Parasitology Practice Questions

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).

Q: Steatorrhea associated with Giardia infection is seen in which immunoglobulin deficiency?

IgA. **Explanation:** **1. Why IgA is the correct answer:** Secretory IgA (sIgA) is the primary immunoglobulin responsible for mucosal immunity. It acts as the first line of defense in the gastrointestinal tract by preventing the attachment of pathogens to the intestinal epithelium. In patients with **Selective IgA Deficiency** or **Common Variable Immunodeficiency (CVID)**, the lack of mucosal IgA allows *Giardia lamblia* trophozoites to adhere extensively to the duodenal and jejunal mucosa. This leads to villous atrophy and malabsorption, manifesting clinically as chronic diarrhea and **steatorrhea** (fatty stools). **2. Why other options are incorrect:** * **IgE:** Primarily involved in Type I hypersensitivity reactions and defense against helminths (multicellular parasites). It does not play a significant role in preventing protozoal adhesion. * **IgG:** The most abundant systemic antibody, crucial for opsonization and neutralizing toxins in the blood and tissues, but it is not the dominant antibody on mucosal surfaces. * **IgM:** The first antibody produced during a primary immune response. While it can be secreted onto mucosa in small amounts (especially as a compensatory mechanism in IgA deficiency), it is not the primary diagnostic association for Giardia-induced steatorrhea. **3. NEET-PG High-Yield Pearls:** * **Selective IgA Deficiency** is the most common primary immunodeficiency. * **Clinical Association:** Patients are often asymptomatic but have an increased risk of respiratory infections, GI infections (*Giardia*), and **Anaphylaxis during blood transfusions** (due to anti-IgA antibodies). * **Giardia Diagnosis:** Stool microscopy (cysts/trophozoites) is standard, but the **Entero-test (String test)** or duodenal aspiration may be used if stool samples are negative. * **Drug of Choice:** Metronidazole or Tinidazole.

Q: A patient with prolonged diarrhea undergoes esophagogastroduodenoscopy. Biopsy of the small intestine demonstrates numerous crescent-shaped protozoa adjacent to the epithelial brush border. Which of the following organisms is the most likely pathogen?

Giardia lamblia. ### Explanation **Correct Answer: C. Giardia lamblia** The clinical presentation and histopathological findings are classic for **Giardiasis**. * **Mechanism:** *Giardia lamblia* (or *G. duodenalis*) trophozoites are pear-shaped or **crescent-shaped** (when viewed laterally) and possess a ventral sucking disc. They attach to the **brush border of the duodenal and jejunal enterocytes** but do not invade the mucosa. * **Pathology:** This attachment leads to the blunting of villi and malabsorption, resulting in foul-smelling, non-bloody, fatty diarrhea (steatorrhea). The biopsy finding of crescentic organisms "falling off" or "clinging to" the epithelial surface is a high-yield diagnostic feature. **Analysis of Incorrect Options:** * **A. Entamoeba histolytica:** Primarily affects the **colon** (not the small intestine). Histology shows "flask-shaped ulcers" and trophozoites with ingested RBCs (erythrophagocytosis). * **B. Escherichia coli:** This is a bacterium, not a protozoan. While ETEC/EPEC cause diarrhea, they would not appear as large crescent-shaped protozoa on biopsy. * **D. Naegleria fowleri:** This is a free-living amoeba that causes **Primary Amoebic Meningoencephalitis (PAM)**. It enters through the cribriform plate via nasal inhalation and does not cause intestinal disease. **High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** Duodenum and upper jejunum (acidic pH favors excystation). * **Diagnosis:** Stool microscopy (cysts/trophozoites), String test (Entero-test), or biopsy. * **Morphology:** Trophozoite has a "Monkey face" or "Owl's eye" appearance (2 nuclei, 4 pairs of flagella). * **Risk Factors:** IgA deficiency (predisposes to chronic giardiasis). * **Treatment:** Metronidazole or Tinidazole.

Q: Persistent diarrhea in AIDS is caused by which of the following?

