Parasitology Practice Questions

Q: A terminally ill HIV infected patient develops focal neurologic signs, dementia, and coma. Amoebic parasites are demonstrated in CSF. Which of the following organisms is most likely to be the causative agent?

Acanthamoeba sp. **Explanation:** The clinical presentation of focal neurological signs, dementia, and coma in an immunocompromised (HIV-infected) patient, combined with the presence of amoebae in the CSF, points toward **Granulomatous Amoebic Encephalitis (GAE)** caused by **Acanthamoeba species**. **1. Why Acanthamoeba is correct:** Acanthamoeba is an opportunistic free-living amoeba. In immunocompromised individuals, it causes GAE, a subacute to chronic infection characterized by a slow onset (weeks to months) involving dementia, personality changes, and focal deficits. It typically spreads hematogenously from a primary site in the skin or lungs to the CNS. **2. Why other options are incorrect:** * **Naegleria fowleri:** Causes **Primary Amoebic Meningoencephalitis (PAM)**. Unlike GAE, PAM is an acute, rapidly fatal infection (death within 5–10 days) that occurs in previously healthy individuals (not necessarily immunocompromised) following exposure to contaminated warm freshwater. * **Entamoeba histolytica:** While it can cause brain abscesses, it is primarily an intestinal pathogen. Brain involvement is rare, secondary to liver abscesses, and presents as an acute abscess rather than the granulomatous encephalitis described. * **Giardia lamblia:** This is a flagellated protozoan that causes intestinal malabsorption and diarrhea; it does not invade the CNS. **Clinical Pearls for NEET-PG:** * **Acanthamoeba:** Also causes **Amoebic Keratitis** (associated with contact lens use) and skin ulcers. Diagnosis is made by finding **both cysts and trophozoites** in tissue/CSF. * **Naegleria fowleri:** Enters via the **cribriform plate**. Diagnosis shows **only trophozoites** in CSF. * **Drug of Choice for GAE:** No standard regimen, but often includes Miltefosine, Fluconazole, or Pentamidine.

Q: Significant titres of indirect hemagglutination (IHA) are seen in all types of amoebiasis except:

Cyst passers. **Explanation:** The Indirect Hemagglutination (IHA) test is a serological assay used to detect circulating antibodies against *Entamoeba histolytica*. The fundamental principle governing its positivity is **tissue invasion**. **Why "Cyst Passers" is the correct answer:** Cyst passers (asymptomatic carriers) harbor the parasite only within the intestinal lumen. Since there is no invasion of the intestinal wall or deeper tissues, the parasite does not come into contact with the host’s immune system to trigger a systemic humoral response. Consequently, antibody titers remain insignificant or undetectable in these individuals. **Analysis of Incorrect Options:** * **Acute Amoebic Dysentery:** This involves mucosal invasion and ulceration of the colon. The breach of the intestinal barrier allows for antibody production, leading to significant IHA titers in approximately 60-70% of cases. * **Liver Abscess:** This is the most common form of extra-intestinal amoebiasis. Because it involves deep tissue invasion and a robust systemic immune response, IHA titers are highly sensitive (positive in >95% of cases) and usually reach very high levels. * **Brain Abscess:** Similar to liver abscesses, this represents a severe extra-intestinal spread where tissue destruction is significant, leading to high antibody titers. **High-Yield Clinical Pearls for NEET-PG:** * **Serology vs. Microscopy:** Serology (IHA, ELISA) is the gold standard for diagnosing **extra-intestinal** amoebiasis, whereas stool microscopy is preferred for **intestinal** amoebiasis. * **Persistence:** IHA titers can remain positive for several years even after successful treatment; thus, a single positive test may not always indicate an active infection in endemic areas. * **E. dispar vs. E. histolytica:** Serology helps differentiate these two; *E. dispar* (non-pathogenic) does not cause a rise in antibody titers.

Q: Which of the following produces bile-stained eggs?

