Parasitology — MCQs
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In which location does Schistosoma japonicum reside?
The number of pairs of flagella in the depicted organism is:
A biology graduate student who recently visited a tropical region of Africa presents with new visual impairment and the sensation that something is moving in her eye. She is concerned because she was warned about an eye disease transmitted by black flies. While in Africa, she was in a river area and received numerous black fly bites. She also has some subcutaneous nodules. If her infection was acquired by black fly bite, what is the most likely causative agent?
A 30-year-old farmer, treated initially with chloroquine for uncomplicated malaria, now has an episode of relapse. What could be the reason for relapse?
All of the following are true about Trichinella spiralis EXCEPT?
What is the vector for plague?
Which of the following eggs does not float on a saturated salt solution?
In occult filariasis, where are microfilariae typically found?
All of the following are true regarding Toxoplasmosis, except?
Visceral larva migrans is caused by which of the following organisms?
Parasitology Indian Medical PG Practice Questions and MCQs
Question 221: In which location does Schistosoma japonicum reside?
- A. Vesical Plexus
- B. Splenic Vein (Correct Answer)
- C. Systemic Circulation
- D. Gall bladder
Explanation: **Explanation:** The correct answer is **Splenic Vein**. *Schistosoma japonicum* is a blood fluke that primarily inhabits the **superior mesenteric veins** and their tributaries, which drain the small intestine. However, it is also frequently found in the **splenic vein**. Because *S. japonicum* produces a high volume of eggs that are carried via the portal circulation to the liver, it is the species most commonly associated with severe hepatosplenic disease and portal hypertension. **Analysis of Options:** * **Vesical Plexus (Option A):** This is the characteristic habitat of ***Schistosoma haematobium***. It resides in the venous plexuses of the urinary bladder, leading to hematuria and squamous cell carcinoma of the bladder. * **Systemic Circulation (Option C):** While cercariae travel through the circulation to reach the lungs and liver, the adult worms do not reside here. They specifically inhabit the portal venous system to facilitate egg excretion into the gut or bladder. * **Gall bladder (Option D):** This is not a primary site for Schistosomes. Parasites like *Clonorchis sinensis* or *Fasciola hepatica* are more typically associated with the biliary tract. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat Mnemonic:** * *S. haematobium*: **H**ematobium = **H**ematuria (Vesical plexus). * *S. mansoni*: **M**ansoni = **M**esenteric (Inferior mesenteric vein/Sigmoid colon). * *S. japonicum*: **J**aponicum = **J**ejunum/Superior Mesenteric (also Splenic vein). * **Egg Morphology:** *S. japonicum* eggs are rounded/oval with a **rudimentary lateral knob** (often difficult to see), unlike the prominent terminal spine of *S. haematobium* or the large lateral spine of *S. mansoni*. * **Katayama Fever:** An acute serum sickness-like reaction occurring weeks after infection, most severe in *S. japonicum*.
Question 222: The number of pairs of flagella in the depicted organism is:
- A. 1
- B. 2
- C. 3
- D. 4 (Correct Answer)
Explanation: ***4*** - **Giardia lamblia** trophozoites possess **4 pairs of flagella** (8 flagella total), which is a key diagnostic feature for identification. - The **trophozoite** has a characteristic **pear-shaped** morphology with **two nuclei** giving it a "face-like" appearance under microscopy. *1* - **Leishmania** species have only **1 flagellum** in their promastigote form, not pairs of flagella. - This count is too low for **Giardia lamblia**, which requires multiple flagella for its characteristic tumbling motility. *2* - **Trichomonas vaginalis** has **1 pair of flagella** (4 flagella total) plus an **undulating membrane**. - This number is insufficient for **Giardia**, which needs more flagella for its complex swimming pattern. *3* - No major **flagellated parasite** of clinical significance possesses exactly **3 pairs of flagella**. - This count falls short of **Giardia's** requirement for **4 pairs** to maintain its characteristic motility and adherence mechanisms.
