Parasitology — MCQs

A 20-year-old male presented with high-grade fever, groin pain, and a swollen scrotum for 1 week, which has been worsening progressively. On examination, he has tender inguinal lymphadenopathy, scrotal swelling with hydrocele, and lymphatic streaking. Blood samples reveal a suspected parasitic infection. The disease is transmitted by which of the following vectors?

Q627Easy

Which of the following is classified as a lung fluke?

Q628Medium

Saturated salt solution concentrates the eggs of which of the following parasites, except?

Q629Easy

Which larva is typically found encysted in muscle tissue?

Q630Easy

In the transmission of malaria, what stage is transferred by a mosquito bite?

Parasitology Indian Medical PG Practice Questions and MCQs

Question 621: A definitive diagnosis of ascariasis can be made by observing which of the following?

A. An adult worm passed during a bowel movement (Correct Answer)
B. Larvae in an x-ray of the lungs
C. Motile larvae in a stool sample
D. Eosinophilia in a differential white blood cell count

Explanation: ### Explanation **1. Why Option A is Correct:** A definitive diagnosis in parasitology requires the direct visualization of the parasite (eggs, larvae, or adult worms) from clinical specimens. *Ascaris lumbricoides* is the largest intestinal nematode. The most common and definitive ways to diagnose it are by identifying the characteristic **bile-stained eggs** in a stool microscopy or by the **gross identification of an adult worm** passed via the anus, mouth, or nose. Seeing the adult worm provides an indisputable, "gold standard" visual confirmation of the infection. **2. Why Other Options are Incorrect:** * **Option B:** Larvae are microscopic and cannot be seen on a standard X-ray. While X-rays may show "Loeffler’s syndrome" (transient pulmonary infiltrates), this is a non-specific radiological finding, not a definitive visualization of the parasite. * **Option C:** Unlike *Strongyloides stercoralis*, where larvae are the diagnostic stage in stool, *Ascaris* eggs hatch in the small intestine, and the larvae immediately migrate to the lungs. Therefore, **larvae are not typically found in stool samples**; only eggs or adult worms are. * **Option D:** Eosinophilia is a common finding during the larval migration phase (Loeffler’s syndrome), but it is a non-specific systemic response seen in many parasitic infections and allergic conditions. It is suggestive, not definitive. **3. NEET-PG High-Yield Pearls:** * **Diagnostic Stage:** Eggs in feces (most common) or adult worms. * **Infective Stage:** Embryonated eggs (not fresh eggs). * **Loeffler’s Syndrome:** Characterized by fever, cough, wheezing, and eosinophilia during the lung migration phase. * **Complications:** Most common is **Intestinal Obstruction** (at the ileocecal valve) and **Biliary Ascariasis**. * **Deworming:** Albendazole is the drug of choice; it works by inhibiting microtubule synthesis.

Question 622: All of the following are true regarding transfusion malaria EXCEPT:

A. Sporozoites transmit it (Correct Answer)
B. Incubation period is shorter
C. Transmitted by merozoites and erythrocytic stages
D. There is no pre-erythrocytic stage

Explanation: ### Explanation The correct answer is **A. Sporozoites transmit it**. In **transfusion malaria**, the infection is acquired through the transfusion of blood containing the parasite. The key concept here is the life cycle stage involved: 1. **Why Option A is the correct (false) statement:** Sporozoites are the infective stage found in the salivary glands of the female *Anopheles* mosquito. They are introduced into the human body during a mosquito bite and immediately head to the liver. In blood transfusion, the donor’s blood contains **erythrocytic stages (merozoites/trophozoites)**, not sporozoites. Therefore, transfusion malaria is transmitted by merozoites. 2. **Why Option B is wrong (True statement):** The incubation period is shorter because the parasite bypasses the time-consuming liver phase (pre-erythrocytic schizogony) and enters the bloodstream directly to start infecting RBCs. 3. **Why Option C is wrong (True statement):** As mentioned, the infection is initiated by the asexual erythrocytic stages (merozoites) present in the donor's red cells. 4. **Why Option D is wrong (True statement):** Since sporozoites are absent, there is no **pre-erythrocytic (liver) stage**. Consequently, there is no risk of **relapse** (hypnozoites) in *P. vivax* or *P. ovale* infections acquired via transfusion, as hypnozoites only form during the liver stage. ### High-Yield Clinical Pearls for NEET-PG: * **Relapse vs. Recrudescence:** Transfusion malaria cannot cause relapse because there is no hepatic phase. * **Screening:** *P. falciparum* is the most common species transmitted via transfusion. * **Storage:** Malarial parasites can survive in blood stored at 4°C for up to 2–3 weeks. * **Drug of Choice:** Since there is no liver stage, **Primaquine is NOT required** for radical cure in transfusion-induced *P. vivax*; Chloroquine alone is sufficient.

