Parasitology Practice Questions

Q: In which host does the flagellar stage of the Leishmania parasite occur?

Sandfly. ### Explanation The life cycle of *Leishmania* involves two distinct morphological stages: the **Amastigote** and the **Promastigote**. **Why the Sandfly is correct:** The **flagellar stage**, known as the **Promastigote**, occurs exclusively within the female **Sandfly** (*Phlebotomus* species). When the sandfly ingests a blood meal containing amastigotes, the parasites transform into elongated, motile promastigotes (15–25 µm) in the midgut. These possess a single anterior flagellum used for attachment and migration to the proboscis, from where they are transmitted to a new host. **Why the other options are incorrect:** * **A, B, and C (Man, Dog, Hamster):** These are all **vertebrate hosts** (Man is the definitive host; dogs and hamsters often serve as reservoirs). In vertebrate hosts, the parasite exists only in the **Amastigote** (LD body) stage. This stage is oval, non-motile, and **aflagellar** (lacks a visible external flagellum). It lives obligately within the phagolysosomes of macrophages. --- ### NEET-PG High-Yield Pearls: * **Infective Form:** Promastigote (injected by sandfly). * **Diagnostic Form:** Amastigote (seen in bone marrow or splenic aspirates, often described as having a nucleus and a rod-shaped kinetoplast). * **Culture Media:** *Leishmania* grows as promastigotes in **NNN (Novy-MacNeal-Nicolle) medium**. * **Vector:** *Phlebotomus argentipes* is the primary vector for Kala-azar in India. * **Gold Standard Diagnosis:** Splenic aspiration (highest sensitivity) but Bone Marrow aspiration is safer and more commonly performed.

Q: Which parasite causes biliary tract obstruction?

Ascaris. **Explanation:** **Ascaris lumbricoides** is the correct answer because it is the most common helminth to cause hepatobiliary complications. Due to its large size (20–35 cm) and high degree of mobility, the adult worm can migrate from the duodenum through the **Ampulla of Vater** into the common bile duct. This leads to mechanical obstruction, resulting in biliary colic, obstructive jaundice, ascending cholangitis, or even acute pancreatitis. In some cases, the worm may die within the duct, acting as a nidus for the formation of pigment gallstones. **Why other options are incorrect:** * **Trichinella spiralis:** This parasite primarily affects skeletal muscle. After ingestion of undercooked meat, the larvae encyst in muscles (like the diaphragm or deltoid), causing myalgia and periorbital edema, but they do not inhabit or obstruct the biliary tract. * **Taenia solium:** The adult tapeworm resides in the small intestine. While it is large, it lacks the migratory "wandering" tendency of *Ascaris*. Its primary clinical concern (other than intestinal infection) is **Cysticercosis**, where larvae form cysts in the brain (NCC) or muscles, not the bile ducts. **High-Yield Clinical Pearls for NEET-PG:** * **Imaging Gold Standard:** Ultrasound is the investigation of choice for biliary ascariasis, often showing a "tube-like" or "railway track" appearance within the bile duct. * **Loeffler’s Syndrome:** Remember that *Ascaris* causes transient pulmonary eosinophilia during its larval migration phase through the lungs. * **Other Biliary Parasites:** While *Ascaris* is the most common cause of *mechanical* obstruction, **Clonorchis sinensis** and **Fasciola hepatica** are other high-yield parasites associated with biliary disease and cholangiocarcinoma.

Q: Which of the following statements regarding Malaria parasites is correct?

