Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 11: In the transmission of malaria, what stage of the parasite is transferred by a mosquito bite?

A. Sporozoite (Correct Answer)
B. Merozoite
C. Hypnozoite
D. Gametocyte

Explanation: **Explanation:** The life cycle of *Plasmodium* involves two hosts: the female *Anopheles* mosquito (definitive host) and the human (intermediate host). **Why Sporozoite is correct:** The **Sporozoite** is the infectious stage for humans. When an infected female *Anopheles* mosquito takes a blood meal, it injects saliva containing sporozoites into the human bloodstream. These motile forms travel rapidly to the liver to initiate the **Exo-erythrocytic cycle**. **Analysis of Incorrect Options:** * **Merozoite:** These are released after the rupture of hepatic schizonts (liver stage) or infected RBCs (erythrocytic stage). They are responsible for invading red blood cells, not for initial transmission from the mosquito. * **Hypnozoite:** This is a "dormant" liver stage found specifically in *P. vivax* and *P. ovale*. They remain quiescent in hepatocytes and are responsible for clinical **relapses** months or years later. * **Gametocyte:** These are the sexual forms (male and female) that develop in human RBCs. They are the **infectious stage for the mosquito**, as they are ingested during a blood meal to begin the sporogonic cycle. **High-Yield Clinical Pearls for NEET-PG:** * **Infective stage for humans:** Sporozoite. * **Infective stage for mosquito:** Gametocyte. * **Site of Exflagellation:** Occurs in the midgut of the mosquito (Microgametes). * **Relapse vs. Recrudescence:** Relapse is due to hypnozoites (*P. vivax/ovale*); Recrudescence is due to persistent low-level parasitemia in the blood (*P. falciparum/malariae*). * **Drug of choice for Hypnozoites:** Primaquine (contraindicated in G6PD deficiency).

Question 12: What is the intermediate host of the organism shown here?

A. Snail
B. Cyclops (Correct Answer)
C. Pig
D. Mosquito

Explanation: ***Cyclops*** - **Cyclops** (a copepod crustacean) is the sole intermediate host for **Dracunculus medinensis** (Guinea worm), shown in the image. - Humans become infected by drinking water containing **infected Cyclops**, which release larvae when digested in the stomach. *Snail* - **Snails** serve as intermediate hosts for **schistosomes** (blood flukes) and **liver flukes**, not Guinea worm. - The **miracidium** stage of these parasites penetrates snails to develop into **cercariae**. *Pig* - **Pigs** act as intermediate hosts for **Taenia solium** (pork tapeworm) and **Trichinella spiralis**. - Guinea worm does not require **mammalian intermediate hosts** for its life cycle completion. *Mosquito* - **Mosquitoes** are vectors for **filarial worms** like **Wuchereria bancrofti** and **Brugia malayi**. - They also transmit **malaria parasites** but have no role in **Guinea worm transmission**.

Question 13: What is the most commonly affected tissue in neurocysticercosis?

A. Brain (Correct Answer)
B. Eye
C. Muscles
D. Liver

Explanation: **Explanation:** **Neurocysticercosis (NCC)** is caused by the larval stage (*Cysticercus cellulosae*) of the pork tapeworm, **Taenia solium**. It occurs when humans act as accidental intermediate hosts by ingesting eggs through contaminated food or water (fecal-oral route). **Why the Brain is Correct:** While *Cysticercus cellulosae* can affect various tissues, it has a high tropism for the **Central Nervous System (CNS)**. Within the CNS, the **parenchyma of the brain** is the most common site of involvement. The rich vascular supply to the brain facilitates the lodgment of oncospheres, which then develop into cysts. NCC is the leading cause of adult-onset seizures in developing countries. **Why Other Options are Incorrect:** * **B. Eye:** Ocular cysticercosis occurs in about 1–3% of cases. Cysts are usually found in the subretinal space or vitreous humor, but this is significantly less common than brain involvement. * **C. Muscles:** Subcutaneous and muscular cysticercosis (causing "pseudohypertrophy") are common, but they are often asymptomatic and clinically secondary to the neurological manifestations that define the disease's burden. * **D. Liver:** Unlike *Echinococcus granulosus* (Hydatid cyst), which primarily affects the liver, *T. solium* larvae rarely involve the liver. **NEET-PG High-Yield Pearls:** * **Infective Stage for NCC:** Eggs of *T. solium* (NOT the larvae/cysticerci found in undercooked pork). * **Most Common Presentation:** New-onset seizures (Focal or Generalized). * **Imaging Gold Standard:** MRI is superior to CT for identifying the **scolex** (appears as a "hole-with-dot" or "eccentric dot" sign). * **Drug of Choice:** **Albendazole** (preferred over Praziquantel due to better CNS penetration). Steroids are always co-administered to reduce inflammation from dying cysts.

