Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 281: Hydrocele and edema in the foot are characteristic clinical findings in infection with which of the following organisms?

A. Wuchereria bancrofti (Correct Answer)
B. Brugia malayi
C. Brugia timori
D. Onchocerca volvulus

Explanation: **Explanation:** The clinical presentation of **hydrocele** and **edema in the foot** (elephantiasis) is characteristic of Lymphatic Filariasis. **1. Why Wuchereria bancrofti is correct:** *Wuchereria bancrofti* is responsible for approximately 90% of lymphatic filariasis cases worldwide. The adult worms reside in the afferent lymphatic vessels and nodes, leading to mechanical obstruction, endothelial proliferation, and eventual fibrosis. While both *Wuchereria* and *Brugia* species cause lower limb edema, **hydrocele (scrotal involvement)** is a hallmark specifically associated with *W. bancrofti*. This is because *W. bancrofti* frequently involves the pelvic and spermatic cord lymphatics, whereas *Brugia* species typically restrict themselves to the lymphatics of the limbs (below the knee or elbow). **2. Why the other options are incorrect:** * **Brugia malayi & Brugia timori:** These species cause "Brugian Filariasis." While they cause significant lymphedema and elephantiasis of the legs, they **rarely involve the genitalia**; thus, hydrocele and chyluria are characteristically absent. * **Onchocerca volvulus:** This parasite causes "River Blindness." Its clinical manifestations are primarily dermatological (subcutaneous nodules, "lizard skin") and ocular (sclerosing keratitis). It does not cause lymphatic obstruction leading to hydrocele. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Culex quinquefasciatus* (most common for *W. bancrofti*). * **Diagnosis:** Presence of sheathed microfilariae with **no nuclei in the tail tip** (distinguishes *W. bancrofti* from *Brugia*). * **Nocturnal Periodicity:** Microfilariae are best detected in peripheral blood between 10 PM and 2 AM. * **Drug of Choice:** Diethylcarbamazine (DEC); however, if co-infected with Onchocerciasis, Ivermectin is preferred to avoid severe reactions. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough and high IgE levels.

Question 282: Which of the following statements best describes intestinal amebae?

A. They are usually nonpathogenic.
B. They are usually transmitted as trophozoites.
C. They can cause peritonitis and liver abscesses. (Correct Answer)
D. They occur most abundantly in the duodenum.

Explanation: ### Explanation **Correct Option: C. They can cause peritonitis and liver abscesses.** *Entamoeba histolytica* is the primary pathogen among intestinal amebae. It possesses proteolytic enzymes (histolysin) that allow it to invade the colonic mucosa, causing "flask-shaped" ulcers. If the ulcer perforates the bowel wall, it leads to **peritonitis**. Furthermore, trophozoites can enter the portal circulation and travel to the liver, where they cause **Amoebic Liver Abscess (ALA)**, characterized by "anchovy sauce" pus. **Why other options are incorrect:** * **Option A:** While many species (like *E. coli* or *E. dispar*) are nonpathogenic, the group includes *E. histolytica*, a major cause of global morbidity. In a clinical/exam context, "intestinal amebae" typically focuses on the significant pathology of *E. histolytica*. * **Option B:** Transmission occurs via the **fecal-oral route** through the ingestion of mature **quadrinucleate cysts**. Trophozoites are labile and are destroyed by gastric acid; they are not the infectious stage. * **Option D:** *E. histolytica* primarily inhabits the **large intestine** (cecum and colon), not the duodenum. (Note: *Giardia* is the parasite typically associated with the duodenum/jejunum). **NEET-PG High-Yield Pearls:** * **Infective Stage:** Mature quadrinucleate cyst. * **Diagnostic Stage:** Trophozoite (containing ingested RBCs/erythrophagocytosis) or cyst in stool. * **Pathognomonic Sign:** Erythrophagocytosis by trophozoites is the definitive feature of *E. histolytica* (distinguishing it from the morphologically identical *E. dispar*). * **Drug of Choice:** Metronidazole or Tinidazole (followed by a luminal amebicide like Paromomycin to eradicate cysts).