Has man as its intermediate host. **Explanation:** The life cycle of *Plasmodium* (the malaria parasite) involves two hosts: a vertebrate host (human) and an invertebrate host (female *Anopheles* mosquito). **1. Why Option A is Correct:** In parasitology, the **Definitive Host** is where the sexual cycle occurs, and the **Intermediate Host** is where the asexual cycle occurs. * **Sexual Cycle (Sporogony):** Occurs in the female *Anopheles* mosquito (Definitive Host). * **Asexual Cycle (Schizogony):** Occurs in humans (Intermediate Host). Therefore, man is the intermediate host. **2. Why Other Options are Incorrect:** * **Option B:** The life cycle alternates between humans and the **female *Anopheles* mosquito**. The tsetse fly is the vector for African Trypanosomiasis (Sleeping Sickness). * **Option C:** While four species were traditionally taught (*P. falciparum, P. vivax, P. malariae, P. ovale*), there are now **five** important species infecting humans, including ***Plasmodium knowlesi*** (a zoonotic species). * **Option D:** Malaria parasites are **difficult to culture**. While the Trager-Jensen method (1976) allows for the *in vitro* cultivation of *P. falciparum*, it is complex, expensive, and not a routine laboratory procedure. **Clinical Pearls for NEET-PG:** * **Infective form to humans:** Sporozoites (injected by mosquito). * **Infective form to mosquito:** Gametocytes (ingested from human blood). * **Exo-erythrocytic stage:** Absent in *P. falciparum*. * **Hypnozoites (Latent liver stage):** Seen in *P. vivax* and *P. ovale*; responsible for relapses. * **Recrudescence:** Seen in *P. falciparum* and *P. malariae* due to sub-therapeutic treatment or waning immunity.

Q: An AIDS patient presents with headaches and disorientation. A clinical diagnosis of Toxoplasma encephalitis is made, and Toxoplasma cysts are observed in a brain section. Which one of the following antibody results would be most likely in this patient?

IgM nonreactive, IgG reactive (low titre). **Explanation:** The correct answer is **B. IgM nonreactive, IgG reactive (low titre).** **1. Underlying Medical Concept:** In patients with AIDS (typically CD4 <100 cells/mm³), Toxoplasma encephalitis is almost always a result of the **reactivation of a latent infection** rather than a primary (new) infection. * **IgG reactive:** Since the infection is a reactivation, the patient already has pre-existing memory antibodies (IgG). These are often present at low to moderate titers. * **IgM nonreactive:** IgM is a marker of acute, primary infection. In reactivation cases occurring in immunocompromised states, IgM is typically absent. **2. Analysis of Incorrect Options:** * **Option A:** If both are nonreactive, it suggests the patient was never exposed to *Toxoplasma gondii*. While possible, it makes the diagnosis of Toxoplasma encephalitis highly unlikely. * **Options C & D:** High titers of IgG and the presence of IgM are characteristic of **acute primary toxoplasmosis** in an immunocompetent host. In AIDS patients, the immune system is too suppressed to mount a robust IgM response or a significantly high-titer IgG "booster" effect during reactivation. **3. NEET-PG High-Yield Pearls:** * **Most common cause** of CNS mass lesions in AIDS patients is Toxoplasma encephalitis. * **Imaging:** Classic finding on MRI/CT is **multiple ring-enhancing lesions** with a predilection for the basal ganglia. * **Definitive Diagnosis:** Brain biopsy (showing tachyzoites or cysts), though usually diagnosed empirically. * **Treatment:** Pyrimethamine + Sulfadiazine + Leucovorin (Folinic acid). * **Prophylaxis:** Started when CD4 count <100 cells/mm³; drug of choice is **Trimethoprim-Sulfamethoxazole (TMP-SMX)**.

Q: Which of the following is NOT a recognized infectious cause of eosinophilia?

Malaria. **Explanation:** The key to answering this question lies in understanding the host immune response to different types of pathogens. **Eosinophilia** is a hallmark of **helminthic (parasitic worm)** infections, particularly during the tissue-invasive phase of their life cycle [1]. **1. Why Malaria is the Correct Answer:** Malaria is caused by *Plasmodium* species, which are **protozoa**, not helminths. Protozoal infections (like Malaria, Amoebiasis, and Giardiasis) characteristically do **not** cause eosinophilia. Malaria typically presents with anemia, thrombocytopenia, and atypical lymphocytosis, but an elevated eosinophil count should prompt a search for a co-infection. **2. Why the other options are incorrect:** * **Ascaris lumbricoides:** Causes eosinophilia during the **Loeffler’s syndrome** phase, where larvae migrate through the lungs [1]. * **Filariasis:** Caused by *Wuchereria bancrofti*, it is a classic cause of tropical pulmonary eosinophilia (TPE), characterized by extreme elevations in eosinophil counts and IgE [2]. * **Strongyloidiasis:** This helminth can persist for decades in the host via autoinfection; it is a well-known cause of fluctuating or persistent eosinophilia [1]. **High-Yield Clinical Pearls for NEET-PG:** * **NAACP mnemonic** for causes of eosinophilia: **N**eoplasm, **A**llergy/Asthma, **A**ddison’s disease, **C**onnective tissue disorders, and **P**arasites (Helminths). * **Protozoa vs. Helminths:** Remember that protozoa (Malaria, Leishmaniasis, Trypanosomiasis) generally cause **leukopenia or normal counts**, whereas helminths (especially those with a tissue phase) cause **eosinophilia**. * **Exception:** Ectoparasites like Scabies can sometimes cause mild eosinophilia due to allergic sensitization.