Ascaris. **Explanation:** The correct answer is **Ascaris lumbricoides**. In parasitology, eggs are classified as "bile-stained" if they absorb the golden-brown pigment of bile while passing through the human intestine. **1. Why Ascaris is correct:** *Ascaris lumbricoides* (Roundworm) eggs are characterized by a thick, translucent shell surrounded by a coarse, wavy, or mammillated albuminous coat. This outer layer is highly permeable to bile pigments, giving the eggs their characteristic **golden-brown color**. Both fertilized and unfertilized eggs of Ascaris are bile-stained. **2. Why the other options are incorrect:** * **Ancylostoma duodenale & Necator americanus (Hookworms):** These parasites produce eggs that are colorless (non-bile stained), oval, and surrounded by a thin, transparent hyaline membrane. They are typically seen in the 4-to-8-cell cleavage stage. * **Enterobius vermicularis (Pinworm):** These eggs are also non-bile stained. They have a characteristic plano-convex shape (one side flat, one side convex) and are surrounded by a thin, double-layered transparent shell. **3. NEET-PG High-Yield Pearls:** * **Bile-stained eggs (Mnemonic: "TAFT"):** **T**richuris trichiura, **A**scaris lumbricoides, **F**asciola hepatica, **T**aenia species. * **Non-bile stained eggs:** Hookworms (*Ancylostoma, Necator*), *Enterobius vermicularis*, and *Hymenolepis nana*. * **Ascaris Clinical Note:** It is the most common helminthic infection worldwide. Heavy infestations can lead to **Loeffler’s syndrome** (eosinophilic pneumonia) during the larval migratory phase.

Q: Infestation with Clonorchis sinensis increases the risk of which of the following conditions?

Cholangiocarcinoma. **Explanation:** **Clonorchis sinensis** (the Chinese liver fluke) is a parasitic trematode acquired by consuming undercooked freshwater fish. It primarily inhabits the **intrahepatic bile ducts**. **1. Why Cholangiocarcinoma is correct:** Chronic infestation leads to mechanical irritation, localized obstruction, and the release of metabolic products that trigger chronic inflammation and adenomatous hyperplasia of the biliary epithelium. This persistent inflammatory state induces DNA damage and cellular proliferation, making *Clonorchis sinensis* (and *Opisthorchis viverrini*) a Group 1 carcinogen specifically for **Cholangiocarcinoma** (bile duct cancer). **2. Why other options are incorrect:** * **Gall bladder cancer:** While associated with gallstones (cholelithiasis) and "porcelain gallbladder," it is not classically linked to liver flukes, which prefer the bile ducts over the gallbladder. * **Hepatocellular carcinoma (HCC):** HCC is primarily associated with Hepatitis B and C, cirrhosis, and Aflatoxin B1. It arises from hepatocytes, not the biliary epithelium. * **Carcinoma of the head of the pancreas:** This is associated with smoking, chronic pancreatitis, and certain genetic syndromes (e.g., BRCA2, Peutz-Jeghers), but not parasitic fluke infections. **High-Yield Clinical Pearls for NEET-PG:** * **Key Parasites & Cancers:** * *Clonorchis sinensis/Opisthorchis:* Cholangiocarcinoma. * *Schistosoma haematobium:* Squamous cell carcinoma of the Urinary Bladder. * **Diagnostic Clue:** Look for a history of raw fish consumption and imaging showing "dilated intrahepatic bile ducts" with a normal common bile duct. * **Treatment:** **Praziquantel** is the drug of choice for liver fluke infestations.

Q: Duffy blood group antigen negativity confers protection against infection by which Plasmodium species?

Plasmodium vivax. ### Explanation **Correct Answer: C. Plasmodium vivax** **Mechanism of Protection:** *Plasmodium vivax* requires the **Duffy Antigen Receptor for Chemokines (DARC)**, located on the surface of red blood cells (RBCs), to act as a receptor for its **Duffy Binding Protein (DBP)**. This interaction is essential for the merozoite to invade the erythrocyte. Individuals who are **Duffy-negative** (genotype *Fy/Fy*) lack these receptors on their RBCs, making the cells resistant to invasion by *P. vivax*. This phenotype is highly prevalent in West African populations, explaining why *P. vivax* malaria is rare in that region. **Analysis of Incorrect Options:** * **A. Plasmodium falciparum:** Uses multiple alternative receptors (e.g., Glycophorins A, B, and C) for invasion. Protection against *P. falciparum* is instead associated with Sickle Cell Trait (HbAS), G6PD deficiency, and Thalassemia [1]. * **B. Plasmodium ovale:** Primarily uses different, less-defined pathways for entry and is common in West Africa, often "replacing" the niche left by *P. vivax* in Duffy-negative populations. * **D. Plasmodium malariae:** Does not utilize the Duffy antigen for RBC entry; its specific receptor mechanisms are distinct from those of *P. vivax* [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Duffy Status:** Duffy-negative individuals can still be infected by *P. vivax* in rare cases (recent reports from Ethiopia/Madagascar), but for exam purposes, it remains the classic protective factor. * **Reticulocyte Preference:** *P. vivax* and *P. ovale* selectively infect young RBCs (reticulocytes), whereas *P. falciparum* infects RBCs of all ages (leading to high parasitemia) [1]. * **Schüffner’s Dots:** Characteristically seen in RBCs infected with *P. vivax* and *P. ovale*. * **Hypnozoites:** Only *P. vivax* and *P. ovale* form dormant liver stages (hypnozoites), requiring **Primaquine** or **Tafenoquine** for a radical cure [1].

