Parasitology Practice Questions

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.

Q: Which parasite commonly causes lung infestation?

Paragonimus westermanii. **Explanation:** **Paragonimus westermani** (the Oriental Lung Fluke) is the correct answer because it is the primary trematode specifically adapted to inhabit the lung parenchyma. Humans acquire the infection by consuming raw or undercooked crustaceans (crabs/crayfish) containing metacercariae. Once ingested, the larvae penetrate the intestinal wall, migrate through the diaphragm, and mature into adult worms within fibrous cysts in the lungs. This leads to **endemic hemoptysis**, often mimicking pulmonary tuberculosis. **Analysis of Incorrect Options:** * **Hymenolepis nana (Dwarf Tapeworm):** This is the most common intestinal helminth. Its entire life cycle occurs within the gastrointestinal tract; it does not have a migratory lung phase. * **Taenia saginata (Beef Tapeworm):** This parasite resides in the small intestine of humans. While the larvae (Cysticercus bovis) are found in the muscles of cattle, they do not typically cause lung infestation in humans. * **Echinococcus granulosus:** While this parasite can cause **Hydatid cysts** in the lungs (the second most common site after the liver), it is not primarily a "lung fluke." *Paragonimus* is the more "common" and definitive answer when discussing primary lung infestation in a parasitology context. **NEET-PG High-Yield Pearls:** * **Intermediate Hosts:** 1st: Snail (*Semisulcospira*); 2nd: Crustaceans (Crab/Crayfish). * **Diagnosis:** Identification of golden-brown, operculated eggs in **sputum** or feces. * **Radiology:** May show "ring-shadow" opacities or "cotton-wool" appearances. * **Drug of Choice:** Praziquantel.

Q: Which of the following parasites can be found in ocular muscles?

Trichinella. **Explanation:** The correct answer is **Trichinella spiralis**. This nematode is the causative agent of **Trichinellosis**, a disease typically acquired by consuming undercooked meat (especially pork) containing encysted larvae. **Why Trichinella is correct:** After ingestion, larvae mature in the small intestine, and the female releases newborn larvae into the bloodstream. These larvae have a high tropism for **striated muscles** with high metabolic activity and rich blood supply. The **extraocular muscles** are among the most frequently involved sites, followed by the diaphragm, tongue, and intercostal muscles. The larvae encyst within these muscles, leading to the classic clinical triad of **periorbital edema, myalgia, and eosinophilia.** **Why the other options are incorrect:** * **Ascaris lumbricoides:** This is an intestinal nematode. While its larvae undergo a heart-lung migration (Loeffler’s syndrome), they do not encyst in skeletal or ocular muscles. * **Enterobius vermicularis (Pinworm):** This parasite resides in the cecum and appendix. Its primary clinical manifestation is perianal pruritus; it does not involve muscle tissue. **NEET-PG High-Yield Pearls:** * **Diagnostic Feature:** Muscle biopsy showing **encysted larvae** (coiled larvae) is the gold standard. * **Laboratory Finding:** Marked **Eosinophilia** and elevated **Creatine Kinase (CK)** levels due to muscle destruction. * **Drug of Choice:** Albendazole or Mebendazole (effective against adult worms; steroids are added for severe systemic symptoms caused by larval encystment). * **Splinter hemorrhages:** Often seen under the fingernails in Trichinellosis, mimicking infective endocarditis.

Q: Which disease is transmitted by sandflies?

All of the above. **Explanation:** The correct answer is **D. All of the above**. This question tests your knowledge of the medical importance of the **Sandfly** (*Phlebotomus* species), which serves as a biological vector for several distinct bacterial and protozoal diseases. 1. **Kala-azar (Visceral Leishmaniasis):** Caused by *Leishmania donovani*, this is the most significant disease transmitted by the sandfly. The parasite is transmitted to humans through the bite of an infected female *Phlebotomus argentipes*. 2. **Oriental Sore (Cutaneous Leishmaniasis):** Caused by *Leishmania tropica* and *Leishmania major*, this condition presents as self-limiting skin ulcers and is also transmitted via the sandfly bite. 3. **Oroya Fever (Bartonellosis):** This is the acute febrile stage of infection by the bacterium *Bartonella bacilliformis*. It is transmitted by the sandfly *Phlebotomus verrucarum* (primarily found in the Andes region of South America). **High-Yield Clinical Pearls for NEET-PG:** * **Vector Characteristics:** Sandflies are small, hairy flies that are "hop-fliers" and active at night. Only the **females** bite as they require a blood meal for egg production. * **Sandfly Fever (Pappataci Fever):** In addition to the options above, sandflies also transmit this viral disease caused by a Phlebovirus. * **Infective Stage:** For Leishmaniasis, the infective stage for humans is the **promastigote**, while the diagnostic stage in human tissue is the **amastigote** (LD bodies). * **Control:** Unlike mosquitoes, sandflies are highly sensitive to DDT, making indoor residual spraying an effective control measure.

Question 1

Which of the following infections resembles malignancy?

Accepted Answer

Echinococcus multilocularis

Answer

Echinococcus granulosus

Answer

Echinococcus vogeli

Answer

Echinococcus oligahus

Question 2

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 3

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 4

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

Accepted Answer

Toxoplasma gondii

Answer

Rabies

Answer

Streptocerca infection

Answer

Plague

Question 5

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 6

What is the shortest incubation period in malaria?

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium vivax

Answer

Plasmodium malariae

Answer

Plasmodium ovale

Question 7

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

Question 8

Which parasite commonly causes lung infestation?

Accepted Answer

Paragonimus westermanii

Answer

Hymenolepis nana

Answer

Taenia saginata

Answer

Echinococcus granulosus

Question 9

Which of the following parasites can be found in ocular muscles?

Accepted Answer

Trichinella

Answer

Ascaris

Answer

Enterobius

Answer

None of the above

Question 10

Which disease is transmitted by sandflies?

Accepted Answer

All of the above

Answer

Oraya fever

Answer

Oriental sore

Answer

Kala-azar

Parasitology — MCQs

Parasitology — MCQs

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