Parasitology Practice Questions

Q: Which of the following statements is TRUE regarding visceral leishmaniasis?

Antimonials are useful drugs for its treatment.. **Explanation:** **Visceral Leishmaniasis (Kala-azar)** is a systemic protozoal infection caused by the *Leishmania donovani* complex, transmitted by the bite of the female sandfly (*Phlebotomus argentipes*). 1. **Why Option C is Correct:** **Pentavalent Antimonials** (e.g., Sodium Stibogluconate and Meglumine Antimoniate) have historically been the mainstay of treatment. While resistance is increasing (especially in Bihar, India), they remain a classic pharmacological association for the disease. Currently, **Liposomal Amphotericin B** is the drug of choice due to higher efficacy and lower toxicity. 2. **Why Other Options are Incorrect:** * **Option A:** *L. tropica* and *L. major* cause **Cutaneous Leishmaniasis** (Oriental Sore). Visceral Leishmaniasis is caused by *L. donovani* and *L. infantum*. * **Option B:** The correct term is **Post-Kala-azar Dermal Leishmaniasis (PKDL)**, not "dermatitis." PKDL is a non-ulcerative skin condition that develops months to years after the apparent cure of visceral leishmaniasis, acting as a reservoir for the parasite. * **Option D:** Diagnosis is primarily through **bone marrow or splenic aspiration** (demonstrating Amastigote/LD bodies). Blood smears are rarely sensitive enough; however, the rK39 immunochromatographic test is the preferred rapid diagnostic tool. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad:** Fever, massive splenomegaly, and significant weight loss (cachexia). * **Hematology:** Characterized by **Pancytopenia** and **Hypergammaglobulinemia** (reversed Albumin:Globulin ratio). * **Napier’s Aldehyde Test:** A non-specific screening test based on elevated serum globulins. * **Culture:** NNN (Novy-MacNeal-Nicolle) medium is used to grow the Promastigote stage.

Q: Acute toxoplasmosis is commonly associated with all of the following except?

Myocarditis. **Explanation:** **Toxoplasmosis**, caused by the protozoan *Toxoplasma gondii*, presents differently depending on the host's immune status. In **immunocompetent individuals**, acute infection is asymptomatic in 80–90% of cases. When symptoms do occur, the most common clinical manifestation is **painless lymphadenopathy**. 1. **Why Myocarditis is the Correct Answer:** While *Toxoplasma* can theoretically affect any organ, **myocarditis** is an extremely rare complication in acute, immunocompetent cases. It is typically seen only in **severely immunocompromised patients** (e.g., advanced HIV/AIDS) or as part of a disseminated infection in neonates. Therefore, it is not "commonly associated" with standard acute toxoplasmosis. 2. **Analysis of Incorrect Options:** * **Cervical and Axillary Lymphadenopathy (Options A & B):** These are the hallmark signs of acute toxoplasmosis. The cervical nodes are most frequently involved, followed by axillary and inguinal nodes. The nodes are usually discrete and non-suppurative. * **Muscle Pain (Option C):** A "mononucleosis-like syndrome" is common in acute toxoplasmosis, characterized by fever, headache, fatigue, and **myalgia** (muscle pain) due to the systemic spread of tachyzoites. **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Cat (sexual cycle occurs in the intestinal epithelium). * **Intermediate Host:** Humans and other mammals (asexual cycle). * **Infective Forms:** Oocysts (from cat feces), Tissue cysts (undercooked meat), and Tachyzoites (transplacental). * **Diagnosis:** Serology (Sabin-Feldman Dye Test is the gold standard; IgM indicates acute infection). * **Congenital Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Treatment of Choice:** Pyrimethamine + Sulfadiazine (with Folinic acid).

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

Lectin. **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.

Q: Calabar swelling is due to which of the following?

Hypersensitivity to adult worm of Loa-Loa. **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.

Q: An AIDS patient is presenting with watery diarrhea. What could be the causative organism?

