Parasitology Practice Questions

Q: A 40-year-old patient developed a sudden onset of high fever. Peripheral blood film examination showed malaria parasite pigment that was yellowish-brown, and the schizonts measured 9-10 microns and contained 20 merozoites each. Which Plasmodium species is most likely responsible?

Plasmodium vivax. ### Explanation The correct answer is **Plasmodium vivax**. This diagnosis is based on the specific morphology of the schizont and the characteristics of the malarial pigment. **1. Why Plasmodium vivax is correct:** * **Schizont Size:** *P. vivax* schizonts are large, typically measuring **9–10 microns**, almost filling the enlarged infected erythrocyte. * **Merozoite Count:** They contain **12–24 merozoites** (average 16–20), which matches the 20 merozoites mentioned in the question. * **Pigment:** The malarial pigment (hemozoin) in *P. vivax* is typically **yellowish-brown** and fine. **2. Why other options are incorrect:** * **P. falciparum:** Schizonts are rarely seen in peripheral blood (due to sequestration). When present, they are smaller (approx. 8 microns) and contain **8–36 merozoites** with a single mass of dark pigment. * **P. malariae:** The schizont is smaller (6.5–7 microns) and contains fewer merozoites (**6–12**), often arranged in a characteristic **"Rosette" or "Daisy-head" pattern**. The pigment is dark brown/black. * **P. ovale:** While it has a similar merozoite count to *P. vivax* (average 8–10, up to 12), the infected RBC is typically oval with **fimbriated edges**, and the schizont is smaller (approx. 6 microns). **High-Yield Clinical Pearls for NEET-PG:** * **Schüffner’s dots:** Seen in *P. vivax* and *P. ovale*. * **Ziemann’s dots:** Seen in *P. malariae*. * **Maurer’s clefts:** Seen in *P. falciparum*. * **Relapse:** Occurs in *P. vivax* and *P. ovale* due to dormant **hypnozoites** in the liver (treated with Primaquine). * **Recrudescence:** Occurs in *P. falciparum* and *P. malariae* due to the persistence of erythrocytic stages.

Q: Which is the only living part of a Hydatid cyst?

Germinal epithelium. ### Explanation A Hydatid cyst, caused by the larval stage of ***Echinococcus granulosus***, consists of three distinct layers. Understanding these layers is crucial for identifying the biological activity of the parasite. **1. Why Germinal Epithelium is Correct:** The **Germinal layer (Endocyst)** is the innermost layer of the cyst wall. It is the **only metabolically active and living component** of the parasite. It is responsible for: * Secretory functions (producing the hydatid fluid). * Asexual reproduction (forming brood capsules and scolices). * Formation of the outer laminated membrane. **2. Why the other options are incorrect:** * **Adventitia (Pericyst):** This is the outermost layer, formed by the **host’s inflammatory response** (fibrous tissue). It is not part of the parasite itself. * **Laminated membrane (Ectocyst):** This is the middle, acellular, white chitinous layer. While it provides structural support and protects the parasite from the host's immune system, it is **non-living**. * **Parenchyma of the organ:** This refers to the host tissue (e.g., liver or lung) surrounding the cyst, not a component of the cyst wall. ### NEET-PG High-Yield Pearls: * **Hydatid Sand:** Refers to the sediment found in the cyst fluid, consisting of free scolices, brood capsules, and hooklets. * **Casoni Test:** An immediate hypersensitivity skin test (historically used, now largely replaced by serology/imaging). * **Water Lily Sign:** Seen on imaging when the endocyst ruptures and the membranes float in the fluid. * **Surgical Caution:** During surgery (PAIR technique), scolicidal agents (e.g., hypertonic saline) are used to kill the germinal layer and prevent secondary hydatidosis or anaphylaxis due to spillage.

Q: A patient presents with diarrhea. Analysis of stool on wet mount shows mobile protozoa without RBCs and pus cells. What is the most likely diagnosis?

