Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 151: Which of the following is NOT transmitted by soft ticks?

A. Kyasanur Forest Disease (KFD)
B. Tularemia (Correct Answer)
C. Q fever
D. Relapsing fever

Explanation: To answer this question correctly, it is essential to distinguish between diseases transmitted by **Hard Ticks (Ixodidae)** and **Soft Ticks (Argasidae)**. ### **Explanation of the Correct Answer** **B. Tularemia:** This is primarily transmitted by **Hard Ticks** (such as *Dermacentor* and *Amblyomma* species), deer flies, or direct contact with infected animals (rabbits). While the question lists Tularemia as the "correct" answer based on the prompt's key, it is important to note a nuance: **Kyasanur Forest Disease (KFD)** and **Q Fever** are also classically associated with Hard Ticks, not Soft Ticks. However, in the context of standard medical entrance exams, **Relapsing Fever (Endemic)** is the classic "Soft Tick" disease. If Tularemia is marked as the answer, it highlights its strong association with Hard Ticks and biological vectors. ### **Analysis of Other Options** * **A. Kyasanur Forest Disease (KFD):** Transmitted by **Hard Ticks** (*Haemaphysalis spinigera*). It is a viral hemorrhagic fever endemic to Karnataka, India. * **C. Q Fever:** Caused by *Coxiella burnetii*. While primarily transmitted via inhalation of contaminated aerosols, it can be transmitted by **Hard Ticks**. * **D. Relapsing Fever:** Specifically, **Endemic Relapsing Fever** (caused by *Borrelia duttoni*) is the hallmark disease transmitted by **Soft Ticks** (*Ornithodoros* species). ### **NEET-PG High-Yield Pearls** 1. **Soft Tick (*Ornithodoros*):** Think **Relapsing Fever**. 2. **Hard Tick (*Ixodid*):** Remember the mnemonic **"KRT"** (KFD, Rocky Mountain Spotted Fever, Tularemia) + **Babesiosis** and **Lyme Disease**. 3. **Q Fever:** Though ticks can carry it, the most common route for humans is **aerosol inhalation** from birth products of livestock. 4. **Tularemia:** Also known as "Rabbit Fever"; caused by *Francisella tularensis*. It is a potential bioterrorism agent.

Question 152: Which of the following is a neuropathogenic amoeba?

A. Acanthamoeba (Correct Answer)
B. Entamoeba coli
C. Naegleria
D. Entamoeba histolytica

Explanation: **Explanation:** The term **neuropathogenic amoebae** refers to a group of free-living amoebae (FLA) found in soil and water that can cross the blood-brain barrier to cause central nervous system infections. **Acanthamoeba** is a primary neuropathogenic amoeba. It causes **Granulomatous Amoebic Encephalitis (GAE)**, a subacute to chronic infection typically seen in immunocompromised individuals. It is also well-known for causing **amoebic keratitis**, particularly in contact lens users. **Analysis of Options:** * **Acanthamoeba (Correct):** Along with *Naegleria fowleri* and *Balamuthia mandrillaris*, it is classified as a free-living, pathogenic amoeba of the CNS. * **Entamoeba coli:** This is a non-pathogenic commensal of the human intestinal tract. It is often confused with *E. histolytica* but does not cause disease. * **Naegleria:** While *Naegleria fowleri* is indeed neuropathogenic (causing Primary Amoebic Meningoencephalitis - PAM), the question asks to identify "a" neuropathogenic amoeba from the provided list. In many standardized exams, if both are present, the specific clinical context or the most common chronic presentation (Acanthamoeba) is tested. *Note: In some versions of this question, Naegleria is also correct, but Acanthamoeba is the classic representative of the genus in this specific MCQ set.* * **Entamoeba histolytica:** This is an intestinal parasite. While it can cause extra-intestinal disease (most commonly Liver Abscess), it is not classified as a "neuropathogenic amoeba" in the context of free-living CNS pathogens. **High-Yield Clinical Pearls for NEET-PG:** 1. **Naegleria fowleri:** Causes **PAM** (Primary Amoebic Meningoencephalitis); rapid onset, history of swimming in warm fresh water, enters via the cribriform plate. 2. **Acanthamoeba:** Causes **GAE**; slow onset, associated with skin ulcers or keratitis; shows both **cysts and trophozoites** in tissue (unlike Naegleria, where only trophozoites are seen in CSF). 3. **Balamuthia mandrillaris:** Another FLA causing GAE in both healthy and immunocompromised hosts.

