Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 191: What is the vector for Kala-azar?

A. Flea
B. Tsetse fly
C. Sand fly (Correct Answer)
D. Tick

Explanation: **Explanation:** **Kala-azar (Visceral Leishmaniasis)** is caused by the protozoan parasite *Leishmania donovani*. The correct answer is the **Sand fly** (specifically *Phlebotomus argentipes* in India). 1. **Why Sand fly is correct:** The sand fly acts as the biological vector. When it bites an infected human, it ingests macrophages containing **amastigotes**. Inside the sand fly’s midgut, these transform into flagellated **promastigotes** (the infective stage), which are then transmitted to a new host during a subsequent blood meal. 2. **Why other options are incorrect:** * **Flea:** Primarily the vector for *Yersinia pestis* (Plague) and *Rickettsia typhi* (Endemic typhus). * **Tsetse fly:** The vector for *Trypanosoma brucei*, causing African Sleeping Sickness. * **Tick:** Vectors for diseases like Rickettsial fever (Rocky Mountain Spotted Fever), Babesiosis, and Lyme disease. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Form:** Promastigote (found in the vector). * **Diagnostic Form:** Amastigote (LD bodies) found in the Reticuloendothelial system (Spleen, Bone marrow, Liver). * **Gold Standard Diagnosis:** Splenic aspiration (highest yield) or Bone marrow biopsy showing LD bodies. * **Drug of Choice:** Liposomal Amphotericin B is currently the preferred treatment. * **Post-Kala-azar Dermal Leishmaniasis (PKDL):** A non-ulcerative cutaneous lesion appearing years after "cured" visceral leishmaniasis, acting as a reservoir for the parasite.

Question 192: Autoinfection is NOT seen in which of the following?

A. Hymenolepis nana
B. Hymenolepis diminuta (Correct Answer)
C. Strongyloidosis
D. Taenia solium

Explanation: **Explanation:** The concept of **autoinfection** refers to the ability of a parasite to complete its life cycle and multiply within a single host without the need for an external environment or an intermediate host for reinfection. **Why Hymenolepis diminuta is the correct answer:** Unlike *H. nana*, **Hymenolepis diminuta (Rat Tapeworm)** is an obligatory indirect parasite. It requires an **intermediate host** (usually an arthropod like a grain beetle or flea) to develop from an egg into a cysticercoid larva. Humans are infected only by ingesting the infected insect. Because the eggs passed in feces are not immediately infective to humans, autoinfection cannot occur. **Analysis of incorrect options:** * **Hymenolepis nana (Dwarf Tapeworm):** This is the most common cause of autoinfection in helminths. Eggs can hatch within the intestine (internal autoinfection) or be transferred from anus to mouth via fingers (external autoinfection). It is unique because it does not strictly require an intermediate host. * **Strongyloides stercoralis:** Known for **internal autoinfection**, where rhabditiform larvae transform into filariform larvae within the gut and penetrate the perianal skin or intestinal mucosa, leading to chronic infection and hyperinfection syndrome. * **Taenia solium (Pork Tapeworm):** Can cause autoinfection leading to **Cysticercosis**. If a person harboring the adult worm ingests eggs (via contaminated hands or reverse peristalsis), the larvae hatch and migrate to tissues (brain, muscles). **NEET-PG High-Yield Pearls:** * **Parasites showing Autoinfection:** *H. nana, Strongyloides stercoralis, Taenia solium, Enterobius vermicularis,* and *Cryptosporidium parvum*. * **H. nana** is the smallest cestode infecting humans and the only one that can complete its life cycle without an intermediate host. * **Hyperinfection syndrome** in immunocompromised patients (e.g., those on steroids) is a classic complication of *Strongyloides* autoinfection.

Question 193: Which virulence factor aids Entamoeba histolytica in adhering to the intestinal mucosa?

