Parasitology Practice Questions

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

Isospora belli. ### 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.

Q: Which of the following is a viviparous parasite?

Wuchereria bancrofti. **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**.

Q: What is the most common protozoan parasite?

Toxoplasma gondii. **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.

Q: Soft tick belongs to which of the following class?

Arachnida. **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.

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

Ancylostoma duodenale. **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).

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

Trichomonas vaginalis. **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.

Q: What is the drug of choice for Trichomonas vaginalis?

Metronidazole. **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**.

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

Clonorchis sinensis. **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**.

Question 1

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

Accepted Answer

Isospora belli

Answer

Microsporidia

Answer

Giardia lamblia

Answer

Entamoeba histolytica

Question 2

Which of the following is a viviparous parasite?

Accepted Answer

Wuchereria bancrofti

Answer

Trichuris trichura

Answer

Tenia saginata

Answer

Necator americanus

Question 3

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

Accepted Answer

20%

Answer

10%

Answer

100%

Answer

50%

Question 4

What is the most common protozoan parasite?

Accepted Answer

Toxoplasma gondii

Answer

Trypanosoma

Answer

Plasmodium

Answer

All of the above

Question 5

Soft tick belongs to which of the following class?

Accepted Answer

Arachnida

Answer

Insecta

Answer

Crustacea

Answer

Cestoda

Question 6

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

Accepted Answer

All of the above

Answer

Cryptosporidium

Answer

Isospora

Answer

Cyclospora

Question 7

Wakana disease is caused by which of the following parasites?

Accepted Answer

Ancylostoma duodenale

Answer

Necator americanus

Answer

Strongyloides

Answer

Enterobius vermicularis

Question 8

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

Accepted Answer

Trichomonas vaginalis

Answer

Candida albicans

Answer

Mycoplasma

Answer

Gardenella

Question 9

What is the drug of choice for Trichomonas vaginalis?

Accepted Answer

Metronidazole

Answer

Fluconazole

Answer

Azithromycin

Answer

Nevirapine

Question 10

Cholangiocarcinoma is caused by which of the following parasitic infestations?

Accepted Answer

Clonorchis sinensis

Answer

Fasciola hepatica

Answer

Paragonimus westermani

Answer

Ascaris lumbricoides

Parasitology — MCQs

Parasitology — MCQs

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