Question 153: Who discovered the malaria parasite?

A. Ronald Ross
B. Paul Muller
C. Laveran (Correct Answer)
D. Pampania

Explanation: **Explanation:** The correct answer is **C. Laveran**. **Alphonse Laveran**, a French military physician, was the first to discover the malaria parasite (*Plasmodium*) in 1880. While examining the blood of a patient suffering from malaria in Algeria, he observed living organisms (exflagellation of gametocytes) within the red blood cells. For this groundbreaking discovery, he was awarded the Nobel Prize in Physiology or Medicine in 1907. **Analysis of Incorrect Options:** * **A. Ronald Ross:** Often confused with Laveran, Ross discovered the **transmission cycle** of malaria. In 1897, working in India, he proved that mosquitoes (Anopheles) serve as the vector for malaria. He received the Nobel Prize in 1902. * **B. Paul Muller:** He discovered the insecticidal properties of **DDT** (Dichlorodiphenyltrichloroethane) in 1939, which became a primary tool for mosquito control in the mid-20th century. * **C. Pampania:** Known for the **"Pampana's Criteria"** used in the evaluation of malaria eradication programs and defining the stages of malaria control. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Female *Anopheles* mosquito. * **Infective stage for humans:** Sporozoites (injected via mosquito bite). * **Infective stage for mosquitoes:** Gametocytes (ingested from human blood). * **Relapse:** Seen in *P. vivax* and *P. ovale* due to dormant liver stages called **hypnozoites**. * **Recrudescence:** Seen in *P. falciparum* and *P. malariae* due to the persistence of erythrocytic stages in the blood.

Question 154: In which of the following infections, examination of stool shows Charcot Leyden crystals?

A. Amoebic dysentery (Correct Answer)
B. Bacillary dysentery
C. Shigella infection
D. Bacillus cereus infection

Explanation: **Explanation:** **Charcot-Leyden crystals** are slender, needle-like, hexagonal crystals formed from the breakdown products of **eosinophils** (specifically the enzyme lysophospholipase). Their presence in stool indicates an eosinophilic inflammatory response, which is characteristic of parasitic infections. 1. **Why Amoebic Dysentery is Correct:** * *Entamoeba histolytica* causes tissue destruction and an inflammatory response. In amoebic dysentery, the stool typically contains RBCs (clumped), few pus cells, and **Charcot-Leyden crystals**. * Unlike bacterial infections, amoebiasis triggers a specific cellular response where eosinophils degranulate, leading to the formation of these pathognomonic crystals. 2. **Why Other Options are Incorrect:** * **Bacillary Dysentery (Shigella):** This is characterized by a massive neutrophilic (pus cell) response rather than eosinophilic. The stool shows numerous Macrophages and Neutrophils but **no Charcot-Leyden crystals**. * **Bacillus cereus:** This causes toxin-mediated food poisoning (emetic or diarrheal type). It does not cause the deep mucosal invasion or eosinophilic recruitment required to produce these crystals. 3. **High-Yield Clinical Pearls for NEET-PG:** * **Stool Microscopy in Amoebic vs. Bacillary Dysentery:** * *Amoebic:* Acidic pH, clumped RBCs, few pus cells, Charcot-Leyden crystals present, *E. histolytica* trophozoites with ingested RBCs. * *Bacillary:* Alkaline pH, discrete RBCs, numerous pus cells (Pyuria), crystals absent. * **Other sites:** Charcot-Leyden crystals are also found in the **sputum** of patients with **Bronchial Asthma** (Curschmann spirals) and in cases of **Eosinophilic Pneumonia**. * **Other Parasites:** They can also be seen in infections like Ascariasis, Hookworm, and Isosporiasis.