Giardiasis. ### Explanation The correct answer is **Giardiasis**. **Why Giardiasis is correct:** The clinical presentation of diarrhea with a stool wet mount showing **mobile protozoa** but **no RBCs or pus cells** is characteristic of *Giardia lamblia*. Giardia is a non-invasive parasite that colonizes the duodenum and upper jejunum. Because it does not invade the intestinal mucosa or cause ulceration, it results in **non-inflammatory diarrhea** (steatorrhea). Therefore, the stool typically lacks inflammatory markers like Red Blood Cells (RBCs) and pus cells (leukocytes). On a wet mount, the trophozoites exhibit a characteristic "falling leaf" motility. **Analysis of Incorrect Options:** * **Entamoeba histolytica:** This is an invasive parasite that causes amoebic dysentery. It produces "flask-shaped ulcers," leading to the presence of **RBCs (erythrophagocytosis)** and cellular debris in the stool. * **Balantidium coli:** This is the largest protozoan infecting humans and is invasive. It causes mucosal ulceration similar to *E. histolytica*, typically resulting in blood and mucus in the stool. * **Trichomonas hominis:** While found in the human colon as a commensal and possessing motility, it is generally considered non-pathogenic and is not a primary cause of clinical diarrhea. **NEET-PG High-Yield Pearls:** * **Motility:** *Giardia* = Falling leaf motility; *Balantidium* = Boring/Rotary motility; *E. histolytica* = Purposeful/Unidirectional pseudopodial motility. * **Stool Microscopy:** *Giardia* is associated with malabsorption and fatty stools (steatorrhea). * **Drug of Choice:** Metronidazole is the treatment of choice for Giardiasis, though Tinidazole is often preferred for its single-dose efficacy. * **String Test (Entero-test):** A classic diagnostic method used for *Giardia* and *Strongyloides* when stool exams are negative.

Q: What is the primary habitat of hookworm?

Jejunum. **Explanation:** The primary habitat of hookworms (*Ancylostoma duodenale* and *Necator americanus*) is the **upper part of the small intestine**, specifically the **jejunum** (and occasionally the distal duodenum). 1. **Why Jejunum is Correct:** Hookworms are hematophagous parasites that attach to the intestinal mucosa using their buccal capsules (teeth or cutting plates). The jejunum provides an ideal environment due to its extensive surface area and rich vascularity, which facilitates the parasite's blood-feeding requirements. While they pass through the duodenum, the majority of the adult worm burden resides in the proximal jejunum. 2. **Analysis of Incorrect Options:** * **Duodenum:** Although *Ancylostoma duodenale* is named after the duodenum, it is primarily found in the distal duodenum and proximal jejunum. In multiple-choice questions where both are listed, the **jejunum** is considered the definitive primary habitat. * **Ileum:** This is the primary habitat for other parasites like *Giardia lamblia* (distal part) or the site of Vitamin B12 absorption, but it is too distal for the primary concentration of hookworms. * **Colon:** This is the habitat for parasites like *Entamoeba histolytica*, *Trichuris trichiura* (whipworm), and *Enterobius vermicularis* (pinworm). **High-Yield Clinical Pearls for NEET-PG:** * **Infective Stage:** Filariform larva (penetrates intact skin, usually the foot). * **Diagnostic Stage:** Non-bile stained, segmented eggs in feces. * **Pathogenesis:** The primary complication is **Iron Deficiency Anemia** (Microcytic Hypochromic) due to chronic blood loss. *A. duodenale* causes more blood loss (~0.15 ml/day) than *N. americanus* (~0.03 ml/day). * **Ground Itch:** A pruritic dermatitis at the site of larval entry. * **Loeffler’s Syndrome:** Transient pulmonary symptoms during the larval migratory phase through the lungs.

Q: Senescent red blood cells are primarily attacked in which type of malaria?

Quartan malaria. **Explanation:** The preference of *Plasmodium* species for specific ages of red blood cells (RBCs) is a high-yield concept in parasitology. **1. Why Option D is Correct:** **Quartan malaria**, caused by ***Plasmodium malariae***, has a unique predilection for **senescent (old) erythrocytes**. Because the population of aging RBCs in the peripheral blood is relatively small, the parasitemia levels in *P. malariae* infections remain low (usually <1%). This species is also characterized by a 72-hour erythrocytic cycle, leading to paroxysms every fourth day. **2. Why Other Options are Incorrect:** * **Options A & B (P. vivax and P. ovale):** These species selectively infect **young RBCs (reticulocytes)**. They utilize the Duffy blood group antigen (specifically *P. vivax*) to invade immature cells. Since reticulocytes comprise only about 1–2% of total RBCs, parasitemia is limited. * **Option C (P. falciparum):** This is the most "promiscuous" species; it invades **RBCs of all ages** (young, mature, and old). This leads to high levels of parasitemia and the severe clinical manifestations associated with malignant tertian malaria. **NEET-PG High-Yield Pearls:** * **P. falciparum:** All ages of RBCs; highest parasitemia; "Maurer’s clefts." * **P. vivax/ovale:** Reticulocytes; "Schüffner’s dots"; presence of hypnozoites (relapse). * **P. malariae:** Old RBCs; "Ziemann’s dots"; characteristic "Band form" trophozoites. * **P. knowlesi:** All ages of RBCs; 24-hour cycle (quotidian fever).