Question 223: A biology graduate student who recently visited a tropical region of Africa presents with new visual impairment and the sensation that something is moving in her eye. She is concerned because she was warned about an eye disease transmitted by black flies. While in Africa, she was in a river area and received numerous black fly bites. She also has some subcutaneous nodules. If her infection was acquired by black fly bite, what is the most likely causative agent?
- A. Ancylostoma braziliense
- B. Trichinella spiralis
- C. Dracunculus medinensis
- D. Onchocerca volvulus (Correct Answer)
Explanation: **Explanation** The correct answer is **D. Onchocerca volvulus**. The clinical presentation describes **Onchocerciasis (River Blindness)**. The diagnosis is confirmed by the classic triad: history of exposure in an endemic region (Africa), transmission via the **Black fly (*Simulium* species)**, and clinical features including subcutaneous nodules (**Onchocercomas**) and visual impairment. The "moving sensation" in the eye refers to the migration of microfilariae into the ocular tissues, leading to sclerosing keratitis—the second leading infectious cause of blindness worldwide. **Why other options are incorrect:** * **A. Ancylostoma braziliense:** Causes Cutaneous Larva Migrans (creeping eruption). It is transmitted by direct skin contact with soil contaminated by hookworm larvae from cats/dogs, not by black flies. * **B. Trichinella spiralis:** Acquired by consuming undercooked meat (pork) containing encysted larvae. It presents with periorbital edema, myalgia, and eosinophilia, but does not involve black fly transmission. * **C. Dracunculus medinensis:** Causes Guinea worm disease. It is transmitted by drinking water containing infected *Cyclops* (copepods). It presents with a painful skin blister, usually on the lower limb, through which the adult worm emerges. **High-Yield NEET-PG Pearls:** * **Vector:** *Simulium* (Black fly) breeds in fast-flowing rivers (hence "River Blindness"). * **Infective stage:** Third-stage larvae (L3). * **Diagnosis:** **Skin snip preparation** to demonstrate microfilariae (they do not have a periodic presence in the blood). * **Treatment:** **Ivermectin** is the drug of choice (kills microfilariae). Doxycycline is used to target *Wolbachia*, an endosymbiont essential for the worm's survival. * **Mazzotti Reaction:** A severe inflammatory response (fever, rash, hypotension) that can occur after treating Onchocerciasis with diethylcarbamazine (DEC).
Question 224: A 30-year-old farmer, treated initially with chloroquine for uncomplicated malaria, now has an episode of relapse. What could be the reason for relapse?
- A. P. vivax has a significant level of chloroquine resistance.
- B. P. vivax has a persistent exoerythrocytic stage (hypnozoite). (Correct Answer)
- C. P. vivax has a persistent erythrocytic stage.
- D. Chloroquine is not one of the drugs of choice.
Explanation: ### Explanation **Correct Answer: B. P. vivax has a persistent exoerythrocytic stage (hypnozoite).** **1. Why Option B is Correct:** The term **"Relapse"** in malaria is specifically associated with *Plasmodium vivax* and *Plasmodium ovale*. These species possess a unique dormant stage in the life cycle known as the **hypnozoite**, which persists in the liver (exoerythrocytic stage) after the initial infection. While Chloroquine effectively kills the erythrocytic (blood) stages to treat the acute attack, it has no effect on hypnozoites. These dormant forms can reactivate weeks or months later, leading to a new bout of erythrocytic infection, termed a relapse. **2. Why Other Options are Incorrect:** * **Option A:** While chloroquine resistance is emerging in some regions, it typically leads to **treatment failure** (recrudescence), not the biological phenomenon of relapse. * **Option C:** A persistent erythrocytic stage leads to **Recrudescence** (seen in *P. falciparum* due to inadequate treatment or resistance), not relapse. Relapse always originates from the liver. * **Option D:** Chloroquine remains the **drug of choice** for chloroquine-sensitive *P. vivax* malaria. The issue is not the drug's efficacy against blood stages, but its inability to clear the liver reservoir. **3. NEET-PG High-Yield Pearls:** * **Radical Cure:** To prevent relapse in *P. vivax/ovale*, **Primaquine** (or Tafenoquine) must be administered for 14 days to kill the hypnozoites. * **G6PD Screening:** Always screen for G6PD deficiency before starting Primaquine to avoid drug-induced **hemolysis**. * **Recrudescence vs. Relapse:** * *Recrudescence:* Survival of erythrocytic parasites (All species, mainly *P. falciparum*). * *Relapse:* Reactivation of hypnozoites in the liver (*P. vivax* and *P. ovale* only). * **Shortest Incubation Period:** *P. falciparum* (~12 days); **Longest:** *P. malariae* (~28 days).
