Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 41: Transovarian transmission of infection occurs in which of the following vectors?

A. Fleas
B. Ticks
C. Mosquitoes
D. Sandflies (Correct Answer)

Explanation: **Explanation:** **Transovarian transmission** refers to the passage of a pathogen from a female vector to its offspring via the eggs. This mechanism allows the pathogen to persist in the environment even in the absence of a vertebrate host. **Why Sandflies are correct:** In the context of medical parasitology and entomology, sandflies (*Phlebotomus* species) are well-known for the transovarian transmission of **Sandfly fever virus** (Pappataci fever). While sandflies are primarily famous for transmitting *Leishmania donovani*, the vertical transmission of the virus through their eggs ensures the viral reservoir remains stable across generations. **Analysis of Incorrect Options:** * **Fleas:** Primarily transmit *Yersinia pestis* (Plague) via the "blocked flea" mechanism (regurgitation) and *Rickettsia typhi* (Endemic typhus) through feces. Transovarian transmission is not a significant feature. * **Mosquitoes:** While mosquitoes transmit numerous diseases (Malaria, Filaria, Dengue), the pathogens usually require a cycle in the vertebrate host. While some viruses (like West Nile) show low levels of vertical transmission, it is not their defining characteristic compared to the classic examples. * **Ticks:** Ticks are actually the **most classic** example of transovarian transmission (specifically for *Rickettsia rickettsii* and *Babesia*). However, given the specific options provided in this question, Sandflies are the designated correct answer for viral transmission. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Examples of Transovarian Transmission:** Ticks (Babesiosis, Rocky Mountain Spotted Fever) and Sandflies (Sandfly Fever). * **Sandfly (Phlebotomus):** Vector for Kala-azar (Leishmaniasis), Oriental sore, Sandfly fever, and Oroya fever (Bartonellosis). * **Key Vector Fact:** The sandfly is the smallest significant disease-carrying insect; it cannot fly against the wind and hops rather than flies.

Question 42: Which of the following infections is diagnosed by the aldehyde test?

A. Fasciola hepatica
B. Leishmania (Correct Answer)
C. Toxoplasma
D. Toxocara canis

Explanation: **Explanation:** The **Aldehyde Test (Napier’s Aldehyde Test)** is a non-specific biochemical test used for the presumptive diagnosis of **Visceral Leishmaniasis (Kala-azar)** caused by *Leishmania donovani*. **Mechanism:** The test detects **hypergammaglobulinemia** (a massive increase in IgG levels). When a drop of 40% formalin is added to 1-2 ml of the patient's serum, the serum gels and becomes opaque (like the white of a boiled egg) within 2–20 minutes. A positive result indicates a chronic systemic inflammatory response typical of late-stage Kala-azar. **Analysis of Options:** * **Leishmania (Correct):** It is the classic association for this test. Note that the test only becomes positive after the infection has lasted for at least 3 months. * **Fasciola hepatica:** Diagnosed primarily by stool microscopy (detecting operculated eggs) or ELISA for antibodies; it does not produce the specific protein profile required for a positive aldehyde test. * **Toxoplasma:** Diagnosis relies on serology (IgM/IgG) or PCR. While it causes lymphadenopathy, it doesn't cause the massive polyclonal gammopathy seen in Leishmania. * **Toxocara canis:** Causes Visceral Larva Migrans; diagnosis is based on clinical presentation and ELISA (Excretory-Secretory antigens). **High-Yield Clinical Pearls for NEET-PG:** * **Specificity:** The Aldehyde test is **non-specific**. It can also be positive in Multiple Myeloma, Schistosomiasis, Trypanosomiasis, and Leprosy. * **Chopra’s Antimony Test:** Another non-specific test for Kala-azar using urea stibamine. * **Gold Standard:** Bone marrow or splenic aspiration (demonstrating **LD bodies**). * **RK-39 Immunochromatographic strip:** The current rapid diagnostic test of choice for field use.

Question 43: Leaf-like helminths are also known by what name?