A. Lectin (Correct Answer)
B. Cysteine protease
C. Amoebopore
D. Neuraminidase

Explanation: **Explanation:** *Entamoeba histolytica* utilizes a multi-step process to invade the colonic mucosa, with **adherence** being the critical first step. **1. Why Lectin is Correct:** The primary virulence factor responsible for adherence is the **Gal/GalNAc lectin** (Galactose and N-acetyl-D-galactosamine-binding lectin). This surface protein allows the trophozoite to bind specifically to galactose and galactosamine residues on the colonic mucin and epithelial cell surfaces. Without this attachment, the amoeba cannot initiate tissue destruction or phagocytosis. **2. Why Other Options are Incorrect:** * **Cysteine Protease:** These are enzymes secreted by the parasite to **degrade** host extracellular matrix proteins (like collagen and elastin) and immune mediators (IgA, IgG), facilitating tissue invasion after adherence has occurred. * **Amoebopore:** These are small peptides that form **pores** in the host cell membrane, leading to cytolysis (cell death). They act after the lectin-mediated binding. * **Neuraminidase:** This enzyme is more characteristic of viruses (like Influenza) or certain bacteria (like *Vibrio cholerae*); it is not a primary virulence factor for *E. histolytica*. **Clinical Pearls for NEET-PG:** * **Pathognomonic Sign:** Presence of **ingested RBCs** (Erythrophagocytosis) in trophozoites is the definitive feature of *E. histolytica* (distinguishing it from the non-pathogenic *E. dispar*). * **Flask-shaped ulcers:** The characteristic lesion produced in the colon. * **Anchovy sauce pus:** The classic description of aspirated material from an Amoebic Liver Abscess. * **Treatment:** Metronidazole/Tinidazole for invasive disease, followed by a luminal amoebicide (e.g., Diloxanide furoate or Paromomycin) to eradicate cysts.

Question 194: Which of the following is a known reservoir for pigs?

A. Taenia solium (Correct Answer)
B. Taenia saginata
C. Trichinella spiralis
D. Ancyclostoma

Explanation: **Explanation:** The correct answer is **Taenia solium**. In the life cycle of *Taenia solium* (the pork tapeworm), humans serve as the definitive host, while **pigs serve as the intermediate host (reservoir)**. Pigs become infected by ingesting eggs or gravid proglottids from human feces. The larvae then develop into *Cysticercus cellulosae* within the pig's muscle tissue. Humans acquire the infection by consuming undercooked "measly pork" containing these larvae. **Analysis of Incorrect Options:** * **Taenia saginata (Beef Tapeworm):** The intermediate host/reservoir is **cattle**, not pigs. Humans are the only definitive host. * **Trichinella spiralis:** While pigs are a major source of human infection, *Trichinella* is unique because the **same individual animal** acts as both the definitive and intermediate host. It does not follow the classic reservoir-to-human transmission pattern of *T. solium*. * **Ancylostoma (Hookworm):** These are soil-transmitted helminths. Their life cycle involves eggs being passed in human feces and larvae developing in the **soil**; they do not require a pig as a reservoir. **High-Yield NEET-PG Pearls:** * **Infective Stage for Humans:** For intestinal taeniasis, it is the *Cysticercus cellulosae* (larva). For **Cysticercosis** (neurocysticercosis), it is the **ingestion of eggs** (via feco-oral route), where humans act as accidental intermediate hosts. * **Diagnostic Feature:** *T. solium* has a scolex with four suckers and a rostellum with hooks ("armed" scolex), whereas *T. saginata* lacks hooks ("unarmed"). * **Drug of Choice:** Praziquantel for intestinal infection; Albendazole + Steroids for Neurocysticercosis.

Question 195: Calabar swelling is due to which of the following?

