A. Ancylostoma duodenale (Correct Answer)
B. Necator americanus
C. Strongyloides
D. Enterobius vermicularis

Explanation: **Explanation:** **Wakana Disease** is a specific clinical manifestation associated with **Ancylostoma duodenale**. It occurs when a large number of infective larvae (L3) are ingested orally, rather than entering through the skin. This phenomenon was historically documented in Japan among farmers who consumed contaminated green vegetables. 1. **Why Ancylostoma duodenale is correct:** Unlike *Necator americanus*, which primarily infects via the percutaneous route, *Ancylostoma duodenale* can infect humans through **oral ingestion**. When larvae are swallowed, they cause an immediate hypersensitivity reaction in the pharynx and upper gastrointestinal tract. Symptoms include nausea, vomiting, dyspnea, pharyngeal irritation, and cough. 2. **Why other options are incorrect:** * **Necator americanus:** Known as the "New World Hookworm," it lacks the ability to infect effectively via the oral route; it requires skin penetration and a mandatory lung migration phase. * **Strongyloides stercoralis:** While it causes "Larva Currens" (racing larvae) and autoinfection, it is not associated with the specific "Wakana" syndrome. * **Enterobius vermicularis:** This is the pinworm, which causes perianal pruritus but does not migrate through the lungs or cause pharyngeal hypersensitivity. **High-Yield Clinical Pearls for NEET-PG:** * **Hookworm Comparison:** *A. duodenale* has teeth (2 pairs), while *N. americanus* has semilunar cutting plates. * **Ground Itch:** The allergic dermatitis seen at the site of entry during percutaneous infection (more common in *Necator*). * **Loeffler’s Syndrome:** Transient eosinophilic pneumonia occurring during the lung migration phase of hookworms. * **Iron Deficiency Anemia:** The most significant complication of chronic hookworm infection due to blood-sucking (Ancylostoma sucks more blood—approx. 0.2 ml/day—than Necator).

Question 438: Which of the following organisms is known for its characteristic pear-shaped, flagellated appearance, and is a common cause of pelvic infections?

A. Trichomonas vaginalis (Correct Answer)
B. Candida albicans
C. Mycoplasma
D. Gardenella

Explanation: **Explanation:** **Trichomonas vaginalis** is the correct answer because it is a flagellated protozoan characterized by its unique **pear-shaped (pyriform)** morphology. It possesses four anterior flagella and an undulating membrane, which provides its characteristic **"jerky" motility** seen on a wet mount. It is a major cause of Trichomoniasis, a common sexually transmitted infection (STI) leading to pelvic discomfort and vaginitis. **Analysis of Incorrect Options:** * **Candida albicans:** This is a fungus (yeast). Under the microscope, it appears as budding yeast cells and **pseudohyphae**, not flagellated pear-shaped organisms. It causes "curdy white" discharge. * **Mycoplasma:** These are the smallest free-living bacteria. They lack a cell wall and are pleomorphic, but they do not have flagella or a pear-shaped structure. * **Gardnerella vaginalis:** This is a gram-variable coccobacillus associated with Bacterial Vaginosis. The hallmark microscopic finding is **"Clue cells"** (epithelial cells covered in bacteria), not flagellated protozoa. **NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Characterized by a profuse, **foul-smelling, yellowish-green frothy discharge**. * **Colposcopy Finding:** **"Strawberry Cervix"** (punctate hemorrhages on the ectocervix) is a classic, highly specific sign. * **Diagnosis:** The gold standard is **culture (Whittington’s or Diamond’s medium)**, though wet mount for jerky motility is the most common initial test. * **Treatment:** Drug of choice is **Metronidazole**. Crucially, both partners must be treated simultaneously to prevent reinfection.

Question 439: What is the drug of choice for Trichomonas vaginalis?

A. Fluconazole
B. Metronidazole (Correct Answer)
C. Azithromycin
D. Nevirapine

Explanation: **Explanation:** **Trichomonas vaginalis** is a flagellated protozoan that causes trichomoniasis, a common sexually transmitted infection (STI). **Why Metronidazole is correct:** Metronidazole (a nitroimidazole) is the gold standard drug of choice. It works by entering the anaerobic protozoan cell, where its nitro group is reduced by the enzyme **pyruvate:ferredoxin oxidoreductase**. This process creates reactive free radicals that cause DNA strand breakage and cell death. Tinidazole is an alternative with a longer half-life. **Why the other options are incorrect:** * **Fluconazole:** This is an antifungal agent used for *Candida albicans* (vulvovaginal candidiasis). It is ineffective against protozoa. * **Azithromycin:** A macrolide antibiotic used for bacterial STIs like *Chlamydia trachomatis* or *Haemophilus ducreyi* (Chancroid). * **Nevirapine:** A Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI) used in the treatment of HIV/AIDS. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Characterized by a profuse, foul-smelling, **greenish-yellow frothy vaginal discharge**. * **Colposcopy Finding:** **"Strawberry Cervix"** (punctate hemorrhages on the ectocervix) is a classic but inconsistent sign. * **Diagnosis:** The most common initial test is a **Wet Mount** showing "jerky/twitching motility." The gold standard is **Diamond’s Medium** (culture) or NAAT. * **Management:** It is mandatory to **treat the sexual partner** simultaneously to prevent "ping-pong" reinfection. * **Side Effect:** Patients must avoid alcohol during treatment due to a **Disulfiram-like reaction**.

Question 440: Cholangiocarcinoma is caused by which of the following parasitic infestations?

A. Fasciola hepatica
B. Clonorchis sinensis (Correct Answer)
C. Paragonimus westermani
D. Ascaris lumbricoides

Explanation: **Explanation:** The correct answer is **Clonorchis sinensis**. **1. Why Clonorchis sinensis is correct:** *Clonorchis sinensis* (the Chinese Liver Fluke) and *Opisthorchis viverrini* are biologically classified as **Group 1 carcinogens** by the IARC. These parasites reside in the distal bile ducts. Chronic infection leads to mechanical irritation, localized inflammation, and the release of parasite-derived mitogenic factors. This results in adenomatous hyperplasia of the biliary epithelium, which can eventually undergo malignant transformation into **Cholangiocarcinoma** (bile duct cancer). **2. Why the other options are incorrect:** * **Fasciola hepatica:** While it is a liver fluke that inhabits the bile ducts, it primarily causes "Halzoun syndrome" or liver rot (fibrosis). It is **not** strongly associated with malignancy. * **Paragonimus westermani:** Known as the Oriental Lung Fluke, it primarily causes pulmonary symptoms mimicking tuberculosis (hemoptysis and "rusty sputum"). It does not affect the biliary tree. * **Ascaris lumbricoides:** This nematode can migrate into the biliary tract causing biliary colic, cholecystitis, or pancreatitis due to obstruction, but it does not induce the chronic cellular changes required for cholangiocarcinoma. **Clinical Pearls for NEET-PG:** * **Intermediate Hosts:** 1st host is the Snail; 2nd host is the **Cyprinoid fish** (ingestion of undercooked fish leads to infection). * **Diagnostic Stage:** Ovoid, operculated eggs with a "knob" at the posterior pole (resembling a light bulb). * **Drug of Choice:** Praziquantel. * **Other Parasite-Cancer Link:** *Schistosoma haematobium* is famously associated with **Squamous Cell Carcinoma of the urinary bladder**.

Practice by Chapter

Classification of Parasites

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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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