Q: Which of the following statements about Giardiasis is FALSE?

Trophozoites have 4 pairs of flagella. ### Explanation **Correct Answer Analysis:** The statement **"Trophozoites have 4 pairs of flagella"** is actually **TRUE**, making it an incorrect choice for a "FALSE" question. However, in the context of many medical entrance exams (including NEET-PG), this question often appears with a technical error in the options or key. Morphologically, *Giardia lamblia* trophozoites are pear-shaped, binucleated, and possess **4 pairs (8 total) of flagella**. *Note: If this was a "Select the False Statement" question, Option A is typically the intended answer in clinical practice, as the Complement Fixation Test (CFT) is not a standard or reliable diagnostic method for Giardiasis.* **Analysis of Other Options:** * **Option B (Stools contain cysts and trophozoites):** This is **TRUE**. In formed stools, cysts are predominantly found, while in acute diarrheal episodes, motile trophozoites can be visualized. * **Option C (Habitat is small intestine):** This is **TRUE**. *Giardia* primarily inhabits the duodenum and upper jejunum. It attaches to the mucosal surface using a ventral sucking disc, leading to malabsorption. * **Option A (Complement fixation test is diagnostic):** This is **FALSE**. Diagnosis relies on stool microscopy (cysts/trophozoites), ELISA for fecal antigens (GSA-65), or the String Test (Entero-test). Serology (like CFT) is rarely used and lacks diagnostic specificity. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Described as "Monkey face" or "Tennis racket" appearance in stained smears. * **Clinical Feature:** Causes **Steatorrhea** (foul-smelling, greasy stools) due to fat malabsorption. It does **not** cause blood in stool (non-invasive). * **Drug of Choice:** Metronidazole or Tinidazole. * **Association:** Increased prevalence in patients with **Common Variable Immunodeficiency (CVID)** or IgA deficiency.

Q: In Plasmodium falciparum, how many cycles does the parasite undergo in the liver?

1. **Explanation:** The correct answer is **B (1)**. In the life cycle of *Plasmodium falciparum*, the parasite undergoes exactly **one cycle** of pre-erythrocytic (exo-erythrocytic) schizogony in the liver. **Why Option B is correct:** When an infected female *Anopheles* mosquito bites a human, it injects sporozoites. These travel to the liver, infect hepatocytes, and multiply to form schizonts. In *P. falciparum* and *P. vivax*, this liver phase occurs only once before the parasites are released into the bloodstream to begin the erythrocytic stage. Once the liver schizont ruptures, the parasites do not re-infect new liver cells. **Why other options are incorrect:** * **Option A (0):** All *Plasmodium* species must undergo an initial liver stage to multiply before they can infect red blood cells. * **Options C & D (2 or 3):** There is no "secondary" liver cycle in *P. falciparum*. While *P. vivax* and *P. ovale* have dormant stages (hypnozoites) that can cause relapses, they still only undergo one initial cycle of development per infection event; the relapse is a delayed activation of that single infection, not a continuous cycling within the liver. **High-Yield Clinical Pearls for NEET-PG:** * **No Hypnozoites:** *P. falciparum* and *P. malariae* do not form hypnozoites; therefore, they **do not relapse**. They may "recrudesce" due to persistent low-level parasitemia in the blood. * **Shortest Incubation:** *P. falciparum* has the shortest pre-erythrocytic cycle (approx. 6 days), leading to a shorter incubation period compared to other species. * **Merozoite Yield:** A single *P. falciparum* sporozoite can produce up to 30,000–40,000 merozoites per liver cell, the highest among all species, contributing to its high pathogenicity.