Question 225: All of the following are true about Trichinella spiralis EXCEPT?
- A. Man is an accidental host and acts as a dead-end.
- B. Transmitted by ingestion of raw or undercooked pork.
- C. Most common muscle involved is extraocular muscles.
- D. Fairey's test is the intradermal test done. (Correct Answer)
Explanation: **Explanation:** *Trichinella spiralis* is a tissue nematode that causes Trichinellosis. Understanding its unique life cycle and diagnostic tests is crucial for NEET-PG. **Why Option D is the Correct Answer (The "Except" statement):** The intradermal test used for the diagnosis of Trichinellosis is the **Bachman intradermal test**, not Fairey’s test. **Fairey’s test** is an intradermal test historically associated with **Schistosomiasis**. Therefore, statement D is factually incorrect regarding *Trichinella*. **Analysis of Other Options:** * **Option A:** Humans are indeed **accidental hosts**. While both the adult and larval stages occur in the same host, humans act as a **dead-end** because the larvae encysted in human muscle are unlikely to be consumed by another host. * **Option B:** The primary mode of transmission is the **ingestion of raw or undercooked meat** (most commonly pork) containing the infective encysted larvae. * **Option C:** Larvae have a predilection for highly active muscles with high oxygen content. The **extraocular muscles** are the most frequently involved, followed by the tongue, diaphragm, and intercostal muscles. **Clinical Pearls for NEET-PG:** * **Clinical Triad:** Look for a history of pork ingestion followed by **fever, periorbital edema, and myalgia**. * **Lab Findings:** Marked **Eosinophilia** and elevated **Creatine Phosphokinase (CPK)** due to muscle damage. * **Diagnosis:** Muscle biopsy (showing coiled larvae) is the gold standard. * **Treatment:** Albendazole or Mebendazole are the drugs of choice.
Question 226: What is the vector for plague?
- A. Pediculus humanus
- B. Xenopsylla cheopis (Correct Answer)
- C. Ixodid daminii
- D. Haemaphysalis spinigera
Explanation: **Explanation:** Plague is a zoonotic infection caused by the bacterium **Yersinia pestis**. The correct answer is **Xenopsylla cheopis** (the Oriental rat flea), which serves as the primary vector. 1. **Why Xenopsylla cheopis is correct:** The transmission cycle involves the flea feeding on an infected rodent (the reservoir). The bacteria multiply in the flea's proventriculus, forming a biofilm that causes a "blockage." When the "blocked flea" attempts to feed on a human, it regurgitates the bacteria into the host's bloodstream, leading to Bubonic plague. 2. **Analysis of Incorrect Options:** * **Pediculus humanus (Human Louse):** The vector for Epidemic Typhus (*Rickettsia prowazekii*), Relapsing Fever (*Borrelia recurrentis*), and Trench Fever (*Bartonella quintana*). * **Ixodes dammini (now Ixodes scapularis):** The hard tick vector for Lyme disease (*Borrelia burgdorferi*) and Babesiosis. * **Haemaphysalis spinigera:** The primary tick vector for Kyasanur Forest Disease (KFD), a viral hemorrhagic fever found in India. **High-Yield Clinical Pearls for NEET-PG:** * **Reservoirs:** The wild rodent reservoir is *Tatera indica* (Indian gerbil), while the urban reservoir is *Rattus rattus*. * **Flea Index:** A "General Flea Index" of **>1** is considered a danger signal for a potential plague outbreak. * **Diagnosis:** Safety-pin appearance (bi-polar staining) on Wayson or Giemsa stain. * **Drug of Choice:** Streptomycin is traditionally the drug of choice; Doxycycline is used for prophylaxis.