Question 623: What is the causative agent for 'Oriental sore'?

A. Leishmania donovoni
B. Leishmania tropica (Correct Answer)
C. Leishmania braziliensis
D. Onchocerca volvulus

Explanation: **Explanation:** **Oriental sore** is a form of Old World Cutaneous Leishmaniasis. It is primarily caused by **Leishmania tropica** (dry/urban type) and *Leishmania major* (wet/rural type). The disease is characterized by a self-limiting ulcer that develops at the site of a sandfly bite, typically on exposed skin. The parasite exists in the amastigote form within macrophages in the skin, leading to a granulomatous reaction. **Analysis of Options:** * **Leishmania tropica (Correct):** The classic cause of "Oriental sore" or "Delhi boil." It produces a dry ulcer that has a long incubation period and heals slowly with scarring. * **Leishmania donovani (Incorrect):** This species causes **Visceral Leishmaniasis** (Kala-azar), characterized by fever, hepatosplenomegaly, and pancytopenia. It does not typically cause primary skin ulcers. * **Leishmania braziliensis (Incorrect):** This species is responsible for **Mucocutaneous Leishmaniasis** (Espundia) in the New World (Americas), affecting the mucous membranes of the nose and mouth. * **Onchocerca volvulus (Incorrect):** A helminth (filarial nematode) that causes "River Blindness." It is transmitted by the Blackfly (*Simulium*) and is not related to the Leishmania genus. **NEET-PG High-Yield Pearls:** * **Vector:** All Leishmania species are transmitted by the female **Sandfly** (*Phlebotomus* species). * **Infective Stage:** Promastigote (found in the sandfly). * **Diagnostic Stage:** Amastigote (LD bodies found in human macrophages). * **Culture:** NNN (Novy-MacNeal-Nicolle) medium is used to grow the promastigote form. * **Leishmanin (Montenegro) Test:** Positive in Cutaneous Leishmaniasis (delayed hypersensitivity) but **negative** in active Visceral Leishmaniasis.

Question 624: A 23-year-old male presents with a painless penile ulcer and painless lymphadenopathy. What is the most likely diagnosis?

A. Chancroid
B. Donovanosis
C. Syphilis (Correct Answer)
D. Herpes

Explanation: ### Explanation The clinical presentation of a **painless penile ulcer** (chancre) accompanied by **painless regional lymphadenopathy** is the classic hallmark of **Primary Syphilis**, caused by the spirochete *Treponema pallidum*. #### Why Syphilis is Correct: The primary chancre typically appears 3–4 weeks after exposure. It is characterized by a clean base, indurated (hard) edges, and a lack of exudate. Crucially, both the ulcer and the associated inguinal lymphadenopathy are **painless**, which distinguishes it from most other genital ulcerative diseases. #### Why Other Options are Incorrect: * **Chancroid (*Haemophilus ducreyi*):** Presents as a **painful**, soft ulcer with a ragged, undermined edge and a necrotic base. The associated lymphadenopathy (bubo) is also exquisitely painful. * **Donovanosis (Granuloma Inguinale):** Caused by *Klebsiella granulomatis*. It presents as beefy-red, painless, velvety ulcers. However, it is characterized by **pseudobuboes** (subcutaneous granulation) rather than true lymphadenopathy. * **Herpes (HSV-2):** Presents as multiple, small, **painful** vesicles that rupture to form shallow ulcers. It is often associated with systemic symptoms like fever and painful lymphadenopathy. #### NEET-PG High-Yield Pearls: * **Investigation of Choice:** Dark-field microscopy is the gold standard for primary syphilis (shows corkscrew motility). * **Hard Chancre:** Syphilis; **Soft Chancre:** Chancroid. * **Donovan Bodies:** Seen on tissue smears (Wrights/Giemsa stain) as "safety-pin" appearing organisms within macrophages (pathognomonic for Donovanosis). * **Rule of Thumb:** If the ulcer hurts, think Chancroid or Herpes; if it doesn't, think Syphilis or LGV (though LGV usually has painful nodes—the "Sign of the Groove").