Question 283: Which of the following is FALSE about Leishmaniasis?

A. Aldehyde Test of Napier is a good test for diagnosis. (Correct Answer)
B. Indian Leishmaniasis is a non-zoonotic infection with man as the sole reservoir.
C. Co-infection with AIDS is now emerging.
D. There are no drugs for personal prophylaxis.

Explanation: **Explanation:** The correct answer is **A** because the **Aldehyde Test of Napier** is **not** a "good" (specific) test for the diagnosis of Visceral Leishmaniasis (Kala-azar). It is a non-specific biochemical test that relies on hypergammaglobulinemia. It only becomes positive after 3 months of infection and can be falsely positive in other conditions like Multiple Myeloma, Schistosomiasis, and Cirrhosis. Modern diagnosis relies on the **rK39 immunochromatographic test** (highly sensitive/specific) or bone marrow/splenic aspiration. **Analysis of other options:** * **Option B:** Indian Leishmaniasis (*L. donovani*) is unique because it is **anthroponotic** (man is the sole reservoir). In contrast, Leishmaniasis in other parts of the world (e.g., Mediterranean or South America) is often zoonotic, involving canines or rodents. * **Option C:** **Leishmania-HIV co-infection** is a significant emerging public health challenge. HIV increases the risk of developing clinical Leishmaniasis by 100 to 2320 times, and Leishmaniasis accelerates the progression of HIV. * **Option D:** Currently, there are **no vaccines or chemoprophylactic drugs** available for personal prophylaxis against Leishmaniasis. Prevention relies entirely on vector control (sandfly) and personal protective measures (nets/repellents). **High-Yield NEET-PG Pearls:** * **Vector:** Female Sandfly (*Phlebotomus argentipes*). * **Infective stage:** Promastigote; **Diagnostic stage:** Amastigote (LD bodies). * **Drug of Choice:** Liposomal Amphotericin B (Single dose is now the standard in India). * **Post-Kala-azar Dermal Leishmaniasis (PKDL):** Occurs in 10% of cases in India after apparent cure; serves as an important reservoir for transmission.

Question 284: Which of the following is true about Plasmodium falciparum?

A. James dots are seen
B. Accole forms are seen (Correct Answer)
C. Relapses are frequent
D. Longest incubation period

Explanation: **Explanation:** *Plasmodium falciparum* is the most virulent species of malaria, characterized by high levels of parasitemia and specific morphological features in peripheral blood smears. **1. Why "Accole forms" is correct:** In *P. falciparum* infections, young trophozoites (rings) are often seen at the very periphery of the Red Blood Cell (RBC), appearing as if they are "stuck" to the external margin of the cell membrane. These are known as **Accole or Applique forms**. This occurs because *P. falciparum* can infect RBCs of all ages, leading to high density and multiple rings per cell. **2. Why other options are incorrect:** * **James dots:** These are characteristic of *Plasmodium ovale*. In contrast, *P. falciparum* exhibits **Maurer’s dots**, while *P. vivax* shows **Schüffner’s dots**. * **Relapses:** Relapses occur due to the activation of dormant liver stages called **hypnozoites**. These are only found in *P. vivax* and *P. ovale*. *P. falciparum* does not have a hypnozoite stage; therefore, it causes **recrudescence** (due to surviving blood stages), not relapse. * **Longest incubation period:** *P. falciparum* has the **shortest** incubation period (approx. 12 days). The longest incubation period is seen in *P. malariae* (up to 30 days or more). **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Look for **crescent/banana-shaped gametocytes** and multiple rings per RBC. * **Sequestration:** *P. falciparum* causes RBCs to develop "knobs," leading to cytoadherence and sequestration in deep capillaries, which results in **Cerebral Malaria**. * **RBC Age:** It infects RBCs of **all ages**, unlike *P. vivax* (reticulocytes) or *P. malariae* (old RBCs).