Q: DEC Provocation test is used for which condition?

Filariasis. **Explanation:** **Diethylcarbamazine (DEC) Provocation Test** is a diagnostic technique used for **Lymphatic Filariasis**, specifically caused by *Wuchereria bancrofti* and *Brugia malayi*. **Why it is the correct answer:** In many endemic areas, microfilariae exhibit **nocturnal periodicity**, meaning they circulate in the peripheral blood only at night (usually between 10 PM and 2 AM). To avoid collecting blood samples at night, a "DEC Provocation Test" is performed. A small dose of DEC (2 mg/kg) is administered to the patient. This drug stimulates the microfilariae to emerge from the deep pulmonary capillaries into the peripheral circulation within 30–60 minutes, allowing for daytime blood collection and diagnosis. **Why other options are incorrect:** * **Malaria:** Diagnosis is primarily via thick and thin peripheral blood smears (Gold Standard) or Rapid Diagnostic Tests (RDTs) detecting PfHRP2 or LDH antigens. * **Guinea Worm (*Dracunculus medinensis*):** Diagnosis is clinical, based on the visualization of the adult worm emerging from a skin ulcer, usually on the lower distal limbs. * **Yellow Fever:** This is a viral hemorrhagic fever diagnosed via Serology (ELISA for IgM) or PCR; it has no relation to microfilariae. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** DEC is the treatment of choice for Filariasis (except in cases of co-infection with Onchocerciasis or Loiasis due to the risk of Mazzotti reaction). * **Contraindication:** DEC provocation should be avoided in patients suspected of having **Loiasis** (*Loa loa*), as it can trigger fatal encephalopathy. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens; DEC is used here both for diagnosis and treatment.

Q: A 6-year-old girl presents with intense perianal itching, especially at night. Physical examination reveals perianal excoriation. An adhesive tape test is positive for worms. Which of the following is the most likely parasite in this patient?

Enterobius vermicularis. **Explanation** The clinical presentation described is a classic case of **Enterobiasis**, caused by **Enterobius vermicularis** (Pinworm or Seatworm). **Why Option C is Correct:** * **Nocturnal Pruritus Ani:** The hallmark symptom is intense perianal itching at night. This occurs because the gravid female worm migrates out of the anus to deposit eggs on the perianal skin folds. * **Adhesive Tape Test (Scotch Tape Test):** This is the gold standard for diagnosis. Since eggs are rarely found in feces, a transparent adhesive tape is applied to the perianal area in the morning to collect and visualize the characteristic **planoconvex (D-shaped)** eggs under a microscope. * **Transmission:** It is common in children due to the feco-oral route and autoinoculation (finger-to-mouth after scratching). **Why Other Options are Incorrect:** * **Options A & D (Hookworms):** *Ancylostoma duodenale* and *Necator americanus* primarily cause iron-deficiency anemia and ground itch at the site of larval penetration (usually the feet). They do not cause perianal itching. * **Option B (Ascaris lumbricoides):** The giant roundworm typically presents with intestinal obstruction, Loeffler’s syndrome (pulmonary phase), or biliary colic. Diagnosis is made by finding eggs in the stool, not via the tape test. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Eggs are non-bile stained and D-shaped. * **Treatment:** **Albendazole** or Mebendazole (single dose, repeated after 2 weeks). It is crucial to **treat the entire family** to prevent reinfection. * **Ectopic Migration:** In females, the worm can migrate into the vagina, leading to vulvovaginitis or pelvic inflammatory disease (PID).

Q: Sleeping sickness is transmitted by which vector?

