Parasitology Practice Questions

Q: Hookworm thrives on what component of blood?

Plasma. ### Explanation The correct answer is **Plasma**. **Underlying Medical Concept:** Hookworms (*Ancylostoma duodenale* and *Necator americanus*) are hematophagous nematodes that attach to the mucosal villi of the small intestine using their buccal capsules. While it is a common misconception that they consume whole blood for nutrition, they primarily ingest blood to extract **plasma proteins and glucose**. The hookworm’s digestive tract is inefficient at processing solid cellular components. Once the worm draws blood, it rapidly passes the red blood cells (RBCs) through its intestine relatively intact and unutilized. The worm primarily utilizes the liquid portion—**plasma**—as its main source of nourishment. The iron deficiency anemia associated with hookworm infestation is actually a result of the **accidental loss of RBCs** (hemorrhage) caused by the worm's anticoagulant (ancylostomin) and its inability to digest the iron-rich hemoglobin it ingests. **Analysis of Incorrect Options:** * **A. Whole blood:** Although the worm ingests whole blood, it does not "thrive" on it entirely; it selectively utilizes plasma components and discards the rest. * **C. Serum:** Serum is plasma minus clotting factors. Since the worm ingests circulating blood (which contains fibrinogen), it is consuming plasma, not serum. * **D. Red blood cells:** Hookworms cannot effectively digest the hemoglobin within RBCs. The RBCs are excreted in the host's feces, leading to the characteristic occult blood loss. **NEET-PG High-Yield Pearls:** * **Daily blood loss:** *A. duodenale* (0.15–0.2 ml/day) causes more blood loss than *N. americanus* (0.03 ml/day). * **Clinical Presentation:** Microcytic hypochromic anemia (Iron deficiency) and Ground itch (at the site of larval entry). * **Infective Stage:** Filariform larva (L3). * **Diagnostic Feature:** Non-bile stained, segmented eggs with a clear space between the shell and the embryo.

Q: Apart from Plasmodium, which of the following can infect red blood cells in ring forms?

Babesia microti. **Explanation:** The correct answer is **Babesia microti**. This is a high-yield concept in parasitology because *Babesia* is the primary differential diagnosis for *Plasmodium falciparum* on a peripheral blood smear. **1. Why Babesia microti is correct:** *Babesia* is an intraerythrocytic protozoan. Like *Plasmodium*, it infects red blood cells (RBCs) and presents as small, pleomorphic **ring forms** (trophozoites). * **Key Diagnostic Feature:** Unlike Malaria, *Babesia* does not produce pigment (hemozoin) or have a gametocyte stage. It classically forms a **"Maltese Cross"** appearance (tetrads) during asexual reproduction (budding), which is pathognomonic. **2. Why other options are incorrect:** * **Trypanosoma:** These are extracellular hemoflagellates found in the **plasma**, not inside the RBCs. They appear as C-shaped or U-shaped organisms with a flagellum and undulating membrane. * **Schistosoma:** These are trematodes (flukes). The adult worms reside in the **venous plexus** (mesenteric or vesical), and their eggs are found in stool or urine. They do not infect RBCs. * **Microfilaria:** These are the larval stages of nematodes (like *Wuchereria bancrofti*). They are found in the **lymphatics or blood plasma**, appearing as large, multi-nucleated worm-like structures, never as intraerythrocytic rings. **NEET-PG High-Yield Pearls:** * **Vector:** *Babesia* is transmitted by the **Ixodes tick** (the same vector for Lyme disease). * **Clinical Presentation:** Often causes a malaria-like illness (fever, hemolytic anemia). It is particularly severe or fatal in **asplenic patients**. * **Morphology:** Look for "Maltese Cross" and the absence of Schüffner’s dots or malarial pigment.

Q: Night blood survey is done in which of the following conditions?