Question 227: Which of the following eggs does not float on a saturated salt solution?
- A. Fertilized egg of Ascaris
- B. Trichuris trichura
- C. H. Nana
- D. Unfertilized egg of Ascaris (Correct Answer)
Explanation: ### Explanation The ability of parasitic eggs to float in a saturated salt solution (Specific Gravity **1.200**) depends on the principle of **differential density**. Eggs with a specific gravity lower than 1.200 will float, while those that are heavier will sink. **Why Unfertilized Ascaris Eggs do not float:** The **Unfertilized egg of *Ascaris lumbricoides*** is the heaviest among common helminth eggs. It has a specific gravity greater than 1.200 because it is relatively large, elongated, and contains a heavy, disorganized mass of yolk granules. Due to this high density, it settles at the bottom, making the **Salt Flotation Technique** (Willis technique) ineffective for its detection. Sedimentation methods are required instead. **Analysis of Incorrect Options:** * **Fertilized egg of *Ascaris*:** These are rounded, possess a thick shell, and have a specific gravity of approximately **1.050**. Being lighter than the salt solution, they float readily. * **Trichuris trichiura:** Despite their "barrel shape" and polar plugs, these eggs have a specific gravity lower than 1.200 and will float. * **Hymenolepis nana (H. Nana):** These are thin-shelled, lightweight eggs that float easily in saturated salt solutions. **High-Yield Clinical Pearls for NEET-PG:** * **Non-floating eggs (Mnemonic: "OUT"):** **O**perculated eggs (e.g., *Trematodes* like *Fasciola*), **U**nfertilized *Ascaris* eggs, and **T**aenia eggs (variable/heavy). * **Saturated Salt Solution:** The most common reagent used is Sodium Chloride (NaCl). * **Ascaris lumbricoides:** Known as the "Roundworm," it is the most common helminthic infection worldwide. Remember the "Loeffler’s Syndrome" (pulmonary phase) associated with its larval migration.
Question 228: In occult filariasis, where are microfilariae typically found?
- A. Peripheral blood
- B. Peripheral lymph nodes
- C. Deep lymph nodes
- D. None of the above (Correct Answer)
Explanation: ### Explanation **Concept Overview:** Occult filariasis (also known as **Meyers-Kouwenaar syndrome**) is a hypersensitivity reaction to the antigens of microfilariae (*Wuchereria bancrofti* or *Brugia malayi*). Unlike classical filariasis, the hallmark of this condition is the **absence of microfilariae in the peripheral blood**. **Why "None of the above" is correct:** In occult filariasis, the body develops an intense immunological response (Type I and Type IV hypersensitivity). This leads to the rapid destruction and trapping of microfilariae within the **visceral organs**, specifically the **lungs, liver, and spleen**. They are not typically found in the peripheral blood or lymph nodes; instead, they are sequestered in the tissues where they form eosinophilic granulomas known as **Meyers-Kouwenaar bodies**. **Analysis of Incorrect Options:** * **A. Peripheral blood:** This is the most common site for microfilariae in *classical* filariasis (often showing nocturnal periodicity). In occult filariasis, they are characteristically absent from the blood. * **B & C. Lymph nodes:** While adult worms reside in the lymphatic system in classical filariasis causing elephantiasis, in the occult form, the microfilariae are destroyed in the **visceral parenchyma** (lungs/liver) rather than circulating or residing in the peripheral or deep lymph nodes. **NEET-PG High-Yield Pearls:** * **Tropical Pulmonary Eosinophilia (TPE):** The most common clinical manifestation of occult filariasis, presenting with nocturnal cough, wheezing, and massive eosinophilia. * **Diagnostic Marker:** Characterized by significantly elevated **Serum IgE levels** and high titers of antifilarial antibodies. * **Treatment:** Responds dramatically to **Diethylcarbamazine (DEC)**. * **Pathology:** Look for **Meyers-Kouwenaar bodies** (microfilariae surrounded by eosinophilic material) in lung or liver biopsies.
Question 229: All of the following are true regarding Toxoplasmosis, except?