Tsetse fly. **Explanation:** **Correct Answer: A. Tsetse fly** Sleeping sickness, also known as **African Trypanosomiasis**, is caused by protozoan parasites of the genus *Trypanosoma brucei* (*T.b. gambiense* and *T.b. rhodesiense*). The definitive vector for this disease is the **Tsetse fly** (genus *Glossina*). When an infected fly takes a blood meal, it injects metacyclic trypomastigotes into the host's skin, leading to a systemic infection characterized by fever, lymphadenopathy (Winterbottom’s sign), and eventually CNS involvement (meningoencephalitis). **Why the other options are incorrect:** * **B. House fly (*Musca domestica*):** These are mechanical vectors. They do not support the biological life cycle of parasites but transmit pathogens like *E. coli*, *Shigella*, and various helminth eggs via contaminated feet and mouthparts. * **C. Sand fly (*Phlebotomus*):** This is the vector for **Leishmaniasis** (Kala-azar) and Sandfly fever. It transmits *Leishmania* promastigotes. * **D. Simulium fly (Black fly):** This is the vector for **Onchocerciasis** (River Blindness), transmitting the filarial nematode *Onchocerca volvulus*. **High-Yield Clinical Pearls for NEET-PG:** * **Winterbottom’s Sign:** Posterior cervical lymphadenopathy; a classic clinical sign of African Trypanosomiasis. * **Antigenic Variation:** *Trypanosoma brucei* undergoes **Variant Surface Glycoprotein (VSG)** switching, allowing it to evade the host immune system. * **Drug of Choice:** **Suramin** or **Pentamidine** for early stages; **Melarsoprol** or **Eflornithine** for late-stage CNS involvement. * **Chagas Disease:** Do not confuse with American Trypanosomiasis, which is caused by *T. cruzi* and transmitted by the **Reduviid (Triatomine) bug**.

Question 1

In which host does the flagellar stage of the Leishmania parasite occur?

Accepted Answer

Sandfly

Answer

Man

Answer

Dog

Answer

Hamster

Question 2

Which parasite causes biliary tract obstruction?

Accepted Answer

Ascaris

Answer

Trichinella

Answer

Taenia solium

Answer

All of the above

Question 3

Which of the following statements regarding Malaria parasites is correct?

Accepted Answer

Has man as its intermediate host

Answer

Has a life cycle that alternates between man and tse-tse fly

Answer

Has 4 important species in man

Answer

Can be easily cultured in the laboratory

Question 4

An AIDS patient presents with headaches and disorientation. A clinical diagnosis of Toxoplasma encephalitis is made, and Toxoplasma cysts are observed in a brain section. Which one of the following antibody results would be most likely in this patient?

Accepted Answer

IgM nonreactive, IgG reactive (low titre)

Answer

IgM nonreactive, IgG nonreactive

Answer

IgM reactive (low titer), IgG reactive (high titer)

Answer

IgM reactive (high titer), IgG reactive (high titer)

Question 5

Which of the following is NOT a recognized infectious cause of eosinophilia?

Accepted Answer

Malaria

Answer

Ascaris lumbricoides

Answer

Filariasis

Answer

Strongyloidiasis

Question 6

Which of the following statements about Giardiasis is FALSE?

Accepted Answer

Trophozoites have 4 pairs of flagella

Answer

Complement fixation test is diagnostic

Answer

Stools contain cysts and trophozoites

Answer

Habitat is small intestine

Question 7

In Plasmodium falciparum, how many cycles does the parasite undergo in the liver?

Accepted Answer

1

Answer

0

Answer

2

Answer

3

Question 8

DEC Provocation test is used for which condition?

Accepted Answer

Filariasis

Answer

Malaria

Answer

Guinea worm

Answer

Yellow fever

Question 9

A 6-year-old girl presents with intense perianal itching, especially at night. Physical examination reveals perianal excoriation. An adhesive tape test is positive for worms. Which of the following is the most likely parasite in this patient?

Accepted Answer

Enterobius vermicularis

Answer

Ancylostoma duodenale

Answer

Ascaris lumbricoides

Answer

Necator americanus

Question 10

Sleeping sickness is transmitted by which vector?

Accepted Answer

Tsetse fly

Answer

House fly

Answer

Sand fly

Answer

Simulium fly

Parasitology — MCQs

Parasitology — MCQs

On this page

Practice by Chapter

Want unlimited practice?