Filaria. **Explanation:** The correct answer is **Filaria (Option A)**. This is because the most common causative agent of lymphatic filariasis, *Wuchereria bancrofti*, exhibits a unique biological phenomenon known as **Nocturnal Periodicity**. 1. **Why Filaria is correct:** The microfilariae (larval forms) of *W. bancrofti* and *Brugia malayi* circulate in the peripheral blood primarily at night (usually between **10 PM and 2 AM**). During the day, they sequester in the deep capillaries of the lungs. This timing coincides with the peak biting activity of the vector, the *Culex* mosquito. Therefore, a "Night Blood Survey" is essential to achieve maximum sensitivity for diagnosis via peripheral smear. 2. **Why other options are incorrect:** * **Typhoid (B):** Diagnosis is based on the **BASU** rule (Blood culture in 1st week, Antibody/Widal in 2nd, Stool in 3rd, Urine in 4th). There is no diurnal variation in bacteremia. * **Malaria (C):** While malarial paroxysms have cycles, the parasites are generally present in the blood throughout the day. Thick and thin smears are best taken during or immediately after a febrile peak, regardless of the clock time. * **Kala-azar (D):** Caused by *Leishmania donovani*, this is diagnosed via bone marrow or splenic aspiration to find LD bodies; the parasite does not show nocturnal peripheral periodicity. **High-Yield Clinical Pearls for NEET-PG:** * **DEC Provocative Test:** If a night survey is not possible, a small dose of Diethylcarbamazine (2mg/kg) can be given; it brings microfilariae into the peripheral blood within 30–60 minutes even during the day. * **Exceptions:** *Loa loa* (African eye worm) exhibits **Diurnal periodicity** (daytime), while *W. bancrofti* var. *pacifica* is **non-periodic**. * **Stain of choice:** Giemsa or Leishman stain is used to visualize the sheath and nuclei of microfilariae.

Q: Which of the following infections resembles malignancy?

Echinococcus multilocularis. **Explanation:** The correct answer is **Echinococcus multilocularis**. This parasite causes **Alveolar Echinococcosis (AE)**, a condition notorious for its "malignant" clinical behavior. **Why Echinococcus multilocularis is correct:** Unlike *E. granulosus*, which forms a single, well-circumscribed fluid-filled cyst with a protective laminated membrane, *E. multilocularis* lacks a proper limiting membrane. This allows the larval tissue to grow by **external budding**, resulting in a multi-loculated, honeycombed mass of small vesicles. This mass **infiltrates** the surrounding liver parenchyma and can **metastasize** to distant organs (lungs or brain) via hematogenous or lymphatic spread, mimicking a metastatic carcinoma or primary hepatocellular carcinoma. **Why the other options are incorrect:** * **Echinococcus granulosus:** Causes **Cystic Echinococcosis**. It forms slow-growing, unilocular cysts that expand by internal pressure but do not infiltrate tissue or metastasize. * **Echinococcus vogeli & E. oligarthrus:** These cause **Polycystic Echinococcosis**. While they form multiple cysts, they are rare and do not exhibit the aggressive, invasive, and metastatic "malignant" behavior characteristic of *E. multilocularis*. **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Foxes (most common for *E. multilocularis*); Dogs (for *E. granulosus*). * **Intermediate Host:** Rodents (for *E. multilocularis*); Sheep (for *E. granulosus*). * **Imaging:** *E. multilocularis* often shows irregular masses with central necrosis and "scattered calcifications," often mistaken for a tumor on CT scans. * **Treatment:** Unlike cystic disease, alveolar echinococcosis often requires radical surgical resection (similar to a tumor) and long-term Albendazole therapy.

Q: Which of the following helminths primarily produces gastrointestinal symptoms, without lung involvement, during the course of its infection?