Q: What is the method for diagnosing Hydatid disease?

Serum examination. **Explanation:** Hydatid disease, caused by the larval stage of *Echinococcus granulosus*, is primarily diagnosed through a combination of imaging and serology. **1. Why Serum Examination is the Correct Answer:** Serology (Serum examination) is the mainstay of diagnosis. It detects specific antibodies (IgG) against hydatid antigens. The most commonly used tests include **ELISA** and **Indirect Hemagglutination (IHA)**. For confirmation, the **Immunoblot (Western Blot)** for the 'Arc 5' antigen is highly specific. Serology is preferred because it is non-invasive and carries no risk of anaphylaxis. **2. Why Other Options are Incorrect:** * **Biopsy (A):** This is strictly **contraindicated**. Aspiration or biopsy of a hydatid cyst can lead to the leakage of hydatid fluid, which contains highly antigenic protoscolices. This can trigger life-threatening **anaphylactic shock** or lead to secondary peritoneal hydatidosis (seeding). * **X-ray (B):** While X-rays may show a "water lily sign" or calcification of the cyst wall, they are non-specific and less sensitive than Ultrasound or CT scans. * **Casoni Test (C):** This is an immediate hypersensitivity skin test. While historically important, it is now **obsolete** due to low sensitivity, low specificity, and the risk of inducing sensitivity in the patient. **Clinical Pearls for NEET-PG:** * **Gold Standard Imaging:** Ultrasound is the first-line investigation (look for "Gharbi classification"). * **Treatment of Choice:** Surgical excision (PAIR technique: Puncture, Aspiration, Injection, Re-aspiration) combined with **Albendazole**. * **Microscopy:** Look for "Hydatid sand" (protoscolices, hooklets, and calcareous corpuscles) in the fluid. * **Eosinophilia:** Present in only about 20-25% of cases; its absence does not rule out the disease.

Q: Cysticercosis is caused by which of the following parasites?

Taenia solium. **Explanation:** **Cysticercosis** is a systemic parasitic infection caused by the larval stage (*Cysticercus cellulosae*) of the pork tapeworm, **Taenia solium**. 1. **Why Taenia solium is correct:** In the normal life cycle, humans are definitive hosts (harboring the adult worm) by eating undercooked pork containing cysticerci. However, if a human accidentally ingests **T. solium eggs** (via contaminated food/water or autoinfection), the human acts as an **accidental intermediate host**. The eggs hatch in the intestine, and oncospheres penetrate the gut wall to migrate to muscles, eyes, and the brain, forming cysticerci. **Neurocysticercosis** is the most common cause of acquired epilepsy worldwide. 2. **Why other options are incorrect:** * **Taenia saginata (Beef tapeworm):** Humans are only definitive hosts. Ingesting *T. saginata* eggs does **not** cause cysticercosis in humans because the eggs do not hatch in the human gut. * **Ancylostoma duodenale (Hookworm):** This is a nematode that causes iron-deficiency anemia; it does not form cysts in tissues. * **Echinococcus granulosus (Dog tapeworm):** This causes **Hydatid disease**, characterized by slow-growing unilocular cysts, typically in the liver or lungs. **High-Yield Clinical Pearls for NEET-PG:** * **Mode of Infection:** Cysticercosis is caused by ingesting **eggs**; Taeniasis (intestinal) is caused by ingesting **larvae** (cysticerci). * **Diagnosis:** MRI/CT shows "starry sky appearance" (multiple calcified cysts) or a cyst with a **scolex (dot sign)**. * **Treatment:** Albendazole is the drug of choice; steroids are added to manage inflammation from dying larvae.

Q: A pregnant woman in her first trimester is diagnosed with an infection. Her baby is born with hydrocephalus. Which pathogen is the most likely cause of this infection?

