Parasitology Practice Questions

Q: An 8-year-old child presents with crampy abdominal pain, nausea, and mild diarrhea for two weeks. The day before the visit, a cylindrical white worm, approximately 30 cm in length, was vomited and preserved. What is the most likely mode of acquisition for this organism?

Ingestion of eggs from human feces. **Explanation:** The clinical presentation of a large (30 cm), cylindrical white worm being vomited is pathognomonic for **Ascaris lumbricoides** (Giant Roundworm). Ascariasis is the most common helminthic infection worldwide. **1. Why Option D is Correct:** *Ascaris lumbricoides* is a soil-transmitted helminth. The life cycle begins when an infected human defecates in the soil. The eggs must undergo a period of maturation (embryonation) in the soil for 2–3 weeks to become infective. Humans acquire the infection via the **fecal-oral route** by ingesting these embryonated eggs from contaminated soil, food, or water. Since humans are the only reservoir, the eggs originate from human feces. **2. Why Other Options are Incorrect:** * **Option A (Autoinfection):** This is characteristic of *Strongyloides stercoralis* or *Enterobius vermicularis*. *Ascaris* eggs require time in the soil to become infective and cannot cause immediate autoinfection. * **Option B (Ingestion of cysts):** This is the mode of transmission for protozoa like *Giardia lamblia* or *Entamoeba histolytica*, not large nematodes. * **Option C (Infected pet):** While *Toxocara canis* (dog roundworm) is acquired from pets, it causes Visceral Larva Migrans in humans; the adult worms do not develop in the human intestine and are not vomited. **Clinical Pearls for NEET-PG:** * **Löffler Syndrome:** Pulmonary phase of *Ascaris* migration characterized by eosinophilic pneumonia, cough, and wheezing. * **Complications:** Intestinal obstruction (at the ileocecal valve), biliary colic, or pancreatitis due to worm migration. * **Diagnosis:** Stool microscopy for bile-stained, mamillated eggs. * **Treatment:** Albendazole (400 mg single dose) is the drug of choice.

Q: Which of the following diseases is NOT transmitted by hard ticks?

Relapsing fever. **Explanation:** The correct answer is **Relapsing fever**. In medical parasitology, it is crucial to distinguish between diseases transmitted by **Hard ticks (Ixodidae)** and **Soft ticks (Argasidae)**. 1. **Why Relapsing Fever is the correct answer:** Relapsing fever exists in two forms: **Epidemic** (transmitted by body lice) and **Endemic** (transmitted by **Soft ticks** of the genus *Ornithodoros*). Both are caused by *Borrelia* species. Since it is transmitted by soft ticks, it is not associated with hard ticks. 2. **Analysis of Incorrect Options:** * **Hemorrhagic fever:** Specifically, **Crimean-Congo Hemorrhagic Fever (CCHF)** is a viral disease transmitted primarily by *Hyalomma* ticks (a genus of hard ticks). Kyasanur Forest Disease (KFD) is also transmitted by hard ticks (*Haemaphysalis*). * **Tick typhus:** Also known as Indian Tick Typhus (caused by *Rickettsia conorii*), it is transmitted by hard ticks like *Rhipicephalus sanguineus*. * **Tularemia:** Caused by *Francisella tularensis*, this zoonosis can be transmitted by various routes, but hard ticks (*Dermacentor* and *Amblyomma*) are major biological vectors. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Hard Tick diseases:** "**I**ndian **T**ick **T**yphus, **K**FD, **B**abesiosis, **T**ularemia, **B**ull’s eye rash (Lyme), **C**CHF" (**I T**ake **K**ids **B**ack **T**o **B**ig **C**ities). * **Soft Tick (Argasidae):** Primarily transmits **Endemic Relapsing Fever** (*Borrelia duttoni*). * **Hard Tick (Ixodidae):** Characterized by a dorsal **scutum**, anterior capitulum, and slow feeding (days). * **Lyme Disease:** Transmitted by *Ixodes* (Hard tick); look for Erythema Chronicum Migrans in clinical vignettes.