A. Hypersensitivity to adult worm of Loa-Loa (Correct Answer)
B. Hypersensitivity to larva of Loa-Loa
C. Hypersensitivity to adult worm of Onchocerca
D. Hypersensitivity to larva of Onchocerca

Explanation: **Explanation:** **Calabar swellings** (also known as fugitive swellings) are the clinical hallmark of **Loiasis**, caused by the African eye worm, *Loa loa*. These are transient, localized subcutaneous edematous areas, typically found on the extremities (wrists or ankles). **1. Why Option A is Correct:** The underlying pathophysiology of Calabar swelling is a **Type I hypersensitivity reaction** (IgE-mediated) to the metabolic products or antigens released by the **migrating adult worm** in the subcutaneous tissues. These swellings are non-pitting, itchy, and can last for several days before disappearing and reappearing at a different site. **2. Why the Other Options are Incorrect:** * **Option B:** While microfilariae (larvae) circulate in the blood (diurnal periodicity), the localized subcutaneous swellings are specifically triggered by the movement and antigens of the adult worms, not the larvae. * **Options C & D:** *Onchocerca volvulus* causes **Onchocerciasis** (River Blindness). Its clinical manifestations include subcutaneous nodules (Onchocercomata), "hanging groin," and "leopard skin." The severe inflammatory response in Onchocerciasis is primarily due to the death of **microfilariae** (larvae), not adult worms, often exacerbated by the release of *Wolbachia* endosymbionts. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Chrysops* (Deer fly or Mango fly). * **Diagnosis:** Detection of microfilariae in peripheral blood (collected between **10 AM – 2 PM** due to diurnal periodicity) or visualization of the adult worm crossing the **subconjunctiva** of the eye. * **Drug of Choice:** Diethylcarbamazine (DEC). Note: Use with caution if microfilarial load is high to avoid encephalopathy. * **Eosinophilia:** Loiasis typically presents with very high peripheral blood eosinophil counts.

Question 196: Which of the following is NOT true of kala azar?

A. Persistent hypergammaglobulinemia
B. Pancytopenia
C. Cancrum oris can occur
D. Complete treatment prevents post-kala-azar dermal leishmaniasis (PKDL) (Correct Answer)

Explanation: **Explanation:** The correct answer is **D**. Post-Kala-azar Dermal Leishmaniasis (PKDL) is a non-ulcerative skin lesion that develops after the apparent clinical cure of Visceral Leishmaniasis (Kala-azar). Crucially, **complete treatment of Kala-azar does not prevent PKDL**; in fact, PKDL is considered a post-treatment sequel, occurring in about 5-10% of cases in India (usually 1-2 years after recovery) and up to 50% of cases in Sudan. The parasite persists in the skin despite being cleared from the viscera. **Analysis of Incorrect Options:** * **A. Persistent hypergammaglobulinemia:** This is a hallmark of Kala-azar. There is a massive, polyclonal increase in IgG due to B-cell overstimulation. This leads to a **reversal of the Albumin-Globulin (A:G) ratio**, which is a classic diagnostic clue. * **B. Pancytopenia:** *Leishmania donovani* multiplies within the reticuloendothelial system, including the bone marrow. This leads to bone marrow suppression and hypersplenism, resulting in anemia, leucopenia (specifically monocytopenia), and thrombocytopenia. * **C. Cancrum oris:** In severe, untreated, or malnourished cases, the profound immunosuppression and neutropenia can lead to secondary bacterial infections, including **Cancrum oris** (water cancer/noma), a destructive gangrenous stomatitis. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Sandfly (*Phlebotomus argentipes*). * **Gold Standard Diagnosis:** Bone marrow or Splenic aspiration (showing Amastigote/LD bodies). * **Drug of Choice:** Liposomal Amphotericin B (single dose 10mg/kg is the current WHO recommendation for India). * **PKDL Significance:** Patients with PKDL act as an important **epidemiological reservoir** for the parasite, as the sandfly can ingest the parasite from the skin lesions.

Question 197: Which of the following statements regarding Giardia is true?