Toxoplasma gondii. **Explanation:** The correct answer is **Toxoplasma gondii**. This protozoan infection is a classic member of the TORCH group. When a mother acquires a primary infection during pregnancy, the parasite can cross the placenta. The classic **Sabine’s Triad** of Congenital Toxoplasmosis includes: 1. **Hydrocephalus** (due to aqueductal stenosis) 2. **Intracranial calcifications** (typically diffuse/scattered) 3. **Chorioretinitis** **Why the other options are incorrect:** * **Herpes Simplex Virus (HSV):** Neonatal HSV is usually acquired during delivery (birth canal). It typically presents with skin-eye-mouth (SEM) vesicles, encephalitis, or disseminated multi-organ failure, rather than congenital hydrocephalus. * **Treponema pallidum (Syphilis):** Congenital syphilis is characterized by "Hutchinson’s Triad" (interstitial keratitis, sensorineural hearing loss, and notched incisors), along with hepatosplenomegaly, snuffles, and skeletal abnormalities (e.g., Sabre shin). * **Cytomegalovirus (CMV):** While CMV is the most common congenital infection and can cause ventriculomegaly, its hallmark finding is **periventricular calcifications** and microcephaly, rather than macrocephaly/hydrocephalus. **High-Yield Pearls for NEET-PG:** * **Toxoplasmosis:** Look for "Diffuse calcifications" and "Hydrocephalus." Treatment for the mother is **Spiramycin**; for the fetus/neonate, it is **Pyrimethamine and Sulfadiazine**. * **CMV:** Look for "Periventricular calcifications" and "Sensorineural hearing loss" (the most common sequela). * **Rule of Thumb:** If the head is large (hydrocephalus), think Toxoplasma. If the head is small (microcephaly), think CMV or Zika.

Question 1

A terminally ill HIV infected patient develops focal neurologic signs, dementia, and coma. Amoebic parasites are demonstrated in CSF. Which of the following organisms is most likely to be the causative agent?

Accepted Answer

Acanthamoeba sp

Answer

Entamoeba histolytica

Answer

Giardia lamblia

Answer

Naegleria fowleri

Question 2

Significant titres of indirect hemagglutination (IHA) are seen in all types of amoebiasis except:

Accepted Answer

Cyst passers

Answer

Acute amoebic dysentery

Answer

Brain abscess

Answer

Liver abscess

Question 3

Which of the following produces bile-stained eggs?

Accepted Answer

Ascaris

Answer

Ancylostoma duodenale

Answer

Enterobius vermicularis

Answer

Necator americanus

Question 4

Infestation with Clonorchis sinensis increases the risk of which of the following conditions?

Accepted Answer

Cholangiocarcinoma

Answer

Gall bladder cancer

Answer

Hepatocellular carcinoma

Answer

Carcinoma of the head of the pancreas

Question 5

Duffy blood group antigen negativity confers protection against infection by which Plasmodium species?

Accepted Answer

Plasmodium vivax

Answer

Plasmodium falciparum

Answer

Plasmodium ovale

Answer

Plasmodium malariae

Question 6

Which of the following is NOT true about toxoplasmosis?

Accepted Answer

IgG antibodies are diagnostic in congenital toxoplasmosis.

Answer

In adults, toxoplasmosis is usually asymptomatic.

Answer

It is an antroponotic disease.

Answer

Encephalitis is uncommon (rare) in immunocompetent individuals.

Question 7

Which statement is true regarding malaria?

Accepted Answer

Red blood cell size is increased in Plasmodium vivax infections

Answer

Rods forms are seen in Plasmodium malariae

Answer

Relapse is seen in Plasmodium falciparum infections

Answer

Both male and female Anopheles mosquitoes transmit the disease

Question 8

What is the method for diagnosing Hydatid disease?

Accepted Answer

Serum examination

Answer

Biopsy

Answer

X-ray

Answer

Casoni test

Question 9

Cysticercosis is caused by which of the following parasites?

Accepted Answer

Taenia solium

Answer

Taenia saginata

Answer

Ancylostoma duodenale

Answer

Echinococcus granulosus

Question 10

A pregnant woman in her first trimester is diagnosed with an infection. Her baby is born with hydrocephalus. Which pathogen is the most likely cause of this infection?

Accepted Answer

Toxoplasma gondii

Answer

Herpes Simplex Virus (HSV)

Answer

Treponema pallidum

Answer

Cytomegalovirus (CMV)

Parasitology — MCQs

Parasitology — MCQs

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