Q: Barrel-shaped eggs are seen in which of the following parasites?

Whipworm. **Explanation:** The correct answer is **Whipworm (*Trichuris trichiura*)**. **1. Why Whipworm is correct:** The eggs of *Trichuris trichiura* possess a highly characteristic morphology often described as **barrel-shaped**, lemon-shaped, or tea-tray shaped. Key diagnostic features include a thick, smooth brown shell (bile-stained) and the presence of **prominent clear mucoid bipolar plugs** at both ends. These eggs are unembryonated when passed in feces. **2. Why other options are incorrect:** * **Hookworm (*Ancylostoma duodenale/Necator americanus*):** Eggs are oval or elliptical, colorless (non-bile stained), and surrounded by a thin, transparent hyaline shell. They typically contain a segmented ovum (usually 4–8 blastomeres) with a clear space between the shell and the embryo. * **Pinworm (*Enterobius vermicularis*):** Eggs are characterized by a unique **planoconvex** shape (one side flattened, the other convex), resembling the letter ‘D’. They are non-bile stained and contain a fully formed tadpole-like larva. * **Roundworm (*Ascaris lumbricoides*):** Fertilized eggs are typically round or oval with a thick, lumpy, outer **mammillated (albuminous) coat** stained golden-brown by bile. **3. NEET-PG Clinical Pearls:** * **Habitat:** *Trichuris trichiura* lives in the **caecum** and large intestine. * **Clinical Presentation:** Heavy infestation in children can lead to **rectal prolapse** due to mucosal irritation and increased peristalsis. * **Morphology:** The adult worm has a thin, thread-like anterior end and a thick posterior end, resembling a whip. * **Treatment:** Albendazole or Mebendazole are the drugs of choice.

Q: A stool examination reveals acid-fast organisms with oocytes measuring 5 micrometers, causing diarrhea in an HIV-positive patient. What is the causative organism?

Cryptosporidium. ### Explanation The correct answer is **Cryptosporidium parvum**. This is a classic presentation of opportunistic diarrhea in immunocompromised patients, particularly those with HIV/AIDS. #### Why Cryptosporidium is Correct: 1. **Size:** The oocysts of *Cryptosporidium* are characteristically small, measuring **4–6 µm** (average 5 µm). This is the most defining morphological feature in the question. 2. **Staining:** It is an **acid-fast** organism. On Modified Ziehl-Neelsen (kinyoun) stain, they appear as bright red, spherical bodies against a blue/green background. 3. **Clinical Context:** It is a leading cause of chronic, voluminous, watery diarrhea in HIV patients with CD4 counts <200 cells/mm³. #### Why Other Options are Incorrect: * **Isospora belli (Cystoisospora):** While also acid-fast and common in HIV, its oocysts are much larger (**25–30 µm**) and typically **ellipsoidal/oval** in shape. * **Microsporidia:** These are the smallest (1–3 µm). Crucially, they are **not** typically identified by standard acid-fast staining; they require specialized stains like Chromotrope 2R or Calcofluor White. * **Blastocystis hominii:** This is a polymorphic protozoan (often seen in vacuolar form). It is **not acid-fast** and its role as a primary pathogen is often debated. #### NEET-PG High-Yield Pearls: * **Morphology Trick:** Remember the "Rule of Sizes" for acid-fast oocysts: *Cryptosporidium* (5 µm) < *Cyclospora* (10 µm) < *Isospora* (25 µm). * **Diagnosis:** Stool examination using **Modified Acid-Fast stain** is the gold standard. * **Treatment:** In HIV patients, the most effective treatment is **HAART** (to restore CD4 count). **Nitazoxanide** is the drug of choice in immunocompetent patients. * **Transmission:** Frequently associated with waterborne outbreaks due to its resistance to chlorination.