Question 625: What is the investigation of choice for hydatid disease?

A. CT scan
B. Elisa
C. Biopsy
D. USG (Correct Answer)

Explanation: **Explanation:** Hydatid disease, caused by the larval stage of *Echinococcus granulosus*, most commonly affects the liver. **Why USG is the Investigation of Choice (IOC):** Ultrasonography (USG) is considered the investigation of choice because it is highly sensitive, non-invasive, cost-effective, and widely available. It is the gold standard for **screening and classification** (WHO-IWGE classification). USG can accurately identify pathognomonic features such as the "double-line sign," "water lily sign" (detached endocyst), and "honeycomb appearance" (daughter cysts), which are diagnostic of the disease. **Analysis of Other Options:** * **CT Scan:** While CT is more sensitive for detecting calcification and identifying extra-hepatic cysts or complications, it is generally reserved for cases where USG is inconclusive or for surgical planning. It is not the primary screening tool. * **ELISA:** Serology is used to **confirm** the diagnosis after imaging suggests a cyst. However, it can yield false negatives in calcified or inactive cysts and cannot determine the stage or viability of the cyst. * **Biopsy:** **Strictly contraindicated.** Fine-needle aspiration or biopsy carries a high risk of anaphylactic shock and peritoneal seeding due to the leakage of highly antigenic hydatid fluid. **High-Yield Clinical Pearls for NEET-PG:** * **Casoni’s Test:** An immediate hypersensitivity skin test (historical interest; largely replaced by serology). * **Treatment of Choice:** Surgical excision (PAIR technique or Laparoscopic/Open surgery) combined with **Albendazole**. * **PAIR Technique:** Puncture, Aspiration, Injection (scolicidal agents like hypertonic saline), and Re-aspiration. * **Most common site:** Liver (Right lobe > Left lobe), followed by the Lungs.

Question 626: A 20-year-old male presented with high-grade fever, groin pain, and a swollen scrotum for 1 week, which has been worsening progressively. On examination, he has tender inguinal lymphadenopathy, scrotal swelling with hydrocele, and lymphatic streaking. Blood samples reveal a suspected parasitic infection. The disease is transmitted by which of the following vectors?

A. Aedes mosquito
B. Culex mosquito (Correct Answer)
C. Phlebotomus sandfly
D. Anopheles mosquito

Explanation: ### Explanation **Correct Answer: B. Culex mosquito** **Medical Concept:** The clinical presentation of high-grade fever, painful inguinal lymphadenopathy (lymphadenitis), scrotal swelling (hydrocele), and lymphatic streaking (retrograde lymphangitis) is classic for **Lymphatic Filariasis**, most commonly caused by *Wuchereria bancrofti*. In India, *W. bancrofti* accounts for ~98% of cases. The primary vector for *W. bancrofti* is the **Culex quinquefasciatus** mosquito, which typically breeds in stagnant, polluted water. **Analysis of Options:** * **A. Aedes mosquito:** Primarily transmits Dengue, Chikungunya, Yellow Fever, and Zika. While it can transmit *Brugia malayi* in specific geographical pockets, it is not the primary vector for urban lymphatic filariasis. * **C. Phlebotomus sandfly:** This is the vector for **Leishmaniasis** (Kala-azar). Clinical features include massive splenomegaly and hyperpigmentation, not acute lymphangitis or hydrocele. * **D. Anopheles mosquito:** The principal vector for **Malaria**. While it can transmit filariasis in certain rural areas, *Culex* remains the classic and most common answer for NEET-PG purposes regarding *W. bancrofti*. **Clinical Pearls for NEET-PG:** * **Diagnostic Gold Standard:** Demonstration of microfilariae in a **peripheral blood smear** collected at night (**Nocturnal Periodicity**, 10 PM – 2 AM). * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough, wheezing, and high peripheral eosinophilia. * **Drug of Choice:** **Diethylcarbamazine (DEC)**. Note: DEC is contraindicated in Onchocerciasis due to the Mazzotti reaction. * **Filarial Dance Sign:** Characteristic rhythmic movement of live adult worms seen on scrotal ultrasound.