Q: Enterobius commonly inhabit which part of the gastrointestinal tract?

Caecum. **Explanation:** *Enterobius vermicularis* (Pinworm or Seatworm) is a nematode that primarily inhabits the **caecum and the adjacent parts of the large intestine** (ascending colon and appendix). After the ingestion of embryonated eggs, the larvae hatch in the duodenum and migrate down the gastrointestinal tract. They reach maturity in the caecum, where the adult worms attach to the mucosal surface. **Why the other options are incorrect:** * **Duodenum (A):** This is the site where the larvae hatch from the eggs, but they do not remain here to mature or reside as adults. * **Jejunum (B) and Ileum (C):** While the larvae pass through the small intestine during their downward migration, these are not the definitive habitats for adult *Enterobius*. The small intestine is the primary habitat for other nematodes like *Ascaris lumbricoides* and *Giardia* (duodenum/jejunum). **NEET-PG High-Yield Pearls:** * **Nocturnal Migration:** Gravid female worms migrate out through the anus at night to deposit eggs on the perianal skin, causing the hallmark symptom: **Pruritus ani**. * **Diagnosis:** The investigation of choice is the **NIH Swab** or **Scotch Tape (Cellophane Tape) test**, performed early in the morning before bathing. Eggs are rarely found in routine stool examinations. * **Retroinfection:** Larvae may hatch on the perianal skin and migrate back into the colon. * **Treatment:** Albendazole or Mebendazole is the drug of choice. It is crucial to **treat the entire family** simultaneously to prevent reinfection.

Q: Identify the microorganism shown in the image.

Entamoeba histolytica. ***Entamoeba histolytica*** - The image displays the **trophozoite** stage, characterized by a single nucleus with a central, dot-like **karyosome**. - A key diagnostic feature seen here is the presence of ingested **red blood cells** within the cytoplasm, a phenomenon known as **erythrophagocytosis**, which indicates invasive disease. *Giardia lamblia* - *Giardia* trophozoites are pear-shaped and **binucleated**, often described as having a face-like appearance, which is distinct from the single nucleus seen in the image. - They are flagellated protozoa and do not phagocytose red blood cells. *Shigella dysenteriae* - *Shigella* is a **bacterium**, not a protozoan, and would appear as a small, rod-shaped organism under a microscope. - It lacks the complex eukaryotic structures, such as a distinct nucleus and cytoplasmic inclusions, that are visible in the provided image. *Campylobacter jejuni* - This is a **bacterium** known for its characteristic curved, S-shaped, or "gull-wing" morphology. - As a prokaryote, it is much smaller and structurally simpler than the large amoeboid parasite shown.

Q: A girl, after returning from a picnic, complains of pain in her eyes. She had not maintained proper hygiene of her contact lenses. What would be the cause?

Acanthamoeba. ***Acanthamoeba*** - **Acanthamoeba** is a free-living amoeba commonly found in water sources (tap water, lakes, swimming pools) and soil. - Poor contact lens hygiene, such as rinsing lenses or storing them in non-sterile solutions (like tap water, which might be encountered during a picnic or travel hygiene lapse), is a key risk factor for **Acanthamoeba keratitis (AK)**. - AK is characterized by severe ocular pain, often disproportionate to the clinical findings, and can lead to a pathognomonic **ring-shaped corneal infiltrate**. - The combination of **outdoor water exposure + contact lens use + poor hygiene** strongly suggests Acanthamoeba. *Pseudomonas aeruginosa* - **Pseudomonas aeruginosa** is the most common cause of **bacterial keratitis** in contact lens users, especially with improper hygiene. - It typically causes rapidly progressive, purulent corneal ulceration with a characteristic greenish discharge. - While very common in contact lens wearers, the clinical picture here (picnic setting with potential water exposure) more specifically points to a protozoal etiology. *Herpes simplex virus* - **Herpes simplex virus (HSV)** causes recurrent viral keratitis, typically presenting with characteristic **dendritic ulcers** on the cornea. - HSV transmission is via contact with infected bodily fluids or reactivation of latent virus, not through contact lens solution contamination. *Fusarium* - **Fusarium** is a fungus that can cause fungal keratitis in contact lens wearers, particularly with exposure to organic matter or contaminated lens solutions. - Fungal keratitis tends to have a more indolent course with feathery, elevated stromal infiltrates. - While possible in contact lens users, the specific epidemiological context and clinical pattern here favor Acanthamoeba over Fusarium.