Q: Which of the following is NOT transmitted by Aedes mosquitoes?

Malaria. **Explanation:** The correct answer is **Malaria**. This question tests the fundamental knowledge of vector-borne diseases, specifically distinguishing between viral and protozoal transmission cycles. **1. Why Malaria is the Correct Answer:** Malaria is caused by protozoan parasites of the genus *Plasmodium*. It is exclusively transmitted by the bite of an infected **female Anopheles mosquito**, not *Aedes*. The life cycle of the malaria parasite involves a sexual cycle in the Anopheles mosquito (definitive host) and an asexual cycle in humans (intermediate host). **2. Why the other options are incorrect:** * **Chikungunya, Zika, and Dengue** are all viral infections (Arboviruses) primarily transmitted by **Aedes aegypti** and **Aedes albopictus**. * These mosquitoes are "day-biters" and typically breed in clean, stagnant water (e.g., flower pots, discarded tires). **Clinical Pearls for NEET-PG:** * **Aedes Mosquito:** Known as the "Tiger Mosquito" due to white stripes on its body. It is the vector for Dengue, Chikungunya, Zika, Yellow Fever, and Rift Valley Fever. * **Dengue:** Look for "break-bone fever" and retro-orbital pain in clinical vignettes. * **Zika:** High-yield association with **Microcephaly** in newborns and **Guillain-Barré Syndrome** in adults. * **Chikungunya:** Characterized by severe, often persistent, debilitating joint pain (arthritis). * **Malaria Vector:** *Anopheles stephensi* is the primary urban malaria vector in India, while *Anopheles culicifacies* is the major rural vector.

Q: Cutaneous larva migrans is caused by which organism?

Ancylostoma braziliense. **Explanation:** **Cutaneous Larva Migrans (CLM)**, also known as "creeping eruption," is a zoonotic infection caused by the larvae of animal hookworms. 1. **Why Ancylostoma braziliense is correct:** The most common cause of CLM is **Ancylostoma braziliense** (the hookworm of cats and dogs). When humans come into contact with soil contaminated by animal feces, the filariform larvae penetrate the skin. Because humans are accidental, non-definitive hosts, the larvae lack the enzymes (collagenases) necessary to penetrate the basement membrane and reach the circulation. Consequently, they remain trapped in the epidermis, migrating aimlessly and creating characteristic **serpiginous, erythematous, pruritic tracks.** 2. **Why the other options are incorrect:** * **Anisakis simplex:** Causes **Anisakiasis**, a gastrointestinal infection acquired by consuming raw or undercooked seafood containing the larvae. * **Toxocara species:** Causes **Visceral Larva Migrans (VLM)** and **Ocular Larva Migrans (OLM)**. Unlike CLM, these larvae migrate through deeper internal organs (liver, lungs, eyes) because they are ingested rather than penetrating the skin. * **Necator americanus:** This is a human hookworm. While it can cause a transient "ground itch" at the site of entry, it successfully penetrates the dermis to complete its life cycle in the human intestine, rather than remaining confined to the skin as a migrating larva. **High-Yield NEET-PG Pearls:** * **Clinical Presentation:** Intensely itchy, snake-like tracks, most commonly on the feet (sand-box exposure). * **Treatment of Choice:** Topical or oral **Albendazole** or **Ivermectin**. * **Key Distinction:** CLM = *Ancylostoma braziliense* (Skin); VLM = *Toxocara canis* (Viscera). * **Larva Currens:** A similar but much faster-moving eruption caused by *Strongyloides stercoralis*.

Q: A HIV-positive individual has diarrheal episodes. Stool examination reveals oocysts of size 8-10 microns. What is the most likely diagnosis?