A. Flukes (Correct Answer)
B. Roundworms
C. Tapeworms
D. Cestodes

Explanation: **Explanation:** Helminths (parasitic worms) are classified into three main groups based on their morphology: Trematodes, Cestodes, and Nematodes. **1. Why "Flukes" is correct:** **Flukes (Trematodes)** are characterized by their **leaf-like, unsegmented, and flattened** bodies. They possess two suckers (oral and ventral/acetabulum) for attachment to host tissues. Most flukes are hermaphroditic (except *Schistosoma*). Their unique leaf shape is the primary morphological feature used to distinguish them from other helminths. **2. Why the other options are incorrect:** * **Roundworms (Nematodes):** These are cylindrical, elongated, and unsegmented worms with a complete digestive tract. They are not flattened or leaf-like. Examples include *Ascaris lumbricoides* and Hookworms. * **Tapeworms (Cestodes):** While these are flat, they are **ribbon-like and segmented** (proglottids). They lack a digestive tract and are much longer than flukes. * **Cestodes:** This is simply the scientific name for tapeworms, which, as mentioned, are ribbon-shaped rather than leaf-shaped. **High-Yield Clinical Pearls for NEET-PG:** * **Exception to the "Leaf-shape" rule:** *Schistosoma* (Blood flukes) are elongated and cylindrical, resembling roundworms, but are biologically classified as Trematodes. * **Exception to Monoecious (Hermaphroditic) rule:** All Trematodes are hermaphroditic except *Schistosoma*, which are dioecious (separate sexes). * **Intermediate Host:** All Trematodes require a **snail** as their first intermediate host. * **Infective Stage:** For most flukes, it is the **Metacercaria**, but for *Schistosoma*, it is the **Cercaria** (via skin penetration).

Question 44: What is the causative agent of River blindness?

A. Onchocerca volvulus (Correct Answer)
B. Loa loa
C. Wuchereria bancrofti
D. All of the above

Explanation: **Explanation:** **Onchocerca volvulus** is the correct answer as it is the causative agent of **Onchocerciasis**, commonly known as **River Blindness**. The disease is transmitted through the bite of the **Simulium fly (Blackfly)**, which breeds in fast-flowing rivers. The pathology is primarily caused by the host's inflammatory response to dying microfilariae in the skin and eyes, leading to sclerosing keratitis and eventual blindness. **Analysis of Incorrect Options:** * **Loa loa:** Also known as the "African eye worm," it causes **Calabar swellings** (fugitive swellings). While the adult worm can be seen migrating across the subconjunctiva of the eye, it typically does not cause blindness. It is transmitted by the *Chrysops* fly (Deer fly). * **Wuchereria bancrofti:** This is the primary agent of **Lymphatic Filariasis**. It targets the lymphatic system, leading to lymphedema and elephantiasis (usually of the lower limbs and scrotum). It is transmitted by the *Culex* mosquito and does not involve ocular pathology. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Simulium* fly (Blackfly). * **Clinical Triad:** Dermatitis (intense itching/Lizard skin), Subcutaneous nodules (Onchocercomas), and Ocular lesions (River blindness). * **Diagnosis:** **Skin snip test** is the gold standard (to demonstrate microfilariae). Note: Microfilariae are NOT found in the blood (non-sheathed). * **Treatment:** **Ivermectin** is the drug of choice (DOC). It kills microfilariae but not adult worms. * **Mazzotti Reaction:** A severe systemic reaction (fever, rash, hypotension) that can occur after treating Onchocerciasis with Diethylcarbamazine (DEC) due to the rapid killing of microfilariae.

Question 45: Which of the following acts as a vector for spreading Onchocerciasis?

A. Tsetse fly
B. Culicoides midge
C. Simulium damnosum (Correct Answer)
D. Bugs of subfamily Triatominae

Explanation: **Explanation:** **Onchocerciasis**, also known as **River Blindness**, is caused by the filarial nematode *Onchocerca volvulus*. The correct answer is **Simulium damnosum** (the Blackfly), which serves as the intermediate host and biological vector. 1. **Why Option C is Correct:** The transmission occurs when an infected female *Simulium* fly bites a human to take a blood meal, depositing **L3 (infective) larvae** into the skin. These flies breed in fast-flowing rivers and streams (hence the name "River Blindness"). The larvae mature into adults in subcutaneous nodules and release microfilariae, which migrate through the skin and eyes, leading to severe dermatitis and ocular lesions. 2. **Why Other Options are Incorrect:** * **A. Tsetse fly (*Glossina*):** The vector for African Trypanosomiasis (Sleeping Sickness). * **B. Culicoides midge:** The vector for *Mansonella* species (specifically *M. ozzardi* and *M. perstans*). * **D. Triatomine bugs (Kissing bugs):** The vector for *Trypanosoma cruzi*, which causes Chagas disease. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Triad:** Subcutaneous nodules (Onchocercomas), Dermatitis (Lizard skin/Leopard skin), and Ocular changes (Sclerosing keratitis). * **Diagnosis:** The gold standard is the **Skin Snip Test** to demonstrate microfilariae (Note: Microfilariae are NOT found in the blood). * **Mazzotti Reaction:** A severe systemic reaction (fever, rash, hypotension) occurring after treatment with Diethylcarbamazine (DEC) due to the rapid killing of microfilariae. * **Drug of Choice:** **Ivermectin** (DEC is generally avoided due to the Mazzotti reaction). * **Endosymbiont:** *Onchocerca* harbors *Wolbachia* bacteria; treating with Doxycycline can sterilize adult female worms.