Trichuris trichiura. ### Explanation The correct answer is **Trichuris trichiura (Whipworm)**. **1. Why Trichuris trichiura is correct:** The key concept here is the **Loeffler’s cycle** (lung migration). Unlike many other intestinal nematodes, *Trichuris trichiura* follows a **direct life cycle** without a heart-lung migration phase. After ingestion of embryonated eggs, the larvae hatch in the small intestine, move to the cecum, and mature into adults. Since the larvae never enter the bloodstream or the alveoli, there are **no pulmonary symptoms** (like cough or wheezing). Clinical manifestations are strictly gastrointestinal, ranging from abdominal pain to **rectal prolapse** in heavy infections. **2. Why the other options are incorrect:** * **Ascaris lumbricoides & Strongyloides stercoralis:** Both undergo a mandatory heart-lung migration phase. Larvae penetrate the alveolar walls, causing **Loeffler’s syndrome** (eosinophilic pneumonia, cough, and dyspnea) before being swallowed back into the GI tract. * **Dirofilaria immitis:** Known as the "dog heartworm," it primarily affects the pulmonary arteries and heart. In humans (accidental hosts), it often presents as a **"coin lesion"** on a chest X-ray due to pulmonary infarction, making it a primarily respiratory/vascular concern rather than a GI one. **3. NEET-PG High-Yield Pearls:** * **Mnemonics for Lung Migration:** Remember **"NASSA"** (Necator americanus, Ascaris lumbricoides, Strongyloides stercoralis, Schistosomes, Ancylostoma duodenale). * **Trichuris trichiura:** Look for "Whip-like" morphology, **"Barrel-shaped eggs with bipolar mucus plugs,"** and the classic association with **rectal prolapse** in children. * **Strongyloides:** Unique because it can cause **autoinfection** and hyperinfection syndrome in immunocompromised patients.

Q: The provided diagram shows a blood smear. Which species of Plasmodium is depicted?

Plasmodium falciparum. ***Plasmodium falciparum*** - Characterized by **multiple ring forms** within a single red blood cell and **accolé/appliqué forms** (rings positioned at the periphery of the RBC). - **Normal-sized RBCs** with **no Schüffner's dots**, and distinctive **crescent/banana-shaped gametocytes** when present. *Plasmodium vivax* - Shows **enlarged RBCs** with prominent **Schüffner's dots** (fine stippling throughout the cytoplasm). - Typically displays **single ring forms** per RBC and **amoeboid trophozoites** with irregular shapes. *Plasmodium ovale* - Features **oval-shaped, enlarged RBCs** with **Schüffner's dots** similar to P. vivax. - Shows **single ring forms** and **compact trophozoites**, but RBCs often have a characteristic **fimbriated edge**. *Plasmodium malariae* - Presents with **normal-sized RBCs** and **thick, band-form trophozoites** that span across the RBC. - Shows **single ring forms** and characteristic **rosette-pattern schizonts** with 6-12 merozoites arranged around central pigment.

Q: Which of the following acts as a reservoir for Toxoplasma gondii?

Toxoplasma gondii. **Explanation:** The question identifies **Toxoplasma gondii** as its own reservoir, which refers to the biological cycle where the parasite persists in various hosts. *Toxoplasma gondii* is an obligate intracellular protozoan. Its definitive hosts are members of the **Felidae family (cats)**, where sexual reproduction occurs. However, it has a remarkably broad host range, using virtually any warm-blooded animal (including humans, rodents, and livestock) as intermediate hosts where it maintains a chronic presence in the form of tissue cysts. **Analysis of Options:** * **Toxoplasma gondii (Correct):** In the context of this question, the organism itself represents the infection cycle. The reservoir system involves the feline-environment-prey cycle. * **Rabies (Incorrect):** Rabies is a viral zoonosis. Its primary reservoirs are wild animals such as bats, raccoons, skunks, and foxes (and domestic dogs in developing regions). * **Streptocerca infection (Incorrect):** Caused by *Mansonella streptocerca*, this filarial nematode is transmitted by *Culicoides* biting midges. The primary reservoir is humans (and occasionally monkeys). * **Plague (Incorrect):** Caused by *Yersinia pestis*, the primary reservoirs are wild rodents (e.g., rats, ground squirrels). **High-Yield Clinical Pearls for NEET-PG:** * **Transmission:** Ingestion of oocysts (cat feces), bradyzoites (undercooked meat), or transplacental transfer. * **Congenital Toxoplasmosis Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Diagnosis:** Sabin-Feldman Dye Test (Gold Standard), though rarely used now; IgM/IgG ELISA is standard. * **Drug of Choice:** Pyrimethamine + Sulfadiazine. * **AIDS Patients:** Most common cause of CNS mass lesions (Ring-enhancing lesions on CT/MRI).