Question 14: Mucocutaneous Leishmaniasis is caused by which species?

A. L. Brasiliensis (Correct Answer)
B. L. tropica
C. L. donovani
D. L. Chagasi

Explanation: **Explanation:** **Mucocutaneous Leishmaniasis (Espundia)** is primarily caused by the **Leishmania viannia braziliensis** complex. The correct answer is **A**. The underlying medical concept involves the hematogenous or lymphatic spread of the parasite from a primary skin ulcer to the nasopharyngeal and oropharyngeal mucosa. This leads to chronic, disfiguring inflammation and destruction of the nasal septum and soft tissues. **Analysis of Options:** * **L. braziliensis (Correct):** The most common cause of the mucocutaneous form, prevalent in Central and South America (New World Leishmaniasis). * **L. tropica:** Causes **Old World Cutaneous Leishmaniasis** (Oriental Sore/Delhi Boil). It typically remains localized to the skin and does not involve the mucosa. * **L. donovani:** The primary causative agent of **Visceral Leishmaniasis (Kala-azar)**, characterized by fever, hepatosplenomegaly, and pancytopenia. * **L. chagasi:** A New World species that causes Visceral Leishmaniasis (clinically identical to *L. infantum*). **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** All Leishmania species are transmitted by the female **Sandfly** (*Phlebotomus* in the Old World, *Lutzomyia* in the New World). * **Infective Stage:** Promastigote (found in the sandfly). * **Diagnostic Stage:** Amastigote (LD bodies) found within macrophages of the host. * **Drug of Choice:** Liposomal Amphotericin B is the gold standard; Pentavalent antimonials (Sodium Stibogluconate) are also used. * **Montenegro Skin Test:** Positive in Cutaneous and Mucocutaneous forms but **negative** in active Visceral Leishmaniasis (due to deficient cell-mediated immunity).

Question 15: Which of the following is NOT an inhabitant of the liver?

A. Fasciola hepatica
B. Fasciola buski (Correct Answer)
C. Clonorchis sinensis
D. Opisthorchis felinus

Explanation: ### Explanation The correct answer is **Fasciola buski**. The question tests your knowledge of the anatomical localization of trematodes (flukes). Flukes are generally classified based on the organ they inhabit: Liver flukes, Intestinal flukes, Lung flukes, and Blood flukes. **1. Why Fasciola buski is the correct answer:** * **Fasciola buski** is the **Giant Intestinal Fluke**. Unlike the other options, its definitive habitat is the **duodenum and jejunum** of humans and pigs. It attaches to the intestinal mucosa, leading to inflammation, ulceration, and potential obstruction, but it does not inhabit the liver or biliary tract. **2. Analysis of Incorrect Options (Liver Inhabitants):** * **Fasciola hepatica (Sheep Liver Fluke):** Adults reside in the **large biliary passages** of the liver. It causes "Liver Rot" and biliary symptoms. * **Clonorchis sinensis (Chinese Liver Fluke):** Adults inhabit the **distal bile ducts**. Chronic infection is a high-yield risk factor for **Cholangiocarcinoma** (bile duct cancer). * **Opisthorchis felinus (Cat Liver Fluke):** Similar to *Clonorchis*, these reside in the **bile ducts** and are prevalent in parts of Europe and Asia. **3. NEET-PG High-Yield Clinical Pearls:** * **Infective Stage:** For all four parasites listed, the infective stage for humans is the **Metacercaria**. * **Transmission:** *F. hepatica* and *F. buski* are acquired by eating aquatic plants (e.g., water caltrop, watercress). *Clonorchis* and *Opisthorchis* are acquired by consuming raw/undercooked **freshwater fish**. * **Intermediate Hosts:** All trematodes require a **Snail** as their first intermediate host. * **Drug of Choice:** Praziquantel is the DOC for most flukes, **EXCEPT** for *Fasciola hepatica*, where **Triclabendazole** is preferred.

Question 16: A patient presents with itching, rashes, and inguinal lymphadenopathy. Skin snips reveal non-sheathed microfilariae. What is the most probable causative organism?