Question 285: Pulmonary eosinophilia is seen in the following parasitic infections except?

A. Babesiosis (Correct Answer)
B. Hookworm infection
C. Strongyloidiasis
D. Visceral larva migrans

Explanation: **Explanation:** The concept of **Pulmonary Eosinophilia** (often manifesting as Loeffler’s syndrome) in parasitology refers to the inflammatory response triggered by the migration of helminthic larvae through the lungs. **Why Babesiosis is the correct answer:** Babesiosis is caused by the intraerythrocytic protozoa *Babesia microti*. Unlike helminths, it does not have a migratory larval phase through the lungs. It primarily causes a malaria-like hemolytic anemia. While severe cases can lead to ARDS (Acute Respiratory Distress Syndrome), it does **not** cause peripheral or pulmonary eosinophilia, as eosinophilic responses are characteristic of multicellular helminthic infections, not protozoal ones. **Why the other options are incorrect:** * **Hookworm (*Ancylostoma duodenale/Necator americanus*):** These parasites follow the **"Heart-Lung migration"** path. Larvae penetrate the skin, enter the venous circulation, reach the lungs, break into alveoli, and are coughed up and swallowed. This triggers a Type I hypersensitivity reaction (eosinophilia). * **Strongyloidiasis (*Strongyloides stercoralis*):** Similar to hookworms, these larvae migrate through the lungs. In immunocompromised patients, "Hyperinfection syndrome" can lead to massive pulmonary involvement. * **Visceral Larva Migrans (VLM):** Caused by *Toxocara canis/cati*, the larvae migrate through various organs, including the lungs and liver, causing high-grade peripheral eosinophilia and pulmonary infiltrates. **NEET-PG High-Yield Pearls:** 1. **Loeffler’s Syndrome Mnemonic (NASSA):** **N**ecator americanus, **A**scaris lumbricoides, **S**trongyloides stercoralis, **S**chistosomiasis (early stage), **A**ncylostoma duodenale. 2. **Tropical Pulmonary Eosinophilia (TPE):** A distinct hypersensitivity response to microfilariae (*W. bancrofti/B. malayi*) trapped in the lungs; characterized by nocturnal cough and massive eosinophilia (>3000/µL). 3. **Rule of Thumb:** Protozoal infections (Malaria, Babesia, Amoebiasis) generally **do not** cause eosinophilia.

Question 286: Skin snip is used in the diagnosis of which parasitic infection?

A. Trichinosis
B. Strongyloidiasis
C. Schistosomiasis
D. Onchocerciasis (Correct Answer)

Explanation: **Explanation:** The correct answer is **Onchocerciasis** (River Blindness), caused by the filarial nematode *Onchocerca volvulus*. **1. Why Onchocerciasis is correct:** Unlike most filarial worms that circulate in the blood, the adult female *O. volvulus* resides in subcutaneous nodules and produces larvae called **microfilariae** that migrate specifically through the **dermis (skin)**. A **skin snip** is the gold standard diagnostic test; a small piece of skin is shaved off (without drawing blood) and incubated in saline. The microfilariae emerge from the tissue and are visualized under a microscope. **2. Why other options are incorrect:** * **Trichinosis (*Trichinella spiralis*):** Diagnosis is primarily via **muscle biopsy** (to see encysted larvae) or serology. * **Strongyloidiasis (*Strongyloides stercoralis*):** Diagnosis is usually made by detecting rhabditiform larvae in **stool** (using the Baermann technique) or duodenal aspirates. * **Schistosomiasis:** Diagnosis depends on the species; *S. mansoni* and *S. japonicum* are found in **stool**, while *S. haematobium* is found in **urine**. **Clinical Pearls for NEET-PG:** * **Vector:** Onchocerciasis is transmitted by the **Blackfly (*Simulium*)**. * **Clinical Triad:** Dermatitis (intense itching/“Lizard skin”), subcutaneous nodules (Onchocercomas), and ocular lesions (Sclerosing keratitis leading to blindness). * **Mazzotti Reaction:** An acute inflammatory response (fever, rash) occurring after treatment with **Ivermectin** (the drug of choice) due to the rapid killing of microfilariae. * **Other Skin Snip uses:** It can also be used to diagnose *Mansonella streptocerca*.