Cyclospora. ### **Explanation** The clinical presentation of chronic diarrhea in an HIV-positive patient points toward opportunistic coccidian parasites. The definitive diagnostic feature in this question is the **size of the oocyst (8–10 µm).** **1. Why Cyclospora is Correct:** * **Cyclospora cayetanensis** produces spherical oocysts that measure **8–10 µm** in diameter. * They are acid-fast (variable) and typically appear as "wrinkled" spheres. * In HIV patients, they cause prolonged, watery diarrhea similar to Cryptosporidium but are distinguished primarily by their larger size. **2. Why Other Options are Incorrect:** * **Cryptosporidium parvum:** This is the most common cause of diarrhea in AIDS patients, but its oocysts are significantly smaller, measuring **4–6 µm**. * **Isospora (Cystoisospora) belli:** These oocysts are much larger (**25–30 µm**) and have a characteristic elliptical/oval shape, unlike the spherical shape of Cyclospora. * **Cryptococcus:** This is a fungus, not a coccidian parasite. While it can cause disseminated disease in HIV, it typically presents as meningitis and is identified by India Ink staining of CSF, not as oocysts in stool. **3. High-Yield Clinical Pearls for NEET-PG:** * **Size Comparison (The "Rule of 5s"):** * *Cryptosporidium:* ~5 µm (Smallest) * *Cyclospora:* ~10 µm (Double the size of Cryptosporidium) * *Isospora:* ~25–30 µm (Largest, oval) * **Autofluorescence:** *Cyclospora* oocysts exhibit blue-green autofluorescence under UV microscopy, a key diagnostic feature. * **Staining:** All three (Cryptosporidium, Cyclospora, Isospora) are **Modified Acid-Fast positive**. * **Treatment:** While *Cryptosporidium* is difficult to treat (Nitazoxanide), both *Cyclospora* and *Isospora* respond well to **Cotrimoxazole (TMP-SMX)**.

Q: Erythrocytic schizogony of Plasmodium liberates which stage?

Merozoites. **Explanation:** The life cycle of *Plasmodium* involves two distinct phases of asexual reproduction (schizogony) in the human host: the **Exo-erythrocytic stage** (liver) and the **Erythrocytic stage** (RBCs). In the erythrocytic stage, a merozoite infects a red blood cell, matures into a ring-form **trophozoite**, and then develops into a **schizont**. When the schizont matures, the RBC ruptures, liberating a new generation of **merozoites** into the bloodstream. These released merozoites then infect fresh RBCs, repeating the cycle. The clinical paroxysm (fever and chills) in malaria coincides with this synchronous rupture of RBCs and the release of merozoites and metabolic byproducts. **Analysis of Options:** * **A. Sporozoites:** These are the infective forms of the parasite. They are inoculated into the human host by the bite of an infected female *Anopheles* mosquito. * **B. Trophozoites:** This is the active, feeding stage of the parasite *inside* the RBC. It does not represent the stage liberated upon schizogony; rather, it matures into the schizont. * **D. Phanerozoites:** This term refers to the exo-erythrocytic stages found in the tissues (liver) of birds/animals in certain species. In humans, the equivalent is the pre-erythrocytic schizont. **High-Yield Clinical Pearls for NEET-PG:** * **Hypnozoites:** These are dormant liver stages found only in *P. vivax* and *P. ovale*, responsible for **relapses**. * **Recrudescence:** Seen in *P. falciparum* and *P. malariae* due to the persistence of low-level parasitemia in the blood (not liver). * **Schüffner’s dots:** Seen in RBCs infected with *P. vivax* and *P. ovale*. * **Maurer’s clefts:** Seen in RBCs infected with *P. falciparum*.

Q: In malaria, where does the sexual cycle occur?