Q: A 35-year-old man who recently traveled to a tropical country develops chronic, severe dysentery. Colonoscopy demonstrates ulceration of the cecum, and a cecal biopsy reveals 15-to-40 micron amoebae with ingested erythrocytes and small nuclei with distinctive tiny central karyosomes. Which of the following organisms is the most likely culprit?

Entamoeba histolytica. ### Explanation **1. Why Entamoeba histolytica is Correct:** The clinical presentation of chronic dysentery combined with specific histopathological findings is pathognomonic for *Entamoeba histolytica*. * **Ingested Erythrocytes (Erythrophagocytosis):** This is the most definitive diagnostic feature used to distinguish the pathogenic *E. histolytica* from the morphologically identical but non-pathogenic *E. dispar*. * **Nuclear Morphology:** The description of a small, central karyosome (nucleolus) and fine, peripheral chromatin is characteristic of the *Entamoeba* genus. * **Pathology:** *E. histolytica* typically causes "flask-shaped" ulcers in the cecum and colon by secreting proteolytic enzymes (histolysins) that invade the submucosa. **2. Why the Other Options are Incorrect:** * **Acanthamoeba sp:** Primarily causes Granulomatous Amoebic Encephalitis (GAE) or keratitis (associated with contact lens use). It does not cause dysentery. * **Balantidium coli:** While it causes similar large-bowel ulceration and dysentery, it is a much larger ciliated protozoan (50–200 µm) with a characteristic kidney-shaped macronucleus. It does not ingest RBCs. * **Giardia lamblia:** This parasite affects the duodenum and jejunum (small intestine), leading to malabsorption and foul-smelling, fatty stools (steatorrhea), not bloody dysentery or colonic ulcers. **3. NEET-PG High-Yield Pearls:** * **Trophozoite vs. Cyst:** The trophozoite is the invasive form (found in dysenteric stools); the quadrinucleated cyst is the infective form (found in chronic cases/carriers). * **Commonest Site:** The cecum and ascending colon are the most common sites for intestinal amoebiasis. * **Extra-intestinal Complication:** The most common is an **Amoebic Liver Abscess**, typically presenting with "anchovy sauce" pus. * **Treatment:** Metronidazole or Tinidazole (luminal agents like Paromomycin are added to eradicate cysts).

Q: What is the shortest incubation period in malaria?

Plasmodium falciparum. ### Explanation The **incubation period** in malaria refers to the time interval between the bite of an infected female *Anopheles* mosquito and the onset of clinical symptoms (usually fever). This period is primarily determined by the duration of the **pre-erythrocytic (exo-erythrocytic) schizogony** in the liver. **Why Plasmodium falciparum is correct:** *Plasmodium falciparum* has the shortest pre-erythrocytic cycle, lasting approximately **5–7 days**, leading to an average incubation period of **9–14 days** (range can be as short as 7 days). Because it lacks a dormant hypnozoite stage and replicates rapidly, it manifests clinically faster than other species. **Analysis of Incorrect Options:** * **P. vivax:** The incubation period is typically **12–17 days**. While the liver stage lasts about 8 days, the onset of symptoms is slightly slower than *P. falciparum*. It can also cause relapses due to dormant **hypnozoites**. * **P. ovale:** Similar to *P. vivax*, it has an incubation period of **16–18 days** and possesses a hypnozoite stage. * **P. malariae:** This species has the **longest** incubation period, typically ranging from **18–40 days**. Its pre-erythrocytic stage lasts about 15 days, and it has a slower erythrocytic cycle (72 hours). **NEET-PG High-Yield Pearls:** 1. **Shortest Incubation Period:** *P. falciparum* (9–14 days). 2. **Longest Incubation Period:** *P. malariae* (18–40 days). 3. **Pre-erythrocytic Cycle Duration:** *P. falciparum* (6 days) < *P. vivax* (8 days) < *P. ovale* (9 days) < *P. malariae* (15 days). 4. **Relapse vs. Recrudescence:** Relapse (liver stage) occurs in *P. vivax* and *P. ovale*. Recrudescence (blood stage survival) is characteristic of *P. falciparum* and *P. malariae*.

Q: A 26-year-old lady complains of discomfort during intercourse. Pelvic examination demonstrates a frothy, yellow-green vaginal discharge with a strong odour and small, red, ulcerations of the vaginal wall. A wet mount preparation demonstrates motile, flagellated protozoa. Which of the following is the most likely causative organism?