A. The cyst form is infective to humans.
B. It primarily inhabits the duodenum and upper jejunum.
C. The trophozoite form possesses two flagella.
D. Both A and B are true. (Correct Answer)

Explanation: **Explanation:** *Giardia lamblia* (also known as *G. duodenalis* or *G. intestinalis*) is a flagellated protozoan that causes giardiasis. Understanding its life cycle and morphology is crucial for NEET-PG. **Why the correct answer is D (Both A and B are true):** * **Statement A is true:** The **cyst** is the infective stage. It is hardy, acid-resistant, and can survive in the environment (especially water) for months. Infection occurs via the fecal-oral route through contaminated food or water. * **Statement B is true:** Once ingested, excystation occurs in the stomach and duodenum. The resulting trophozoites primarily inhabit the **duodenum and upper jejunum**. They attach to the mucosal surface using a ventral sucking disc, leading to malabsorption (steatorrhea). **Why Option C is incorrect:** * The trophozoite form of *Giardia* possesses **four pairs of flagella (total of 8)**, not two. It is characteristically pear-shaped (pyriform) and contains two nuclei, giving it a "monkey-face" or "owl-eye" appearance under the microscope. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** The cyst is oval with 4 nuclei (quadrinucleate), while the trophozoite is pear-shaped with 2 nuclei. * **Clinical Presentation:** Characterized by foul-smelling, greasy stools (**steatorrhea**) that float, flatulence, and abdominal cramps. It does **not** cause bloody diarrhea (non-invasive). * **Diagnosis:** Stool microscopy (cysts/trophozoites) or the **String Test (Entero-test)** to sample duodenal contents. * **Treatment:** Drug of choice is **Metronidazole** or Tinidazole. * **Association:** Increased incidence is seen in patients with **Selective IgA deficiency**.

Question 198: Which of the following is true regarding Giardia lamblia?

A. Malabsorption is commonly seen.
B. The trophozoite form is binucleate. (Correct Answer)
C. Diarrhea is seen.
D. Jejunal wash fluid is diagnostic.

Explanation: **Explanation:** *Giardia lamblia* (also known as *G. duodenalis* or *G. intestinalis*) is a flagellated protozoan that primarily inhabits the duodenum and upper jejunum. **Why Option B is correct:** The morphology of the *Giardia* trophozoite is a high-yield topic. It is characteristically pear-shaped (pyriform) and possesses **two nuclei** (binucleate) positioned symmetrically, giving it a classic "monkey-face" or "owl-eye" appearance under the microscope. It also features four pairs of flagella and a ventral sucking disc for attachment. **Analysis of other options:** * **Option A & C:** While malabsorption (steatorrhea) and diarrhea are classic clinical features of Giardiasis, these options are technically **incorrect in the context of this specific question** because they are not *always* seen. Many infections are asymptomatic. In a "single best answer" format, morphological facts (like being binucleate) are considered absolute truths compared to variable clinical presentations. * **Option D:** While a jejunal aspirate or biopsy can detect trophozoites, it is **not the first-line diagnostic method**. The gold standard for initial diagnosis is stool microscopy (detecting cysts/trophozoites) or stool antigen detection (ELISA). Invasive procedures like the "Entero-test" (string test) or jejunal washes are reserved for cases where stool exams are repeatedly negative despite high clinical suspicion. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Duodenum and upper jejunum (acidic environment). * **Infective Form:** Mature Cyst (quadrinucleate). * **Pathogenesis:** Causes "falling leaf" motility; leads to blunting of villi but **does not** invade the mucosa (non-invasive). * **Clinical Sign:** Foul-smelling, greasy stools (steatorrhea) that float in water. * **Drug of Choice:** Metronidazole or Tinidazole. * **Association:** Increased prevalence in patients with Common Variable Immunodeficiency (IgA deficiency).

Question 199: What is the required water host for Schistosoma species?