Question 627: Which of the following is classified as a lung fluke?

A. Echinococcus
B. Paragonimus (Correct Answer)
C. Trichinella
D. Fasciola

Explanation: **Explanation:** **Paragonimus westermani** (the Oriental lung fluke) is the correct answer. It is a trematode that primarily inhabits the lung parenchyma of humans. Infection occurs via the ingestion of undercooked **crustaceans (crabs or crayfish)** containing metacercariae. Once ingested, the larvae excyst in the duodenum, penetrate the intestinal wall, migrate through the diaphragm, and settle in the lungs, where they mature into adults and induce inflammatory cysts. **Analysis of Incorrect Options:** * **Echinococcus granulosus (Option A):** A cestode (tapeworm) that causes **Hydatid cyst disease**. While it can affect the lungs, its primary site of infection is the liver. It is not classified as a "fluke" (trematode). * **Trichinella spiralis (Option C):** A nematode (roundworm) known for causing trichinosis. Its larvae typically encyst in **striated muscle**; it does not inhabit the lungs as a primary site. * **Fasciola hepatica (Option D):** Known as the **Sheep liver fluke**. It resides in the bile ducts of the liver, not the lungs. **NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Paragonimiasis often mimics **Pulmonary Tuberculosis**, presenting with chronic cough and "rusty sputum" (containing eggs and blood). * **Intermediate Hosts:** 1st host is the Snail; 2nd host is the Crab/Crayfish. * **Diagnosis:** Identification of operculated eggs in sputum or feces. * **Drug of Choice:** Praziquantel.

Question 628: Saturated salt solution concentrates the eggs of which of the following parasites, except?

A. Unfertilized egg of Ascaris (Correct Answer)
B. Trichuris
C. Hymenolepis nana
D. Echinococcus granulosus

Explanation: **Explanation:** The question tests your knowledge of the **Salt Floatation Technique** (Willis Method), a common concentration method used in stool microscopy. This technique relies on the principle of **specific gravity**. **1. Why Unfertilized Ascaris Eggs are the Correct Answer:** The saturated salt solution has a specific gravity of approximately **1.200**. For an egg to float to the surface, its specific gravity must be lower than that of the solution. * **Unfertilized eggs of *Ascaris lumbricoides*** are heavier and denser than the solution (specific gravity >1.200) because they contain a heavy yolk and a thick, often mammillated shell. Therefore, they **sink** rather than float, making this method ineffective for their concentration. **2. Analysis of Incorrect Options:** * **Trichuris trichiura (B):** These eggs have a specific gravity of ~1.150. Since this is lower than 1.200, they float and are easily concentrated. * **Hymenolepis nana (C):** These are light eggs (specific gravity ~1.060) and float readily in salt solution. * **Echinococcus granulosus (D):** While the adult lives in dogs, the eggs (oncospheres) are morphologically similar to *Taenia* eggs. While *Taenia* eggs are borderline heavy, in the context of standard NEET-PG patterns, the **Unfertilized Ascaris egg** is the classic, most cited exception to the floatation method. **3. Clinical Pearls for NEET-PG:** * **The "Exceptions" List:** Saturated salt solution fails to concentrate: 1. **Unfertilized Ascaris eggs** (Too heavy). 2. **Taenia eggs** (Often too heavy/variable). 3. **Operculated eggs** (e.g., *Fasciola*, *Diphyllobothrium*—the salt enters the operculum, making them heavy). 4. **Larvae** (e.g., *Strongyloides*). * **High-Yield Fact:** For heavy eggs and larvae, the **Sedimentation Technique** (Formal-Ether) is preferred as it concentrates all eggs, cysts, and larvae by settling them at the bottom.