Trichomonas vaginalis. ### Explanation The clinical presentation described is a classic case of **Trichomoniasis**, caused by the flagellated protozoan **_Trichomonas vaginalis_**. **Why Option B is Correct:** * **Clinical Features:** The "frothy, yellow-green discharge" and "foul odor" are hallmark signs. * **Strawberry Cervix:** The "small, red ulcerations" on the vaginal wall and cervix (punctate hemorrhages) are known as **colpitis macularis** or "strawberry cervix," which is highly specific for Trichomoniasis. * **Diagnosis:** A wet mount microscopy showing **motile, flagellated organisms** (pear-shaped) is the definitive bedside diagnostic feature. **Why the Other Options are Incorrect:** * **A & D (Giardia & Entamoeba):** These are intestinal protozoa. While they can cause diarrhea or liver abscesses, they are not standard causes of vaginitis or the specific clinical findings mentioned. * **C (Candida albicans):** Candidiasis typically presents with a thick, white, "curd-like" or "cottage cheese" discharge, intense pruritus, and a normal vaginal pH ( 4.5). * **Treatment:** The drug of choice is **Metronidazole** (2g single dose or 500mg BD for 7 days). * **Partner Management:** It is a Sexually Transmitted Infection (STI); therefore, **simultaneous treatment of the partner** is mandatory to prevent reinfection. * **Whiff Test:** May be positive (amine odor) in Trichomoniasis, though more characteristic of Bacterial Vaginosis.

Question 1

Hookworm thrives on what component of blood?

Accepted Answer

Plasma

Answer

Whole blood

Answer

Serum

Answer

Red blood cells

Question 2

Apart from Plasmodium, which of the following can infect red blood cells in ring forms?

Accepted Answer

Babesia microti

Answer

Trypanosoma

Answer

Schistosoma

Answer

Microfilaria

Question 3

Night blood survey is done in which of the following conditions?

Accepted Answer

Filaria

Answer

Typhoid

Answer

Malaria

Answer

Kala-azar

Question 4

Which of the following infections resembles malignancy?

Accepted Answer

Echinococcus multilocularis

Answer

Echinococcus granulosus

Answer

Echinococcus vogeli

Answer

Echinococcus oligahus

Question 5

Which of the following helminths primarily produces gastrointestinal symptoms, without lung involvement, during the course of its infection?

Accepted Answer

Trichuris trichiura

Answer

Dirofilaria immitis

Answer

Strongyloides stercoralis

Answer

Ascaris lumbricoides

Question 6

The provided diagram shows a blood smear. Which species of Plasmodium is depicted?

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium vivax

Answer

Plasmodium ovale

Answer

Plasmodium malariae

Question 7

Which of the following acts as a reservoir for Toxoplasma gondii?

Accepted Answer

Toxoplasma gondii

Answer

Rabies

Answer

Streptocerca infection

Answer

Plague

Question 8

A 35-year-old man who recently traveled to a tropical country develops chronic, severe dysentery. Colonoscopy demonstrates ulceration of the cecum, and a cecal biopsy reveals 15-to-40 micron amoebae with ingested erythrocytes and small nuclei with distinctive tiny central karyosomes. Which of the following organisms is the most likely culprit?

Accepted Answer

Entamoeba histolytica

Answer

Acanthamoeba sp

Answer

Balantidium coli

Answer

Giardia lamblia

Question 9

What is the shortest incubation period in malaria?

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium vivax

Answer

Plasmodium malariae

Answer

Plasmodium ovale

Question 10

A 26-year-old lady complains of discomfort during intercourse. Pelvic examination demonstrates a frothy, yellow-green vaginal discharge with a strong odour and small, red, ulcerations of the vaginal wall. A wet mount preparation demonstrates motile, flagellated protozoa. Which of the following is the most likely causative organism?

Accepted Answer

Trichomonas vaginalis

Answer

Giardia lamblia

Answer

Candida albicans

Answer

Entamoeba histolytica

Parasitology — MCQs

Parasitology — MCQs

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