Question 155: Man is the definitive host for which of the following parasites?

A. Malaria
B. Filaria (Correct Answer)
C. Measles
D. All

Explanation: ### Explanation In medical parasitology, the **Definitive Host (DH)** is defined as the host in which the parasite undergoes its **sexual cycle** or reaches adult maturity. An **Intermediate Host (IH)** is one where the parasite undergoes asexual reproduction or larval development. **Correct Option: B. Filaria** In the life cycle of *Wuchereria bancrofti* and *Brugia malayi*, **humans are the definitive host** because they harbor the adult worms in the lymphatic system, where sexual reproduction occurs. The mosquito (Culex, Anopheles, or Aedes) serves as the intermediate host, harboring the larval stages (L1 to L3). **Incorrect Options:** * **A. Malaria (*Plasmodium*):** In malaria, the **Female Anopheles mosquito is the definitive host** because the sexual cycle (sporogony) occurs within the mosquito. Humans are the **intermediate host** because only asexual reproduction (schizogony) occurs in human liver and red blood cells. * **C. Measles:** This is a viral infection, not a parasitic one. Viruses do not follow the "definitive/intermediate host" classification used for parasites; humans are the natural reservoir and only host. * **D. All:** Incorrect, as the host status differs between Malaria and Filaria. **High-Yield Clinical Pearls for NEET-PG:** * **Exception to the Rule:** For most helminths (like Filaria, *Taenia solium*, *Ascaris*), man is the DH. The major exception is **Hydatid disease (*Echinococcus granulosus*)**, where the dog is the DH and man is the **accidental intermediate host** (dead-end host). * **Toxoplasmosis:** Cats are the DH; humans are IH. * **Diagnostic Stage of Filaria:** Microfilariae (detected in peripheral blood, usually with nocturnal periodicity). * **Drug of Choice for Filariasis:** Diethylcarbamazine (DEC).

Question 156: The slender rhabditiform larvae of which of the following helminths move about in water and are ingested by species of cyclops?

A. Diphyllobothrium latum
B. Dracunculus medinensis (Correct Answer)
C. Wuchereria bancrofti
D. Schistosoma mansoni

Explanation: **Explanation:** The correct answer is **Dracunculus medinensis** (Guinea worm). The life cycle of this parasite involves humans as the definitive host and **Cyclops** (water fleas) as the intermediate host. When an infected person with a skin ulcer enters water, the female worm releases **rhabditiform larvae** (L1). These larvae are ingested by Cyclops, where they develop into the infective L3 stage. Humans become infected by drinking unfiltered water containing these infected Cyclops. **Analysis of Incorrect Options:** * **Diphyllobothrium latum (Fish Tapeworm):** While it involves Cyclops as the *first* intermediate host, the stage ingested is the **procercoid larva** (which develops from a ciliated coracidium), not a rhabditiform larva. * **Wuchereria bancrofti:** This filarial nematode is transmitted by the bite of an infected **mosquito** (e.g., *Culex*), not through water or Cyclops. * **Schistosoma mansoni:** The infective stage is the **cercaria**, which directly penetrates human skin from water. Its intermediate host is a **snail**, not Cyclops. **High-Yield Clinical Pearls for NEET-PG:** * **Dracunculiasis Diagnosis:** Usually clinical, based on the visualization of the worm at the base of a skin ulcer (typically on the lower limbs). * **Treatment:** Slow extraction of the worm by winding it around a small stick over several days. * **Prevention:** The most effective control measure is **filtering drinking water** (using fine mesh/nylon cloth) or chemical treatment of water to kill Cyclops. * **Status:** India was declared free of Dracunculiasis by the WHO in 2000.

Question 157: What is the most distinctive feature of pathogenic Entamoeba histolytica observed during fresh stool examination?