Gametocytes to sporozoites. **Explanation:** The life cycle of *Plasmodium* involves two hosts: humans (intermediate host) and the female *Anopheles* mosquito (definitive host). **1. Why Option B is Correct:** The **sexual cycle (Sporogony)** occurs entirely within the mosquito. It begins when the mosquito ingests male and female **gametocytes** from an infected human. In the mosquito's gut, these mature into gametes, undergo fertilization to form a zygote (ookinete), and eventually produce thousands of **sporozoites** (the infective stage for humans). Thus, the transition from gametocytes to sporozoites represents the completion of the sexual phase. **2. Analysis of Incorrect Options:** * **Option A (Sporozoites to gametocytes):** This represents the **asexual cycle (Schizogony)** which occurs in humans. It includes the exo-erythrocytic (liver) and erythrocytic (RBC) stages. * **Option C (Occurs in humans):** Humans host the asexual cycle only. The sexual cycle requires the cooler body temperature and specific physiological environment of the mosquito. * **Option D (Responsible for relapse):** Relapse is caused by **hypnozoites** (dormant liver stages), specifically seen in *P. vivax* and *P. ovale*. This is a feature of the asexual cycle, not the sexual cycle. **Clinical Pearls for NEET-PG:** * **Definitive Host:** Female *Anopheles* mosquito (where sexual fusion occurs). * **Intermediate Host:** Humans (where asexual multiplication occurs). * **Infective form to humans:** Sporozoites (found in mosquito salivary glands). * **Infective form to mosquito:** Gametocytes (found in human peripheral blood). * **Exflagellation:** This process refers to the formation of male microgametes in the mosquito's midgut—a high-yield term often associated with the sexual cycle.

Question 1

An 8-year-old child presents with crampy abdominal pain, nausea, and mild diarrhea for two weeks. The day before the visit, a cylindrical white worm, approximately 30 cm in length, was vomited and preserved. What is the most likely mode of acquisition for this organism?

Accepted Answer

Ingestion of eggs from human feces

Answer

Autoinfection

Answer

Ingestion of cysts in contaminated water

Answer

Ingestion of eggs from an infected pet

Question 2

Which of the following diseases is NOT transmitted by hard ticks?

Accepted Answer

Relapsing fever

Answer

Hemorrhagic fever

Answer

Tick typhus

Answer

Tularemia

Question 3

Barrel-shaped eggs are seen in which of the following parasites?

Accepted Answer

Whipworm

Answer

Hookworm

Answer

Pinworm

Answer

Roundworm

Question 4

A stool examination reveals acid-fast organisms with oocytes measuring 5 micrometers, causing diarrhea in an HIV-positive patient. What is the causative organism?

Accepted Answer

Cryptosporidium

Answer

Isospora belli

Answer

Microsporidia

Answer

Blastocystis hominii

Question 5

Which of the following is NOT transmitted by Aedes mosquitoes?

Accepted Answer

Malaria

Answer

Chikungunya

Answer

Zika

Answer

Dengue

Question 6

Cutaneous larva migrans is caused by which organism?

Accepted Answer

Ancylostoma braziliense

Answer

Anisakis simplex

Answer

Toxocara species

Answer

Necator americanus

Question 7

A HIV-positive individual has diarrheal episodes. Stool examination reveals oocysts of size 8-10 microns. What is the most likely diagnosis?

Accepted Answer

Cyclospora

Answer

Cryptococcus

Answer

Cryptosporidium parvum

Answer

Isospora

Question 8

Erythrocytic schizogony of Plasmodium liberates which stage?

Accepted Answer

Merozoites

Answer

Sporozoites

Answer

Trophozoites

Answer

Phanerozoites

Question 9

In malaria, where does the sexual cycle occur?

Accepted Answer

Gametocytes to sporozoites

Answer

Sporozoites to gametocytes

Answer

Occurs in humans

Answer

Responsible for relapse

Question 10

Which of the following statements is FALSE regarding filariasis?

Accepted Answer

Humoral immunity plays a dominant role

Answer

Morbidity increases with age in endemic areas

Answer

It is usually unilateral

Answer

Man is the only host for filariasis

Parasitology — MCQs

Parasitology — MCQs

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