A. Fish
B. Cyclops
C. Snails (Correct Answer)
D. Crabs

Explanation: **Explanation:** **Schistosoma species** (Blood Flukes) are unique trematodes that require a specific **intermediate host** to complete their life cycle. The correct answer is **Snails** because the life cycle involves the release of *miracidia* from eggs (excreted in stool or urine), which must infect specific freshwater snails. Inside the snail, the parasite undergoes asexual reproduction to transform into *cercariae*, the infective stage for humans. * **Schistosoma haematobium:** Uses *Bulinus* snails. * **Schistosoma mansoni:** Uses *Biomphalaria* snails. * **Schistosoma japonicum:** Uses *Oncomelania* snails. **Why other options are incorrect:** * **Fish:** Serve as the second intermediate host for *Clonorchis sinensis* and *Opisthorchis*, but not for Schistosomes. * **Cyclops:** These are the intermediate hosts for *Dracunculus medinensis* (Guinea worm) and *Diphyllobothrium latum* (Fish tapeworm). * **Crabs/Crayfish:** These serve as the second intermediate host for *Paragonimus westermani* (Lung fluke). **High-Yield Clinical Pearls for NEET-PG:** * **Mode of Infection:** Unlike most trematodes (which are ingested), Schistosomes infect humans via **direct skin penetration** by cercariae in contaminated water. * **Morphology:** They are **non-hermaphroditic** (dioecious); the male has a **gynecophoric canal** where the female resides. * **Pathology:** *S. haematobium* is strongly associated with **Squamous Cell Carcinoma of the bladder** and terminal hematuria. * **Diagnostic Stage:** Detection of characteristic eggs with spines (e.g., Terminal spine in *S. haematobium*; Lateral spine in *S. mansoni*).

Question 200: Which of the following is NOT responsible for pulmonary eosinophilia?

A. Ascaris lumbricoides
B. Paragonimus westermanii
C. Wuchereria bancrofti
D. Babesia microti (Correct Answer)

Explanation: **Explanation:** The concept of **Pulmonary Eosinophilia** (often associated with Loeffler’s syndrome or Tropical Pulmonary Eosinophilia) occurs when helminthic parasites migrate through the lungs as part of their life cycle or reside in the pulmonary parenchyma, triggering a Type I hypersensitivity reaction. **Why Babesia microti is the correct answer:** * **Babesia microti** is an intraerythrocytic protozoan (similar to Malaria) transmitted by the *Ixodes* tick. It infects Red Blood Cells (RBCs), leading to hemolytic anemia and fever. It does **not** have a pulmonary migration phase and does not induce a significant eosinophilic response, making it the correct "except" choice. **Analysis of incorrect options:** * **Ascaris lumbricoides:** A classic cause of **Loeffler’s syndrome**. During its life cycle, larvae migrate from the portal circulation into the alveoli, causing cough, dyspnea, and transient pulmonary infiltrates with peripheral eosinophilia. * **Paragonimus westermanii:** Known as the "Lung Fluke." Adult worms reside in the lung parenchyma, forming cystic cavities. This leads to chronic cough, hemoptysis (mimicking TB), and significant local and systemic eosinophilia. * **Wuchereria bancrofti:** Responsible for **Tropical Pulmonary Eosinophilia (TPE)**. This is a distinct clinical entity caused by an exaggerated immune response to microfilariae trapped in the pulmonary microvasculature, characterized by nocturnal cough, wheezing, and massive eosinophilia (>3000/µL). **High-Yield Clinical Pearls for NEET-PG:** * **Loeffler’s Syndrome Mnemonic (NAAAS):** **N**ecator americanus, **A**scaris lumbricoides, **A**ncylostoma duodenale, **A**ncylostoma braziliense, **S**trongyloides stercoralis. * **Tropical Pulmonary Eosinophilia (TPE):** Associated with high IgE levels and a positive Filariasis skin test; it responds dramatically to Diethylcarbamazine (DEC). * **Babesia Identification:** Look for "Maltese Cross" appearance (tetrads) on a Giemsa-stained thick/thin blood smear.

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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