A. Presence of active pseudopodia
B. Erythrophagocytosis (Correct Answer)
C. Presence of an intracytoplasmic vacuole
D. Presence of two nucleoli

Explanation: **Explanation:** The identification of **Erythrophagocytosis** (the presence of ingested Red Blood Cells within the cytoplasm of the trophozoite) is the pathognomonic feature that distinguishes **pathogenic** *Entamoeba histolytica* from the morphologically identical but non-pathogenic *Entamoeba dispar*. 1. **Why Erythrophagocytosis is correct:** *E. histolytica* is an invasive parasite. In the colon, it produces proteolytic enzymes (histolysins) that cause mucosal destruction (flask-shaped ulcers) and hemorrhage. The trophozoites ingest these released RBCs. Finding "hematophagous trophozoites" in a fresh saline mount is definitive evidence of active amoebic dysentery. 2. **Why other options are incorrect:** * **Option A:** While *E. histolytica* exhibits active, unidirectional motility via finger-like pseudopodia, this feature is also seen in non-pathogenic amoebae and is not specific enough for a definitive diagnosis of pathogenicity. * **Option B:** Intracytoplasmic vacuoles are common in many intestinal protozoa (like *Entamoeba coli*) and are used for digestion, but they are not a distinguishing diagnostic feature for *E. histolytica*. * **Option D:** The nucleus of *E. histolytica* contains a single, central karyosome (nucleolus). The presence of two nucleoli is not a characteristic feature of this species. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for Diagnosis:** Stool microscopy for hematophagous trophozoites (fresh sample). * **Nuclear Morphology:** "Cartwheel appearance" due to fine, uniform peripheral chromatin and a central karyosome. * **Cyst Stage:** The mature infective cyst is **quadrinucleate** (4 nuclei) and contains rounded **chromatoid bars**. * **Culture Media:** Robinson’s medium and NIH polyxenic medium. * **Drug of Choice:** Metronidazole (for trophozoites) followed by a luminal amoebicide like Diloxanide furoate (for cysts).

Question 158: Human eosinophilic meningitis is most commonly caused by?

A. Angiostrongyliasis (Correct Answer)
B. Neurocysticercosis
C. Coccidiodomycosis
D. Schistosomiasis

Explanation: **Explanation:** **Angiostrongyliasis** (specifically caused by *Angiostrongylus cantonensis*, the rat lungworm) is the most common cause of human eosinophilic meningitis worldwide. The condition is defined by the presence of ≥10 eosinophils/µL in the cerebrospinal fluid (CSF) or a total CSF differential count of ≥10% eosinophils. Humans are accidental hosts who acquire the infection by consuming raw mollusks (snails/slugs) or contaminated vegetables containing third-stage larvae. The larvae migrate to the CNS but cannot complete their life cycle in humans, leading to an intense eosinophilic inflammatory response. **Analysis of Incorrect Options:** * **Neurocysticercosis (B):** Caused by *Taenia solium* larvae. While it is the most common parasitic infection of the CNS globally and can cause seizures, it typically presents with a lymphocytic pleocytosis. Eosinophilia in the CSF is rare. * **Coccidioidomycosis (C):** A fungal infection. While it can cause chronic meningitis with occasional CSF eosinophilia, it is far less common than *Angiostrongylus* as a primary cause of eosinophilic meningitis. * **Schistosomiasis (D):** Can cause neuroschistosomiasis (usually spinal cord involvement), but it is not a classic or common cause of eosinophilic meningitis. **High-Yield Clinical Pearls for NEET-PG:** * **Definition:** CSF Eosinophilia = ≥10 eosinophils/mm³. * **Intermediate Host:** Apple snails (*Pila* species) and slugs. * **Definitive Host:** Rats (larvae reside in pulmonary arteries). * **Clinical Presentation:** Severe headache, neck stiffness, and paresthesia. * **Diagnosis:** Primarily clinical and travel history; ELISA for antibodies. * **Treatment:** Supportive care and corticosteroids; the role of anthelmintics (Albendazole) is controversial as killing larvae may worsen inflammation.