Question 287: Which of the following is the infective form for the mosquito in Plasmodium falciparum?

A. Merozoites
B. Sporozoites
C. Gametocytes (Correct Answer)
D. Trophozoites

Explanation: ### Explanation The life cycle of *Plasmodium falciparum* involves two hosts: the **Anopheles mosquito** (definitive host) and the **human** (intermediate host). **Why Gametocytes are correct:** Gametocytes (male microgametocytes and female macrogametocytes) are the sexual stages of the parasite that develop in the human red blood cells. When a female Anopheles mosquito bites an infected human, it ingests these gametocytes. Inside the mosquito's midgut, they initiate the **sporogonic cycle** (sexual reproduction). Therefore, gametocytes are the only stage capable of infecting the mosquito. **Why the other options are incorrect:** * **Sporozoites (Option B):** These are the **infective form for humans**. They are inoculated into the human bloodstream via the mosquito's saliva during a blood meal. * **Merozoites (Option A):** These are released from hepatic cells (exo-erythrocytic stage) or ruptured RBCs (erythrocytic stage). They function to infect new erythrocytes within the human host but cannot survive or initiate infection in the mosquito. * **Trophozoites (Option D):** This is the metabolically active, feeding stage within the human RBC (e.g., the "ring form"). While ingested by the mosquito, they are digested and do not contribute to the transmission cycle. **High-Yield NEET-PG Pearls:** * **Infective form for Human:** Sporozoite. * **Infective form for Mosquito:** Gametocyte. * **Site of Exflagellation:** Occurs in the **mosquito midgut** (microgamete formation). * **Relapse vs. Recrudescence:** *P. falciparum* causes **recrudescence** (due to persistent blood stages); it does **not** have hypnozoites (liver stages), which are responsible for relapses in *P. vivax* and *P. ovale*. * **Crescent-shaped gametocytes:** A pathognomonic diagnostic feature of *P. falciparum* on a peripheral smear.

Question 288: What is the cause of larva currens?

A. Strongyloides stercoralis (Correct Answer)
B. Necator americanus
C. Ankylostoma duodenale
D. Hymenolepis nana

Explanation: **Explanation:** **1. Why Strongyloides stercoralis is Correct:** Larva currens (meaning "racing larva") is a pathognomonic cutaneous manifestation of **Strongyloides stercoralis** infection. It is a form of cutaneous larva migrans caused by the rapid migration of filariform larvae in the dermis. Unlike other larval migrations, larva currens is characterized by its **extreme speed** (moving up to 5–10 cm per hour). It typically presents as an intensely pruritic, erythematous, linear or serpiginous wheal, most commonly found around the perianal region, buttocks, or thighs due to the parasite's unique **autoinfection** cycle. **2. Why the Other Options are Incorrect:** * **Necator americanus & Ancylostoma duodenale (Hookworms):** These cause **Cutaneous Larva Migrans (Ground Itch)**. However, the classic "creeping eruption" is more commonly associated with animal hookworms (*A. braziliense*). Compared to larva currens, these migrations are much slower (only a few millimeters to centimeters per day). * **Hymenolepis nana (Dwarf Tapeworm):** This is a cestode that resides in the intestine. While it also features an internal autoinfection cycle, it does not have a larval skin-migration phase and therefore does not cause larva currens. **3. High-Yield NEET-PG Pearls:** * **Autoinfection:** *S. stercoralis* is unique because rhabditiform larvae can transform into infective filariform larvae within the host's intestine, leading to chronic infection lasting decades. * **Hyperinfection Syndrome:** In immunocompromised patients (especially those on **corticosteroids**), the autoinfection cycle accelerates, leading to massive larval dissemination to organs like the lungs and CNS. * **Diagnosis:** The gold standard is the **Baermann culture technique** or agar plate culture to detect larvae in stool. * **Drug of Choice:** **Ivermectin** is the preferred treatment (superior to Albendazole).