Cryptosporidia. **Explanation:** In an immunocompromised patient, particularly those with AIDS (CD4 count <200 cells/mm³), the most common cause of chronic, severe, watery diarrhea is **Cryptosporidium parvum**. **1. Why Cryptosporidia is correct:** Cryptosporidium is an acid-fast protozoan that infects the intestinal epithelium. While it causes self-limiting diarrhea in healthy individuals, it leads to life-threatening, voluminous, non-bloody watery diarrhea in AIDS patients due to the lack of T-cell mediated immunity. Diagnosis is typically made using **Modified Acid-Fast staining** (Kinyoun stain), which reveals bright red oocysts. **2. Why other options are incorrect:** * **Candida:** While common in AIDS (oral thrush, esophagitis), it rarely causes primary watery diarrhea. It is more associated with mucosal infections. * **Vibrio cholerae:** Causes "rice-water" stools through a toxin-mediated mechanism, but it is an acute epidemic infection and not specifically associated with the chronic immunosuppression of AIDS. * **ETEC:** A common cause of Traveler’s diarrhea. Like Cholera, it causes acute watery diarrhea but is not a characteristic opportunistic infection defining the clinical course of an AIDS patient. **Clinical Pearls for NEET-PG:** * **Other AIDS-related Diarrhea:** If CD4 <50, consider **Microsporidia** (very small spores) or **MAC (Mycobacterium avium complex)**. * **Staining:** Cryptosporidium, Isospora, and Cyclospora are all **Acid-Fast**. Cryptosporidium is the smallest (4-6 µm). * **Treatment:** In AIDS patients, the primary treatment is **HAART** (to boost CD4 count); Nitazoxanide has limited efficacy in severe immunosuppression.

Q: What is the primary method for diagnosing toxoplasmosis in newborns?

Detecting IgM antibodies to Toxoplasma. **Explanation:** The diagnosis of congenital infections, including Toxoplasmosis, relies on distinguishing between maternal antibodies and those produced by the fetus. **Why Option B is Correct:** IgM antibodies do not cross the placenta due to their large molecular size (pentameric structure). Therefore, the presence of **Toxoplasma-specific IgM** in a newborn’s serum is definitive evidence of an active, congenital infection, as these antibodies must have been produced by the infant's own immune system in response to the parasite. **Analysis of Incorrect Options:** * **Option A (IgG):** Maternal IgG antibodies cross the placenta freely via neonatal Fc receptors to provide passive immunity. Detecting IgG in a newborn often reflects maternal transfer rather than fetal infection. These antibodies can persist for up to 12 months, making them unreliable for immediate neonatal diagnosis. * **Options C & D (IgA & IgE):** While IgA and IgE can be produced by the fetus and are sometimes used as adjunctive tests (IgA is often more sensitive than IgM), **IgM remains the primary and standard screening method** in clinical practice and for examination purposes. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad of Congenital Toxoplasmosis:** Chorioretinitis (most common), Hydrocephalus, and Intracranial calcifications (diffuse/scattered). * **Gold Standard for Prenatal Diagnosis:** PCR of amniotic fluid. * **Treatment:** Pyrimethamine, Sulfadiazine, and Folinic acid (Leucovorin) for one year. * **Key Distinction:** Unlike CMV (periventricular calcifications), Toxoplasmosis causes **diffuse parenchymal calcifications**.

Q: An anxious mother brought her 4-year-old daughter to the pediatrician. The girl was passing loose, bulky stools for the past 20 days, often associated with abdominal pain. Stool examination showed pear-shaped, flagellated trophozoites and cysts with four nuclei. What is the likely causative organism?

