Parasitology Practice Questions

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**.

Q: Ziemann dots are seen in which Plasmodium species?

P. Malariae. **Explanation:** The correct answer is **C. P. Malariae**. In parasitology, "stippling" refers to the characteristic morphological changes (dots) seen in the cytoplasm of infected Red Blood Cells (RBCs) on a peripheral smear. These dots are essential for species identification. **1. Why P. Malariae is correct:** * **Ziemann’s dots** are fine, pinkish-to-lavender dust-like granules that appear in the cytoplasm of RBCs infected with *Plasmodium malariae*. These dots are typically harder to visualize than those in other species and often require prolonged staining. **2. Analysis of Incorrect Options:** * **A. P. Vivax:** Characterized by **Schüffner’s dots**. These are fine, round, pinkish-yellow granules. Infected RBCs are also typically enlarged (hypertrophied). * **B. P. Falciparum:** Characterized by **Maurer’s dots** (or Maurer’s clefts). These are coarse, irregular, dark-red spots seen in the cytoplasm of infected RBCs. * **D. P. Ovale:** Also shows **Schüffner’s dots** (sometimes specifically called James's dots). The RBCs are often oval-shaped with fimbriated (tufted) edges. **3. NEET-PG High-Yield Pearls:** * **RBC Age Preference:** *P. vivax/ovale* prefer young RBCs (reticulocytes); *P. malariae* prefers old RBCs; *P. falciparum* is "indiscriminate" (infects all ages), leading to high parasitemia. * **Morphology of P. Malariae:** Look for **"Band forms"** (trophozoites) and **"Daisy head/Rosette"** appearance (schizonts). * **Clinical Feature:** *P. malariae* causes **Quartan malaria** (fever every 72 hours) and is associated with **Nephrotic Syndrome** (Quartan Malarial Nephropathy).

Q: Man serves as both the intermediate and definitive host for which of the following parasites?

Taenia solium. **Explanation:** In parasitology, the **definitive host** is where the parasite reaches sexual maturity (adult stage), while the **intermediate host** is where the larval or asexual stages develop. **Taenia solium (Pork Tapeworm)** is unique because humans can play both roles: 1. **Definitive Host:** Occurs when humans ingest undercooked pork containing **cysticerci**. The larvae develop into adult tapeworms in the small intestine (**Intestinal Taeniasis**). 2. **Intermediate Host:** Occurs when humans ingest **eggs** (via feco-oral route or autoinfection). The eggs hatch into oncospheres that penetrate the intestinal wall and migrate to tissues (brain, muscles) to form cysticerci, leading to **Cysticercosis**. **Analysis of Incorrect Options:** * **B. Taenia saginata (Beef Tapeworm):** Humans are **only** definitive hosts. Cattle serve as the intermediate host. Ingesting eggs does not cause cysticercosis in humans. * **C. Diphyllobothrium latum (Fish Tapeworm):** Humans are definitive hosts. It requires two intermediate hosts: Cyclops (1st) and freshwater fish (2nd). * **D. Dicrocoelium dendriticum (Lancet Liver Fluke):** Humans are accidental definitive hosts. Intermediate hosts are snails and ants. **High-Yield NEET-PG Pearls:** * **Other parasites** where man acts as both hosts: *Hymenolepis nana*, *Strongyloides stercoralis*, and *Trichinella spiralis*. * **Neurocysticercosis (NCC):** The most common cause of adult-onset seizures in India; caused by *T. solium* eggs, **not** by eating pork. * **Diagnosis:** Stool microscopy for eggs/proglottids (Taeniasis) and MRI/CT "starry sky appearance" (Cysticercosis).

Question 1

Autoinfection is NOT seen in which of the following?

Accepted Answer

Hymenolepis diminuta

Answer

Hymenolepis nana

Answer

Strongyloidosis

Answer

Taenia solium

Question 2

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

Accepted Answer

Lectin

Answer

Cysteine protease

Answer

Amoebopore

Answer

Neuraminidase

Question 3

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 4

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 5

Which of the following is NOT responsible for pulmonary eosinophilia?

Accepted Answer

Babesia microti

Answer

Ascaris lumbricoides

Answer

Paragonimus westermanii

Answer

Wuchereria bancrofti

Question 6

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 7

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

Question 8

Ziemann dots are seen in which Plasmodium species?

Accepted Answer

P. Malariae

Answer

P. Vivax

Answer

P. Falciparum

Answer

P. Ovale

Question 9

What is the diagnostic test of choice for extra-intestinal invasive amoebiasis?

Accepted Answer

ELISA

Answer

Counter immuno-electrophoresis

Answer

Complement fixation test

Answer

Indirect haemagglutination test

Question 10

Man serves as both the intermediate and definitive host for which of the following parasites?

Accepted Answer

Taenia solium

Answer

Taenia saginata

Answer

Diphyllobothrium latum

Answer

Dicrocoelium dendriticum

Parasitology — MCQs

Parasitology — MCQs

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