Cryptosporidia. **Explanation:** **Cryptosporidium parvum** is the most common cause of chronic, persistent, and life-threatening watery diarrhea in patients with AIDS, particularly when CD4 counts drop below 100 cells/mm³. It is an acid-fast obligate intracellular protozoan that infects the intestinal epithelium, leading to malabsorption and severe dehydration. **Analysis of Options:** * **Cryptosporidium (Correct):** It is the classic "high-yield" pathogen associated with intractable diarrhea in HIV/AIDS. Diagnosis is typically made via **Modified Acid-Fast staining** (showing red oocysts) or Enzyme Immunoassay (EIA). * **Microspora:** While *Enterocytozoon bieneusi* causes diarrhea in AIDS, it is less common than Cryptosporidium. It requires specialized stains like Chromotrope 2R or electron microscopy for detection. * **Isospora belli (Cystoisospora):** This also causes diarrhea in AIDS, but it is less frequent globally than Cryptosporidium. A key differentiator is that *Isospora* responds well to **Trimethoprim-Sulfamethoxazole (TMP-SMX)**, whereas Cryptosporidium is often refractory to treatment until HAART improves the CD4 count. * **Cryptococcus:** *Cryptococcus neoformans* is a fungus primarily associated with **meningitis** and pulmonary infections in AIDS patients, not primary diarrheal disease. **NEET-PG High-Yield Pearls:** 1. **Staining:** Cryptosporidium, Isospora, and Cyclospora are all **Acid-Fast**. Cryptosporidium oocysts are small (4-6 µm), while Isospora oocysts are larger (20-30 µm) and oval. 2. **Treatment:** The drug of choice for Cryptosporidiosis in immunocompetent patients is **Nitazoxanide**, but in AIDS patients, the definitive treatment is **HAART** to restore immunity. 3. **Transmission:** Often associated with contaminated water supplies (oocysts are resistant to chlorination).

Q: A patient presented with subcutaneous nodules over the Iliac Crest and snowflake opacity in the eye. Skin scraping contains microfilaria and adult worms. Which parasite is likely responsible?

Onchocerca volvulus. ### Explanation The correct answer is **Onchocerca volvulus**. This parasite is the causative agent of **Onchocerciasis (River Blindness)**. #### Why Onchocerca volvulus is correct: The clinical presentation is classic for Onchocerciasis. * **Subcutaneous Nodules:** Known as **Onchocercomas**, these contain both adult worms and microfilariae. They typically occur over bony prominences like the iliac crest or skull. * **Ocular Involvement:** Microfilariae migrating to the eye cause **Snowflake Opacities** (punctate keratitis), which are reversible inflammatory lesions. Chronic infection leads to sclerosing keratitis and blindness. * **Diagnosis:** Unlike other filarial worms, *O. volvulus* microfilariae are found in **skin snips/scrapings**, not in the blood. #### Why other options are incorrect: * **Loa loa (African Eye Worm):** Characterized by transient **Calabar swellings** and the visible migration of the adult worm across the subconjunctiva. Microfilariae are found in the **blood** (diurnal periodicity). * **Brugia timori:** Causes lymphatic filariasis (elephantiasis) primarily in the lower limbs. Microfilariae are found in the **blood** and have a nocturnal periodicity. * **Mansonella ozzardi:** Generally asymptomatic or causes mild skin rashes/joint pain. Microfilariae are found in the **blood** and lack a sheath. #### High-Yield Clinical Pearls for NEET-PG: * **Vector:** *Simulium* fly (Blackfly), which breeds in fast-flowing rivers. * **Skin Changes:** "Leopard skin" (patchy depigmentation) and "Lizard skin" (atrophy/thickening). * **Hanging Groin:** Loss of elasticity in the inguinal skin leading to pendulous lymph nodes. * **Drug of Choice:** **Ivermectin** (Note: Diethylcarbamazine is contraindicated as it can trigger a severe Mazzotti reaction). * **Wolbachia:** An endosymbiotic bacteria required for the fertility of the adult worm; targeting it with Doxycycline can sterilize the parasite.

Q: Which one of the following is NOT a neuroparasite?