A. Wuchereria bancrofti
B. Brugia malayi
C. Brugia timori
D. Mansonella streptocerca (Correct Answer)

Explanation: ### Explanation The correct answer is **Mansonella streptocerca**. The diagnosis is based on two key clinical and laboratory findings: the **specimen type (skin snips)** and the **morphology of the microfilariae (non-sheathed)**. **1. Why Mansonella streptocerca is correct:** * **Habitat:** Unlike most filarial worms that reside in the blood or lymphatics, *M. streptocerca* (along with *Onchocerca volvulus*) resides in the **dermis**. Therefore, the diagnostic procedure of choice is a **skin snip**, not a blood film. * **Morphology:** The microfilariae are **unsheathed** and possess a characteristic "walking stick" or "shepherd’s crook" shaped tail. * **Clinical Presentation:** It typically causes dermatological symptoms like pruritic rashes, hypopigmented macules, and inguinal lymphadenopathy (often referred to as "hanging groin" in chronic filarial infections). **2. Why other options are incorrect:** * **Wuchereria bancrofti:** These microfilariae are **sheathed** and are found in the **blood** (showing nocturnal periodicity), not in skin snips. They primarily cause lymphatic filariasis (elephantiasis). * **Brugia malayi & Brugia timori:** Both species produce **sheathed** microfilariae found in the **peripheral blood**. They are characterized by two distinct terminal nuclei at the tip of the tail, which are absent in *Mansonella*. **3. High-Yield Clinical Pearls for NEET-PG:** * **Skin Snip Positive Filariae:** Remember the duo—*Onchocerca volvulus* and *Mansonella streptocerca*. * **Sheath vs. No Sheath:** * *Sheathed:* *W. bancrofti, B. malayi, Loa loa.* * *Unsheathed:* *Onchocerca volvulus, Mansonella* species. * **Vector:** *Mansonella streptocerca* is transmitted by **Culicoides** biting midges. * **Treatment:** Diethylcarbamazine (DEC) is effective against *M. streptocerca*, unlike *Onchocerca* where Ivermectin is preferred.

Question 17: Congenital toxoplasmosis, all are true, except?

A. Occurs in primarily infected mother during pregnancy.
B. As gestational age increases, the risk of transmission to the fetus increases.
C. The infant is usually asymptomatic if infection is transmitted in the 3rd trimester.
D. None of the above. (Correct Answer)

Explanation: **Explanation:** Congenital Toxoplasmosis occurs when *Toxoplasma gondii* is transmitted transplacentally from mother to fetus. The question asks for the "except" (false) statement, and since all options A, B, and C are clinically accurate, the correct answer is **D (None of the above).** 1. **Option A is True:** Congenital transmission occurs almost exclusively when a mother acquires a **primary (new) infection** during pregnancy. In immunocompetent women, chronic/latent infections (positive IgG before pregnancy) do not pose a risk to the fetus as maternal antibodies provide protection. 2. **Option B is True:** There is a direct correlation between gestational age and the risk of transmission. The placenta becomes more permeable as pregnancy progresses. The risk is lowest in the 1st trimester (~15%) and **highest in the 3rd trimester** (~60-70%). 3. **Option C is True:** While the *risk* of transmission is highest in the 3rd trimester, the *severity* of the disease is lowest. Most infants infected late in pregnancy are **asymptomatic at birth**, though they may develop chorioretinitis later in life if untreated. Conversely, 1st-trimester infections are rare but often result in severe damage or miscarriage. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad (Sabin Triad):** Chorioretinitis (most common finding), Hydrocephalus, and Intracranial calcifications (diffuse). * **Diagnosis:** Maternal screening via **Sabin-Feldman Dye Test** (Gold Standard). Fetal diagnosis via PCR of amniotic fluid. * **Treatment:** **Spiramycin** is used to prevent transmission if the mother is infected. If fetal infection is confirmed, **Pyrimethamine, Sulfadiazine, and Folinic acid** are administered.

Question 18: A 35-year-old army captain presents with a painful, erosive lesion near his earlobe that has been present for several years. A punch biopsy of the lesion's leading edge reveals macrophages distended with oval amastigotes. How was this infection most likely acquired?

A. Contact with contaminated drinking water
B. Bite of an infected Anopheles mosquito
C. Bite of an infected reduviid bug
D. Bite of an infected sandfly (Correct Answer)

Explanation: **Explanation:** The clinical presentation describes **Cutaneous Leishmaniasis** (also known as "Oriental Sore" or "Delhi Boil"). The key diagnostic feature provided is the presence of **macrophages distended with oval amastigotes** (LD bodies) in a biopsy from the lesion's edge. 1. **Why Option D is correct:** Leishmaniasis is caused by protozoa of the genus *Leishmania*. It is transmitted to humans through the bite of an infected female **Phlebotomine sandfly**. In the human host, the parasite exists in the **amastigote form** within the phagolysosomes of macrophages. The chronic, erosive nature of the lesion near the ear (often called "Chiclero ulcer" in specific geographic contexts) is a classic manifestation. 2. **Why incorrect options are wrong:** * **Option A:** Contaminated water is associated with enteric pathogens like *Entamoeba histolytica* or *Giardia*, not Leishmania. * **Option B:** *Anopheles* mosquitoes transmit Malaria. While Malaria is a protozoal disease, it presents with systemic febrile illness and involves intracellular stages in RBCs/hepatocytes, not skin ulcers. * **Option C:** Reduviid bugs (Triatomine) transmit *Trypanosoma cruzi* (Chagas disease). While *T. cruzi* also has an amastigote stage, it typically presents with cardiac or gastrointestinal complications, not chronic cutaneous ulcers. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Phlebotomus argentipes* (in India). * **Infective Stage:** Promastigote (found in the sandfly). * **Diagnostic Stage:** Amastigote (LD bodies found in the vertebrate host). * **Culture:** NNN (Novy-MacNeal-Nicolle) medium shows promastigotes. * **Drug of Choice:** Liposomal Amphotericin B (for Visceral); Miltefosine is the only oral drug.