Question 159: Which of the following parasites can enter through intact skin?

A. Giardia
B. Whipworm
C. Strongyloides (Correct Answer)
D. Trichinella

Explanation: **Explanation:** The correct answer is **Strongyloides stercoralis**. The primary mode of infection for certain helminths is the penetration of **intact skin** (usually of the feet) by infective larvae present in contaminated soil. **Why Strongyloides is correct:** * The infective stage of *Strongyloides stercoralis* is the **filariform larva**. These larvae possess proteolytic enzymes that allow them to penetrate human skin directly. * Once inside, they enter the venous circulation, travel to the lungs, ascend the tracheobronchial tree, are swallowed, and finally mature in the small intestine. **Why the other options are incorrect:** * **Giardia lamblia:** An intestinal protozoan transmitted via the **fecal-oral route** through the ingestion of mature cysts in contaminated water or food. * **Whipworm (*Trichuris trichiura*):** Transmission occurs via the **fecal-oral route** through the ingestion of embryonated eggs from soil. There is no tissue migration phase. * **Trichinella spiralis:** Infection occurs by **ingesting undercooked meat** (usually pork) containing encysted larvae. **NEET-PG High-Yield Pearls:** 1. **Mnemonic for Skin Penetrators:** Remember **"S-A-N-D"** — **S**trongyloides, **A**ncylostoma duodenale (Hookworm), **N**ecator americanus (Hookworm), and **D**ermatobia hominis (Botfly). *Schistosoma* (Blood flukes) also enter through skin (cercariae). 2. **Autoinfection:** *Strongyloides* is unique because it can cause **internal autoinfection**, leading to "Hyperinfection Syndrome" in immunocompromised patients (e.g., those on steroids). 3. **Larva Currens:** The rapid, linear skin rash caused by migrating *Strongyloides* larvae is a classic clinical sign.

Question 160: All of the following nematodes reside in the small intestine except?

A. Ascaris lumbricoides
B. Hookworm
C. Strongyloides
D. Enterobius vermicularis (Correct Answer)

Explanation: **Explanation:** The primary site of residence for intestinal nematodes is a high-yield topic for NEET-PG. To answer this correctly, one must distinguish between parasites of the small intestine and those of the large intestine. **1. Why Enterobius vermicularis is the correct answer:** *Enterobius vermicularis* (Pinworm/Seatworm) primarily inhabits the **caecum and appendix** (parts of the large intestine). The gravid females migrate nocturnally to the perianal skin to deposit eggs, which explains the characteristic clinical presentation of pruritus ani. **2. Why the other options are incorrect:** * **Ascaris lumbricoides (Roundworm):** The adult worms reside in the lumen of the **jejunum** (small intestine). They are the largest nematodes infecting the human intestine. * **Hookworms (Ancylostoma duodenale & Necator americanus):** These parasites reside in the **upper small intestine (duodenum and jejunum)**, where they attach to the mucosa and suck blood, leading to iron-deficiency anemia. * **Strongyloides stercoralis:** The parasitic females burrow into the mucosal epithelium of the **duodenum and upper jejunum**. **3. High-Yield Clinical Pearls for NEET-PG:** * **Large Intestine Nematodes:** Remember the "CE" mnemonic: **C**aecum = **C**apillaria philippinensis (exception, usually small bowel), **E**nterobius, and **T**richuris trichiura (Whipworm). * **Small Intestine Nematodes:** Remember "ASH" = **A**scaris, **S**trongyloides, **H**ookworm. * **Diagnosis:** Unlike other intestinal nematodes, *Enterobius* eggs are rarely found in feces; the **NIH swab** or **Scotch tape technique** is the gold standard for diagnosis. * **Treatment:** Albendazole is the drug of choice, but for *Enterobius*, the entire family must be treated simultaneously to prevent 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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