Question 46: Which of the following best describes lice?

A. They have wings
B. They cause tissue edema
C. They transmit epidemic typhus, relapsing fever, and trench fever (Correct Answer)
D. Pediculus humanus is the only species of louse

Explanation: **Explanation:** Lice (specifically *Pediculus humanus corporis*, the body louse) are significant medical vectors. The correct option (C) is right because the body louse is the definitive vector for three major bacterial diseases: 1. **Epidemic Typhus:** Caused by *Rickettsia prowazekii*. 2. **Epidemic Relapsing Fever:** Caused by *Borrelia recurrentis*. 3. **Trench Fever:** Caused by *Bartonella quintana*. **Analysis of Incorrect Options:** * **Option A:** Lice are **wingless** (Aptera) ectoparasites. They move by crawling and use specialized claws to grip hair or clothing fibers. * **Option B:** While lice bites cause pruritus (itching) and papules due to saliva hypersensitivity, they are not classically associated with significant **tissue edema**. Their primary clinical manifestation is "Vagabond's disease" (hyperpigmentation and thickening of the skin in chronic infestations). * **Option D:** *Pediculus humanus* is not the only species. There are three distinct types affecting humans: *Pediculus humanus capitis* (head louse), *Pediculus humanus corporis* (body louse), and *Pthirus pubis* (crab/pubic louse). **High-Yield NEET-PG Pearls:** * **Vector Specificity:** Only the **body louse** transmits diseases; head lice and pubic lice are nuisances but not vectors. * **Transmission Mechanism:** *Rickettsia prowazekii* is transmitted via **posterior station** (infected feces rubbed into bite wounds), whereas *Borrelia recurrentis* is transmitted when the louse is **crushed** and the hemolymph contacts broken skin. * **Treatment:** Drug of choice for infestation is **Permethrin (1%)** or Ivermectin. * **Nits:** These are louse eggs firmly cemented to hair shafts; their distance from the scalp can help estimate the duration of infestation.

Question 47: Which of the following nematodes is ovoviviparous?

A. Ascaris lumbricoides
B. Dracunculus medinensis
C. Strongyloides stercoralis (Correct Answer)
D. Enterobius vermicularis

Explanation: **Explanation:** Nematodes are classified based on their mode of reproduction into three categories: **Oviparous** (lay eggs), **Viviparous** (give birth to larvae), and **Ovoviviparous** (lay eggs containing larvae that hatch immediately). **Why Strongyloides stercoralis is correct:** *Strongyloides stercoralis* is classically described as **ovoviviparous**. The parasitic female inhabits the submucosa of the small intestine and lays embryonated eggs. These eggs hatch almost immediately within the intestinal mucosa, releasing **rhabditiform larvae**. Consequently, in a stool examination, larvae are typically seen rather than eggs. This unique feature also allows for "autoinfection," where larvae mature into the filariform stage within the host's body. **Analysis of Incorrect Options:** * **Ascaris lumbricoides:** It is **oviparous**. It lays unsegmented eggs that require a period of incubation in the soil to become embryonated and infective. * **Dracunculus medinensis:** It is **viviparous**. The gravid female residing in subcutaneous tissue discharges live larvae (L1) directly into the water when the host's skin comes into contact with it. * **Enterobius vermicularis:** It is **oviparous**. The female migrates to the perianal skin to lay eggs. While these eggs become infective quickly (within 6 hours), they are laid as eggs, not larvae. **High-Yield Clinical Pearls for NEET-PG:** * **Viviparous Nematodes:** *Trichinella spiralis, Wuchereria bancrofti, Brugia malayi, Dracunculus medinensis.* * **Strongyloides "Rule of Threes":** It is the only nematode that causes **autoinfection**, can exist in a **free-living cycle** in soil, and is diagnosed by finding **larvae in stool** (not eggs). * **Hyperinfection Syndrome:** In immunocompromised patients (e.g., those on steroids), *Strongyloides* can lead to massive larval dissemination.

Question 48: Dermal leishmaniasis is caused by all of the following parasites except:

A. L. tropica
B. L. major
C. L. aethiopica
D. None of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **None of the above** because all three listed species—*L. tropica*, *L. major*, and *L. aethiopica*—are well-established causative agents of **Old World Cutaneous (Dermal) Leishmaniasis**. 1. **L. tropica:** This species is the primary cause of **Urban Cutaneous Leishmaniasis** (Dry sore). It typically presents as a single, painless ulcer that heals slowly over a year, often leaving a scar. 2. **L. major:** This species causes **Rural Cutaneous Leishmaniasis** (Wet sore). It is zoonotic (carried by rodents) and characterized by rapidly developing, inflamed, and exudative ulcers. 3. **L. aethiopica:** Found primarily in East Africa, it causes cutaneous leishmaniasis and is uniquely associated with **Diffuse Cutaneous Leishmaniasis (DCL)** in immunocompromised individuals, where nodular lesions spread across the body without ulceration. Since all options (A, B, and C) are known causes of dermal leishmaniasis, the "except" condition is not met by any of them, making "None of the above" the correct choice. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** All forms of Leishmaniasis are transmitted by the bite of the female **Sandfly** (*Phlebotomus* in the Old World; *Lutzomyia* in the New World). * **Infective Stage:** Promastigote (flagellated form found in the sandfly). * **Diagnostic Stage:** Amastigote (LD bodies found within macrophages in humans). * **Leishmanin (Montenegro) Test:** This delayed hypersensitivity skin test is **positive** in Cutaneous Leishmaniasis but **negative** in active Visceral Leishmaniasis (Kala-azar) and Diffuse Cutaneous Leishmaniasis (DCL).

Question 49: Larvae of which of the following lies parallel to the surface of water?

A. Anopheles (Correct Answer)
B. Culex
C. Aedes
D. Sandfly

Explanation: The correct answer is **Anopheles**. ### **Explanation** The orientation of mosquito larvae in water is a classic high-yield distinction in medical entomology. * **Anopheles:** The larvae lack a respiratory siphon. To breathe, they must lie **parallel (horizontal)** to the water surface to allow their posterior respiratory spiracles to make direct contact with the air. They are often referred to as "surface feeders." * **Culex and Aedes:** These larvae possess a **respiratory siphon** (a tube-like structure). This allows them to hang **at an angle (obliquely)** from the water surface while breathing, with only the tip of the siphon piercing the surface film. * **Sandfly:** This is a distractor. Sandflies (*Phlebotomus*) do not have an aquatic life cycle; their larvae develop in moist soil rich in organic matter, not in standing water. ### **High-Yield Clinical Pearls for NEET-PG** To differentiate these vectors quickly, remember these "Rule of Opposites": | Feature | Anopheles | Culex / Aedes | | :--- | :--- | :--- | | **Larva Position** | Parallel to surface | At an angle (Oblique) | | **Siphon Tube** | Absent | Present | | **Adult Resting** | At an angle (45°) | Parallel to surface | | **Eggs** | Laid singly with lateral floats | Rafts (Culex) / Singly without floats (Aedes) | | **Feeding Time** | Night biters | Day biters (Aedes) / Night biters (Culex) | **Key Disease Associations:** * **Anopheles:** Vector for Malaria. * **Culex:** Vector for Japanese Encephalitis, West Nile Virus, and Bancroftian Filariasis. * **Aedes:** Vector for Dengue, Chikungunya, Zika, and Yellow Fever.

Question 50: Which of the following is a non-lymphatic filarial worm?

A. Loa loa (Correct Answer)
B. Wuchereria bancrofti
C. Brugia malayi
D. Brugia timori

Explanation: ### Explanation Filarial worms (nematodes) are classified based on the anatomical site where the adult worms reside in the human body. They are broadly categorized into **Lymphatic**, **Subcutaneous**, and **Serous cavity** filariae. **1. Why Loa loa is the correct answer:** *Loa loa* (the African Eye Worm) is a **subcutaneous filarial worm**. The adult worms migrate through the subcutaneous tissues, often causing transient localized swellings known as **Calabar swellings**. They are frequently seen migrating across the subconjunctiva of the eye. Unlike the other options, they do not inhabit the lymphatic system. **2. Why the other options are incorrect:** * **Wuchereria bancrofti:** This is the most common cause of lymphatic filariasis worldwide (responsible for ~90% of cases). The adult worms reside in the afferent lymphatic vessels and lymph nodes. * **Brugia malayi:** A major cause of lymphatic filariasis, primarily found in South and Southeast Asia. Like *W. bancrofti*, it targets the lymphatic system. * **Brugia timori:** A less common species restricted to the Timor Islands of Indonesia, it also causes lymphatic filariasis. **3. NEET-PG High-Yield Clinical Pearls:** * **Vector:** *Loa loa* is transmitted by the **Chrysops** fly (deer fly/mango fly), whereas lymphatic filariae are transmitted by mosquitoes (*Culex, Anopheles, Aedes*). * **Microfilariae Periodicity:** *Loa loa* microfilariae exhibit **diurnal periodicity** (present in peripheral blood during the day), whereas *W. bancrofti* usually shows nocturnal periodicity. * **Drug of Choice:** **Diethylcarbamazine (DEC)** is the treatment of choice for both lymphatic filariasis and Loiasis, but caution is required in Loiasis due to the risk of encephalopathy if microfilarial loads are very high. * **Other Subcutaneous Filariae:** *Onchocerca volvulus* (causes River Blindness) and *Mansonella streptocerca*.

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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