Question 19: Larva of which of the following parasites is typically found in feces?

A. Strongyloides stercoralis (Correct Answer)
B. Taenia solium
C. Taenia saginatum
D. Hymenolepis nana

Explanation: **Explanation:** The correct answer is **Strongyloides stercoralis**. This is a unique helminthic infection because the diagnostic stage found in the stool is the **rhabditiform larva**, rather than the eggs. **1. Why Strongyloides stercoralis is correct:** In the life cycle of *S. stercoralis*, eggs are laid by the adult female in the intestinal mucosa. These eggs hatch almost immediately into rhabditiform larvae within the intestinal lumen. Therefore, by the time the stool is passed, it contains these motile larvae. This is a high-yield distinction, as most other intestinal nematodes are diagnosed by detecting eggs in the feces. **2. Why the other options are incorrect:** * **Taenia solium & Taenia saginata:** The diagnostic stage found in the feces for these tapeworms is either the **proglottid** (segment) or the **embryonated egg**. The larvae (Cysticercus) develop within the intermediate host (pig/cattle) or human tissues, not in the feces. * **Hymenolepis nana:** This parasite is diagnosed by detecting **embryonated eggs** in the stool. While it can undergo internal autoinfection, the larvae (cysticercoids) develop within the intestinal villi and are not typically passed in the feces. **Clinical Pearls for NEET-PG:** * **Autoinfection:** *S. stercoralis* can cause life-threatening **Hyperinfection Syndrome** in immunocompromised patients (e.g., those on steroids or with HTLV-1) because rhabditiform larvae can transform into filariform larvae within the gut and re-enter the circulation. * **Diagnostic Method:** The **Baermann funnel technique** or **Agar plate culture** is used to concentrate and identify these larvae. * **Drug of Choice:** Ivermectin is the preferred treatment for Strongyloidiasis.

Question 20: Which of the following is NOT true about amoebic liver abscess?

A. Adult forms are seen.
B. Conservative treatment is generally employed.
C. Larvae are seen. (Correct Answer)
D. Ultrasonography can aid in diagnosis.

Explanation: Amoebic liver abscess (ALA) is caused by the protozoan parasite **_Entamoeba histolytica_**. Understanding its life cycle is crucial for answering this question. ### **Why "Larvae are seen" is the correct answer (False statement):** _Entamoeba histolytica_ is a **protozoan**, not a helminth (worm). Its life cycle consists only of two stages: the **infective cyst** and the **pathogenic trophozoite**. It does not have a larval stage. Therefore, seeing larvae in a liver abscess is impossible for amoebiasis; larvae would instead suggest a helminthic infection like Hydatid cyst (_Echinococcus granulosus_) or Ascariasis. ### **Analysis of other options:** * **Adult forms are seen:** In protozoology, the "adult" or vegetative stage is the **Trophozoite**. In ALA, trophozoites are found at the periphery of the abscess cavity (the advancing front), where they cause tissue necrosis. * **Conservative treatment is generally employed:** Most cases of ALA respond excellently to medical management with **Metronidazole** or Tinidazole. Surgical aspiration is rarely needed unless the abscess is very large (>10 cm), threatened to rupture, or fails to respond to drugs. * **Ultrasonography can aid in diagnosis:** USG is the first-line imaging modality. It typically shows a hypoechoic, round or oval lesion, usually in the **right lobe** of the liver. ### **High-Yield Clinical Pearls for NEET-PG:** * **Anchovy Sauce Pus:** The aspirated pus is typically reddish-brown, odorless, and sterile (contains no bacteria). * **Trophozoites** are found in the **pus wall**, not usually in the central necrotic debris. * **Route of spread:** From the colon to the liver via the **Portal Vein**. * **Diagnosis:** Stool microscopy is often negative for cysts/trophozoites in 60-90% of ALA cases; **Serology (IHA/ELISA)** is highly sensitive.

Practice by Chapter

Classification of Parasites

Practice Questions

Intestinal Protozoa

Practice Questions

Blood and Tissue Protozoa

Practice Questions

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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