Parasitology Practice Questions

Q: Lymphatic obstruction occurs with which of the following parasites?

Filarial worm. **Explanation:** **Correct Option: A. Filarial worm (*Wuchereria bancrofti* / *Brugia malayi*)** Lymphatic filariasis is primarily caused by *Wuchereria bancrofti*. The adult worms reside in the **afferent lymphatic vessels** and lymph nodes. The pathogenesis involves a combination of mechanical obstruction by the adult worms and a profound inflammatory response (Th2-mediated) to the parasite and its endosymbiont, *Wolbachia*. Over time, chronic inflammation leads to **lymphangiosclerosis** and fibrosis, resulting in permanent lymphatic obstruction, lymphoedema, and eventually **Elephantiasis**. **Incorrect Options:** * **B. Hookworm (*Ancylostoma duodenale*):** These reside in the small intestine and feed on blood. They are primarily associated with **Iron Deficiency Anemia** and ground itch, not lymphatic pathology. * **C. Guinea worm (*Dracunculus medinensis*):** The adult female migrates to the subcutaneous tissues (usually of the lower limbs) to create a blister and release larvae. It causes local ulcers and secondary infections but does not obstruct lymphatics. * **D. Pinworm (*Enterobius vermicularis*):** These inhabit the cecum and appendix. The hallmark clinical feature is **perianal pruritus** (nocturnal itching) as the female migrates to the perianal skin to lay eggs. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Culex quinquefasciatus* is the most common vector for *W. bancrofti* in India. * **Nocturnal Periodicity:** Microfilariae appear in the peripheral blood between **10 PM and 2 AM**. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough, wheezing, and high eosinophil counts. * **Drug of Choice:** Diethylcarbamazine (DEC). Note: DEC is contraindicated in Onchocerciasis due to the Mazzotti reaction. * **Diagnostic Gold Standard:** Demonstration of microfilariae in a peripheral blood smear (thick film).

Q: Cutaneous larva currens is a feature of which of the following?

Strongyloides stercoralis. **Explanation:** **Larva currens** is a pathognomonic clinical sign of **Strongyloides stercoralis** infection. It occurs during the autoinfection cycle when filariform larvae penetrate the perianal skin and migrate rapidly through the dermis. The term "currens" (Latin for "running") refers to the exceptionally high speed of migration—up to **5–10 cm per hour**—resulting in a rapidly advancing, pruritic, erythematous, serpiginous wheal. **Analysis of Options:** * **Strongyloides stercoralis (Correct):** Causes Larva currens. It typically presents in the perianal region, buttocks, or trunk. Due to its speed, the lesion changes position visibly within a short period. * **Ancylostoma braziliense & A. caninum (Incorrect):** These are the most common causes of **Cutaneous Larva Migrans (CLM)** or "creeping eruption." Unlike larva currens, CLM moves much slower (about **1–2 cm per day**) and is caused by non-human hookworms that cannot complete their life cycle in humans. * **Loa loa (Incorrect):** This filarial nematode causes **Calabar swellings** (transient localized angioedema) and can be seen migrating across the subconjunctiva of the eye. **High-Yield NEET-PG Pearls:** 1. **Speed is the Key:** Larva currens (cm/hour) vs. Larva migrans (cm/day). 2. **Autoinfection:** *S. stercoralis* is unique because it can complete its entire life cycle within the human host, leading to persistent infections for decades. 3. **Hyperinfection Syndrome:** In immunocompromised patients (especially those on steroids), *S. stercoralis* can lead to fatal disseminated disease. 4. **Treatment:** Ivermectin is the drug of choice for Strongyloidiasis.

Q: A specimen resected from a child with intestinal obstruction is shown. What is the most likely diagnosis?

Ascariasis. ***Ascariasis*** - The specimen shows a **bolus of large roundworms** (Ascaris lumbricoides) causing **mechanical intestinal obstruction**, which is pathognomonic for ascariasis. - This condition is **common in children** in endemic areas and typically presents with intestinal obstruction due to a **tangled mass of adult worms**. *Kala-azar* - This is a **systemic leishmaniasis** that causes hepatosplenomegaly, fever, and pancytopenia, not intestinal obstruction. - The pathology involves **reticuloendothelial system** involvement, not intestinal worm masses. *Meckel's diverticulum* - This congenital anomaly appears as a **small bowel outpouching** containing ectopic gastric or pancreatic tissue. - The specimen would show a **diverticular structure**, not a mass of parasitic worms. *Strongyloidiasis* - Caused by **Strongyloides stercoralis**, which are much **smaller threadlike worms** that don't form obstructing masses. - This parasite typically causes **duodenitis** and **malabsorption**, rarely mechanical obstruction.

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.

Question 1

Lymphatic obstruction occurs with which of the following parasites?

Accepted Answer

Filarial worm

Answer

Hook worm

Answer

Guinea worm

Answer

Pin worm

Question 2

Cutaneous larva currens is a feature of which of the following?

Accepted Answer

Strongyloides stercoralis

Answer

Ancylostoma braziliense

Answer

Ancylostoma caninum

Answer

Loa loa

Question 3

A specimen resected from a child with intestinal obstruction is shown. What is the most likely diagnosis?

Accepted Answer

Ascariasis

Answer

Kala-azar

Answer

Meckel's diverticulum

Answer

Strongyloidiasis

Question 4

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

Accepted Answer

Sandfly

Answer

Man

Answer

Dog

Answer

Hamster

Question 5

Which parasite causes biliary tract obstruction?

Accepted Answer

Ascaris

Answer

Trichinella

Answer

Taenia solium

Answer

All of the above

Question 6

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 7

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 8

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

Accepted Answer

Malaria

Answer

Ascaris lumbricoides

Answer

Filariasis

Answer

Strongyloidiasis

Question 9

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 10

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

Accepted Answer

1

Answer

0

Answer

2

Answer

3

Parasitology — MCQs

Parasitology — MCQs

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