Trichinella spiralis. **Explanation:** The term **neuroparasite** refers to parasites that have a predilection for the Central Nervous System (CNS) or cause significant clinical disease by invading brain tissue. **Why Trichinella spiralis is the correct answer:** *Trichinella spiralis* is primarily a **tissue nematode** that causes trichinellosis. While the larvae migrate through various organs (including the brain, where they can cause transient encephalitis), they **cannot encyst in the CNS**. They have a specific tropism for **striated skeletal muscle** (e.g., diaphragm, deltoid, extraocular muscles), where they form characteristic calcified cysts. Therefore, it is classified as a muscle parasite rather than a neuroparasite. **Analysis of Incorrect Options:** * **Taenia solium:** The larval stage (*Cysticercus cellulosae*) has a high affinity for the brain, causing **Neurocysticercosis (NCC)**, the most common cause of adult-onset seizures worldwide. * **Naegleria fowleri:** Known as the "brain-eating amoeba," it enters via the olfactory neuroepithelium to cause **Primary Amoebic Meningoencephalitis (PAM)**, which is rapidly fatal. * **Acanthamoeba:** An opportunistic free-living amoeba that causes **Granulomatous Amoebic Encephalitis (GAE)**, particularly in immunocompromised individuals. **High-Yield Clinical Pearls for NEET-PG:** * **Most common CNS parasite:** *Taenia solium* (Neurocysticercosis). * **Drug of choice for NCC:** Albendazole (Praziquantel is an alternative). * **Diagnostic feature of Trichinella:** Muscle biopsy showing "coiled larvae" and elevated serum **creatine kinase (CK)** levels. * **Free-living amoebae:** *Naegleria* (freshwater history), *Acanthamoeba* (contact lens use/keratitis), and *Balamuthia mandrillaris* are all neuroparasites.

Q: The number of pairs of flagella in the depicted organism is:

4. ***4*** - **Giardia lamblia** trophozoites possess **4 pairs of flagella** (8 flagella total), which is a key diagnostic feature for identification. - The **trophozoite** has a characteristic **pear-shaped** morphology with **two nuclei** giving it a "face-like" appearance under microscopy. *1* - **Leishmania** species have only **1 flagellum** in their promastigote form, not pairs of flagella. - This count is too low for **Giardia lamblia**, which requires multiple flagella for its characteristic tumbling motility. *2* - **Trichomonas vaginalis** has **1 pair of flagella** (4 flagella total) plus an **undulating membrane**. - This number is insufficient for **Giardia**, which needs more flagella for its complex swimming pattern. *3* - No major **flagellated parasite** of clinical significance possesses exactly **3 pairs of flagella**. - This count falls short of **Giardia's** requirement for **4 pairs** to maintain its characteristic motility and adherence mechanisms.

Question 1

Ziemann dots are seen in which Plasmodium species?

Accepted Answer

P. Malariae

Answer

P. Vivax

Answer

P. Falciparum

Answer

P. Ovale

Question 2

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 3

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

Question 4

Steatorrhea associated with Giardia infection is seen in which immunoglobulin deficiency?

Accepted Answer

IgA

Answer

IgE

Answer

IgG

Answer

IgM

Question 5

A patient with prolonged diarrhea undergoes esophagogastroduodenoscopy. Biopsy of the small intestine demonstrates numerous crescent-shaped protozoa adjacent to the epithelial brush border. Which of the following organisms is the most likely pathogen?

Accepted Answer

Giardia lamblia

Answer

Entamoeba histolytica

Answer

Escherichia coli

Answer

Naegleria fowleri

Question 6

Which of the following is NOT true of Giardiasis?

Accepted Answer

Complement fixation test is diagnostic

Answer

Stool contains only cysts

Answer

Habitat is the colon

Answer

Trophozoites and cysts are found in the duodenum

Question 7

Persistent diarrhea in AIDS is caused by which of the following?

Accepted Answer

Cryptosporidia

Answer

Microspora

Answer

Cryptococcus

Answer

Isospora belli

Question 8

A patient presented with subcutaneous nodules over the Iliac Crest and snowflake opacity in the eye. Skin scraping contains microfilaria and adult worms. Which parasite is likely responsible?

Accepted Answer

Onchocerca volvulus

Answer

Loa loa

Answer

Brugia timori

Answer

Mansonella ozzardi

Question 9

Which one of the following is NOT a neuroparasite?

Accepted Answer

Trichinella spiralis

Answer

Taenia solium

Answer

Acanthamoeba

Answer

Naegleria

Question 10

The number of pairs of flagella in the depicted organism is:

Accepted Answer

4

Answer

1

Answer

2

Answer

3

Parasitology — MCQs

Parasitology — MCQs

On this page

Practice by Chapter

Want unlimited practice?