Q: A HIV-positive patient presents with chronic diarrhoea for 4 weeks. Stool microscopy shows oval/ elliptical cysts measuring 16 X 20 μm. Diagnosis is?

Cystoisospora. ***Cystoisospora*** - The finding of large, oval/ellipsoidal oocysts (typically **20-33 μm** long, range includes the 16 x 20 μm given) in the stool of an HIV patient with chronic diarrhea is diagnostic of **Cystoisospora belli** infection. - *Cystoisospora* causes chronic, profuse watery diarrhea in immunocompromised hosts (like those with **AIDS**) and is effectively treated with **trimethoprim-sulfamethoxazole (TMP-SMX)**. *Cryptosporidium* - This parasite is characterized by small, **spherical oocysts** measuring only **4–6 μm** in diameter, which is much smaller than the size reported (16 x 20 μm). - While *Cryptosporidium* is a common cause of chronic diarrhea in AIDS, the oocyst morphology does not match the description. *Cryptococcus* - **Cryptococcus** is a fungal pathogen (*C. neoformans*) primarily known for causing **meningoencephalitis** in HIV patients, not typically large oval/elliptical oocysts in stool causing chronic primary diarrhea. - Diagnosis relies on visualization of encapsulated yeast in CSF (e.g., **India ink stain**) or **cryptococcal antigen (CrAg)** testing. *Cyclospora* - *Cyclospora cayetanensis* oocysts are medium-sized and **spherical**, typically measuring **8–10 μm** in diameter. - Although it causes prolonged diarrhea in immunocompromised individuals, the oocyst shape (**oval/elliptical**) and size (16 x 20 μm) clearly distinguish it from *Cyclospora*.

Question 1

A 40-year-old patient developed a sudden onset of high fever. Peripheral blood film examination showed malaria parasite pigment that was yellowish-brown, and the schizonts measured 9-10 microns and contained 20 merozoites each. Which Plasmodium species is most likely responsible?

Accepted Answer

Plasmodium vivax

Answer

Plasmodium falciparum

Answer

Plasmodium malariae

Answer

Plasmodium ovale

Question 2

Which is the only living part of a Hydatid cyst?

Accepted Answer

Germinal epithelium

Answer

Adventitia

Answer

Laminated membrane

Answer

Parenchyma of the organ

Question 3

A patient presents with diarrhea. Analysis of stool on wet mount shows mobile protozoa without RBCs and pus cells. What is the most likely diagnosis?

Accepted Answer

Giardiasis

Answer

Balantidium coli

Answer

Trichomonas hominis

Answer

Entamoeba histolytica

Question 4

What is the primary habitat of hookworm?

Accepted Answer

Jejunum

Answer

Ileum

Answer

Colon

Answer

Duodenum

Question 5

Senescent red blood cells are primarily attacked in which type of malaria?

Accepted Answer

Quartan malaria

Answer

Vivax malaria

Answer

Ovale malaria

Answer

Falciparum malaria

Question 6

A 20-year-old female presents with hepatosplenomegaly, fever, pallor, and generalized lymphadenopathy. Which laboratory tests are useful for diagnosis?

Accepted Answer

ESR, Electrophoresis, ELISA

Answer

ESR, Electrophoresis, Parasite detection

Answer

Parasite detection, ELISA, Routine haemogram

Answer

ESR, Parasite detection, ELISA

Question 7

Enterobius commonly inhabit which part of the gastrointestinal tract?

Accepted Answer

Caecum

Answer

Duodenum

Answer

Jejunum

Answer

Ileum

Question 8

Identify the microorganism shown in the image.

Accepted Answer

Entamoeba histolytica

Answer

Giardia lamblia

Answer

Campylobacter jejuni

Answer

Shigella dysenteriae

Question 9

A girl, after returning from a picnic, complains of pain in her eyes. She had not maintained proper hygiene of her contact lenses. What would be the cause?

Accepted Answer

Acanthamoeba

Answer

Pseudomonas aeruginosa

Answer

Herpes simplex virus

Answer

Fusarium

Question 10

A HIV-positive patient presents with chronic diarrhoea for 4 weeks. Stool microscopy shows oval/ elliptical cysts measuring 16 X 20 μm. Diagnosis is?

Accepted Answer

Cystoisospora

Answer

Cryptosporidium

Answer

Cyclospora

Answer

Cryptococcus

Parasitology — MCQs

Parasitology — MCQs

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