Question 289: DEC provocation test is done in which condition?

A. Filariasis (Correct Answer)
B. Strongyloidiasis
C. Taeniasis
D. Trichuriasis

Explanation: **Explanation:** The **DEC (Diethylcarbamazine) Provocation Test** (also known as the Mazzotti reaction in a modified form) is a diagnostic tool used for **Filariasis**, specifically infections caused by *Wuchereria bancrofti* and *Brugia malayi*. **Why Filariasis is the correct answer:** In many endemic areas, microfilariae exhibit **nocturnal periodicity**, meaning they circulate in the peripheral blood only at night (usually between 10 PM and 2 AM). To avoid waiting until night for a blood draw, a small dose of DEC (usually 100 mg or 2 mg/kg) is administered to the patient during the day. DEC stimulates the microfilariae to emerge from the deep visceral capillaries into the peripheral circulation within 30–60 minutes, allowing for daytime diagnosis via a thick blood smear. **Why other options are incorrect:** * **Strongyloidiasis:** Diagnosis is primarily made via stool examination (Rhabditiform larvae) or the Agar plate culture method. * **Taeniasis:** Diagnosed by identifying proglottids or eggs in stool or using perianal cellophane tape swabs. * **Trichuriasis:** Diagnosed by identifying characteristic "barrel-shaped" eggs with bipolar plugs in the stool. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** DEC is the drug of choice for Lymphatic Filariasis but is **contraindicated** in Onchocerciasis (due to severe Mazzotti reaction) and Loiasis (due to risk of encephalopathy). * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity response to microfilariae; DEC is highly effective here. * **Alternative:** If DEC provocation is not used, the gold standard for detecting adult worms is the **Filarial Antigen Test (ICT)** or **Ultrasound** (Filarial Dance Sign).

Question 290: Which of the following is a sexually transmitted protozoan?

A. Entamoeba histolytica
B. Toxoplasma gondii
C. Trypanosoma cruzi
D. Trichomonas vaginalis (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Trichomonas vaginalis** **1. Why it is correct:** *Trichomonas vaginalis* is a flagellated protozoan and the causative agent of **Trichomoniasis**, the most common non-viral sexually transmitted infection (STI) worldwide. Unlike many other protozoa, it exists **only in the trophozoite stage** (no cyst stage). Because the trophozoite is fragile and cannot survive long in the external environment, it requires direct person-to-person mucosal contact for transmission, making sexual intercourse the primary route of infection. **2. Why the other options are incorrect:** * **A. Entamoeba histolytica:** Primarily transmitted via the **fecal-oral route** through contaminated food or water (ingestion of mature cysts). While sexual transmission (anal-oral) can occur among MSM (men who have sex with men), it is classified fundamentally as an intestinal parasite. * **B. Toxoplasma gondii:** Transmission occurs via ingestion of oocysts from **cat feces**, eating undercooked meat containing tissue cysts, or **transplacentally** (congenital toxoplasmosis). It is not an STI. * **C. Trypanosoma cruzi:** The causative agent of Chagas disease, it is transmitted by the **Reduviid bug (Triatomine)** through infected feces entering a bite wound or mucous membranes. **3. NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Characterized by a profuse, **foul-smelling, yellowish-green frothy vaginal discharge**. * **Colposcopy Finding:** **"Strawberry Cervix"** (Punctate hemorrhages on the cervix) is a classic pathognomonic sign. * **Diagnosis:** **Whiff test** is positive (amine odor with KOH); **Wet mount microscopy** shows "jerky motility" or "twitching motility." * **Treatment:** Drug of choice is **Metronidazole**. Crucially, **both partners must be treated** simultaneously to prevent "ping-pong" reinfection.

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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