Giardia lamblia. ### Explanation The clinical presentation and morphology described are classic for **Giardiasis**, caused by **_Giardia lamblia_** (also known as *G. duodenalis* or *G. intestinalis*). **Why Option B is Correct:** * **Clinical Presentation:** The patient has chronic diarrhea (20 days) characterized as "bulky" and "loose." This suggests **malabsorption** and steatorrhea, which occurs because *Giardia* trophozoites coat the duodenal mucosa, leading to the blunting of villi. * **Morphology:** The description of **pear-shaped, flagellated trophozoites** (often described as having a "falling leaf" motility and a "monkey face" appearance) and **cysts with four nuclei** is pathognomonic for *Giardia*. **Why Other Options are Incorrect:** * **A. *Entamoeba histolytica*:** Causes amoebic dysentery (bloody stools). Trophozoites are not flagellated and typically show ingested RBCs; cysts have 1–4 nuclei but a different internal structure (chromatoid bodies). * **C. *Cryptosporidium*:** Typically causes profuse watery diarrhea. It is diagnosed via modified acid-fast staining showing red-stained oocysts; it does not have a flagellated trophozoite stage. * **D. *E. coli*:** While certain strains (like EPEC) cause childhood diarrhea, they are bacteria, not protozoa, and would not present with flagellated trophozoites or quadrinucleated cysts in a stool ova and parasite exam. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Primarily the **duodenum** and upper jejunum (acidic pH). * **Diagnosis:** Stool microscopy is standard, but **Entero-test (String test)** can be used if stool is negative. * **Antigen Detection:** Immunochromatographic tests for Giardia-specific antigen 65 (GSA 65) are highly sensitive. * **Treatment:** Drug of choice is **Tinidazole** (single dose) or Metronidazole. * **Association:** Increased incidence in patients with **Selective IgA deficiency**.

Question 1

Which of the following is true about amoebic colitis?

Accepted Answer

Caused by Entamoeba histolytica

Answer

The cyst contains eight nuclei

Answer

Flask-shaped ulcers are present

Answer

The cecum is most commonly affected

Question 2

Which of the following statements is TRUE regarding visceral leishmaniasis?

Accepted Answer

Antimonials are useful drugs for its treatment.

Answer

It is caused by L. tropica.

Answer

Post-leishmaniasis dermatitis is common.

Answer

It is diagnosed by blood smear.

Question 3

Acute toxoplasmosis is commonly associated with all of the following except?

Accepted Answer

Myocarditis

Answer

Cervical lymphadenopathy

Answer

Axillary lymphadenopathy

Answer

Muscle pain

Question 4

Autoinfection is NOT seen in which of the following?

Accepted Answer

Hymenolepis diminuta

Answer

Hymenolepis nana

Answer

Strongyloidosis

Answer

Taenia solium

Question 5

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

Accepted Answer

Lectin

Answer

Cysteine protease

Answer

Amoebopore

Answer

Neuraminidase

Question 6

Calabar swelling is due to which of the following?

Accepted Answer

Hypersensitivity to adult worm of Loa-Loa

Answer

Hypersensitivity to larva of Loa-Loa

Answer

Hypersensitivity to adult worm of Onchocerca

Answer

Hypersensitivity to larva of Onchocerca

Question 7

An AIDS patient is presenting with watery diarrhea. What could be the causative organism?

Accepted Answer

Cryptosporidia

Answer

Candida

Answer

Vibrio cholerae

Answer

ETEC (Enterotoxigenic Escherichia coli)

Question 8

Which of the following is NOT responsible for pulmonary eosinophilia?

Accepted Answer

Babesia microti

Answer

Ascaris lumbricoides

Answer

Paragonimus westermanii

Answer

Wuchereria bancrofti

Question 9

What is the primary method for diagnosing toxoplasmosis in newborns?

Accepted Answer

Detecting IgM antibodies to Toxoplasma

Answer

Detecting IgG antibodies against Toxoplasma

Answer

Detecting IgA antibodies to Toxoplasma

Answer

Detecting IgE antibodies to Toxoplasma

Question 10

An anxious mother brought her 4-year-old daughter to the pediatrician. The girl was passing loose, bulky stools for the past 20 days, often associated with abdominal pain. Stool examination showed pear-shaped, flagellated trophozoites and cysts with four nuclei. What is the likely causative organism?

Accepted Answer

Giardia lamblia

Answer

Entamoeba histolytica

Answer

Cryptosporidium

Answer

E. coli

Parasitology — MCQs

Parasitology — MCQs

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