Question 629: Which larva is typically found encysted in muscle tissue?

A. Trichinella spiralis (Correct Answer)
B. Ancylostoma duodenale
C. Trichuris trichura
D. Enterobius vermicularis

Explanation: **Explanation:** **1. Why Trichinella spiralis is correct:** *Trichinella spiralis* is the causative agent of Trichinellosis. Its unique life cycle involves the same individual acting as both the definitive and intermediate host. After ingestion of undercooked meat (usually pork) containing **encysted larvae**, the larvae mature in the small intestine. The fertilized females then release newborn larvae that migrate via the bloodstream to reach highly oxygenated **striated skeletal muscles** (e.g., diaphragm, extraocular muscles, deltoid). Here, they penetrate individual muscle fibers and transform into the characteristic **"nurse cells,"** where they remain encysted and viable for years. **2. Why the other options are incorrect:** * **Ancylostoma duodenale (Hookworm):** The infective stage is the filariform larva which penetrates the skin. While it migrates through the lungs, the adult worms reside in the small intestine, attaching to the mucosa to suck blood. They do not encyst in muscle. * **Trichuris trichura (Whipworm):** This parasite has no tissue migratory phase. Eggs are ingested, hatch in the small intestine, and adults reside in the caecum and ascending colon. * **Enterobius vermicularis (Pinworm):** This is a "non-invasive" nematode. The life cycle is limited to the gastrointestinal tract (caecum and perianal skin); there is no larval migration to muscle tissue. **3. NEET-PG High-Yield Pearls:** * **Diagnosis:** Muscle biopsy showing encysted larvae is the gold standard. * **Clinical Triad:** Periorbital edema, myalgia, and eosinophilia. * **Key Lab Finding:** Marked **Eosinophilia** and elevated **CPK** (Creatine Phosphokinase) due to muscle damage. * **Treatment:** Albendazole or Mebendazole are the drugs of choice.

Question 630: In the transmission of malaria, what stage is transferred by a mosquito bite?

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

Explanation: ### Explanation **Correct Answer: A. Sporozoite** **Reasoning:** The life cycle of *Plasmodium* involves two hosts: the female Anopheles mosquito (definitive host) and the human (intermediate host). When an infected mosquito bites a human, it injects **sporozoites** present in its salivary glands into the bloodstream. This is the **infective stage for humans**. These sporozoites travel to the liver within 30 minutes to initiate the exo-erythrocytic cycle. **Analysis of Incorrect Options:** * **B. Merozoite:** These are formed after the rupture of liver schizonts (exo-erythrocytic) or red blood cells (erythrocytic). They are responsible for infecting new RBCs but are not the stage introduced by the mosquito. * **C. Hypnozoite:** This is a **dormant stage** found only in *P. vivax* and *P. ovale* infections. They remain latent in the liver and are responsible for clinical **relapses** months or years later. * **D. Gametocyte:** This is the sexual stage of the parasite formed in human RBCs. While they circulate in human blood, they are the **infective stage for the mosquito**. The mosquito ingests them 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. * **Exo-erythrocytic stage is absent in:** *P. falciparum* (it does not have a persistent liver phase/hypnozoites, hence no relapses). * **Recrudescence vs. Relapse:** Recrudescence (seen in *P. falciparum*) is due to persistent low-level parasitemia in the blood; Relapse (seen in *P. vivax/ovale*) is due to the reactivation of hypnozoites in the liver. * **Drug of choice for Hypnozoites:** Primaquine (contraindicated in G6PD deficiency).

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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