- A. Subclinical in most adult cases. (Correct Answer)
- B. Intracerebral calcification in children.
- C. IgM antibodies in a newborn suggest congenital infection.
- D. Not infective in the third trimester of pregnancy.
Explanation: **Explanation:** The correct answer is **D (Not infective in the third trimester of pregnancy)**. *Note: The question asks for the "Except" (false statement). While Option A is a true statement, Option D is factually incorrect, making it the right choice for this question.* **1. Why Option D is the correct answer (The False Statement):** Toxoplasmosis can be transmitted to the fetus during **any trimester** of pregnancy. In fact, the risk of transmission is **highest in the third trimester** (approx. 60-80%), although the clinical severity is usually lower. Conversely, transmission in the first trimester is less frequent but results in more severe fetal damage or miscarriage. **2. Analysis of other options:** * **Option A (True):** In immunocompetent adults, *Toxoplasma gondii* infection is **subclinical/asymptomatic** in 80-90% of cases. When symptomatic, it typically presents as self-limiting lymphadenopathy (Piringer-Kuchinka lymphadenitis). * **Option B (True):** Congenital toxoplasmosis is characterized by the classic triad: **Chorioretinitis, Hydrocephalus, and Intracranial calcifications** (typically diffuse, unlike the periventricular calcifications seen in CMV). * **Option C (True):** Maternal IgG crosses the placenta, but **IgM does not**. Therefore, the presence of Toxoplasma-specific IgM in a newborn’s serum is definitive evidence of a congenital infection (fetal antibody production). **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Cat (sheds oocysts in feces). * **Intermediate Host:** Humans and other mammals. * **Infective forms:** Oocysts (from cat feces), Bradyzoites (in undercooked meat), and Tachyzoites (transplacental). * **Diagnosis in AIDS:** Ring-enhancing lesions on CT/MRI (Differential: CNS Lymphoma). * **Drug of Choice:** Pyrimethamine + Sulfadiazine.
Question 230: Visceral larva migrans is caused by which of the following organisms?
- A. Ascariasis
- B. Toxocara Canis (Correct Answer)
- C. Schistosomiasis
- D. Clonorchis Buski
Explanation: **Explanation:** **Visceral Larva Migrans (VLM)** is a clinical syndrome caused by the migration of second-stage larvae of non-human nematodes through the internal organs of humans. **Why Toxocara canis is correct:** *Toxocara canis* (dog roundworm) and *Toxocara cati* (cat roundworm) are the primary causative agents. Humans, typically children, are accidental hosts who ingest embryonated eggs from soil contaminated with animal feces. Because humans are "dead-end" hosts, the larvae cannot complete their life cycle to become adult worms in the intestine. Instead, they penetrate the intestinal wall and migrate through the liver, lungs, and eyes, triggering a robust inflammatory response and peripheral **hypereosinophilia**. **Why the other options are incorrect:** * **A. Ascariasis:** *Ascaris lumbricoides* is a human parasite. While its larvae do migrate through the lungs (causing Löffler’s syndrome), they eventually return to the intestine to mature into adult worms. VLM specifically refers to larvae that cannot mature in humans. * **C. Schistosomiasis:** This is caused by blood flukes (trematodes). The pathology is primarily due to eggs trapped in tissues (causing granulomas) rather than wandering larval stages in the viscera. * **D. Clonorchis sinensis:** (Note: *Clonorchis buski* is a misnomer; *Fasciolopsis buski* is the giant intestinal fluke). *Clonorchis* is the Chinese liver fluke, which resides in the biliary tract, not as migrating larvae in the systemic circulation. **High-Yield Clinical Pearls for NEET-PG:** * **Ocular Larva Migrans (OLM):** When *Toxocara* larvae migrate to the eye, it can mimic retinoblastoma. * **Diagnosis:** Characterized by high persistent eosinophilia, hepatomegaly, and positive ELISA for *Toxocara* antigens. Stool examination is **useless** because the worms never reach maturity in the human gut. * **Cutaneous Larva Migrans (CLM):** Primarily caused by *Ancylostoma braziliense* (dog/cat hookworm).
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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