Parasitology Practice Questions

Q: Which of the following parasites is NOT transmitted via the feco-oral route?

Strongyloides stercoralis. ### Explanation The correct answer is **A. *Strongyloides stercoralis***. **1. Why *Strongyloides stercoralis* is the correct answer:** The primary mode of transmission for *Strongyloides stercoralis* is **skin penetration** (usually through bare feet) by filariform larvae present in contaminated soil. Unlike the other options, it does not enter the body via ingestion. It is also unique for its ability to cause **autoinfection**, where rhabditiform larvae transform into filariform larvae within the host's intestine and re-penetrate the perianal skin or intestinal mucosa. **2. Analysis of Incorrect Options:** * **B. *Taenia solium*:** Transmitted via the feco-oral route through the ingestion of food or water contaminated with eggs (leading to **Cysticercosis**). Note: Ingestion of undercooked pork containing cysticerci leads to intestinal Taeniasis. * **C. *Ascaris lumbricoides*:** Transmitted via the feco-oral route through the ingestion of **embryonated eggs** from contaminated soil or food. * **D. *Dracunculus medinensis*:** Transmitted via the feco-oral route by drinking water containing **Cyclops** (intermediate host) infected with L3 larvae. **3. NEET-PG Clinical Pearls:** * **Skin Penetrators (Mnemonic: "S-A-N-D"):** ***S***trongyloides, ***A***ncylostoma (Hookworm), ***N***ecator (Hookworm), and ***D***ermatobia. * **Strongyloides & Immunosuppression:** In patients on steroids or with HTLV-1, it can cause **Hyperinfection Syndrome**, leading to disseminated disease and Gram-negative sepsis. * **Diagnostic Choice:** The **Baermann technique** or agar plate culture is used to detect larvae in stool (eggs are rarely seen as they hatch in the intestinal mucosa). * **Treatment of Choice:** **Ivermectin** is the drug of choice for *Strongyloides*, whereas Albendazole is preferred for most other soil-transmitted helminths.

Q: Which statement is false regarding malaria?

Relapse is seen in P. falciparum infection. ### Explanation **1. Why Option C is the Correct (False) Statement:** Relapse occurs due to the activation of **hypnozoites** (dormant stages) in the liver. This phenomenon is strictly seen in **_Plasmodium vivax_** and **_Plasmodium ovale_**. _Plasmodium falciparum_ (and _P. malariae_) does not form hypnozoites; therefore, it does not cause relapse. Any reappearance of _P. falciparum_ in the blood after treatment is termed **recrudescence**, which results from the survival of erythrocytic forms in the blood due to inadequate treatment or drug resistance. **2. Analysis of Other Options:** * **Option A (True):** _P. falciparum_ is the most severe form because it can infect **RBCs of all ages** (young and old), leading to high parasitemia. In contrast, _P. vivax_ prefers reticulocytes (young RBCs), and _P. malariae_ prefers senescent (old) RBCs. * **Option B (True):** In _P. vivax_ infections, the infected RBCs become **enlarged and pale**. This is a key diagnostic feature under the microscope, often accompanied by the presence of **Schüffner’s dots**. * **Option D (True):** Malaria is transmitted by the bite of an infected **female Anopheles mosquito**, which requires a blood meal for egg production. **3. NEET-PG High-Yield Pearls:** * **Maurer’s dots:** Seen in _P. falciparum_ infected RBCs. * **Ziemann’s dots:** Seen in _P. malariae_ infected RBCs. * **Crescent-shaped gametocytes:** Pathognomonic for _P. falciparum_. * **Drug of Choice for Relapse:** **Primaquine** is administered for 14 days to eradicate hypnozoites (radical cure). It is contraindicated in G6PD deficiency. * **Most common cause of Nephrotic Syndrome (Quartan Malarial Nephropathy):** _P. malariae_.

Q: A pregnant woman in her 1st trimester is given spiramycin, but she does not complete the course. The baby is born with hydrocephalus and infection. Which organism is the most likely cause of this infection?

Toxoplasma gondii. ### Explanation **Correct Answer: C. Toxoplasma gondii** The clinical scenario describes a classic case of **Congenital Toxoplasmosis**. The definitive clue is the use of **Spiramycin**, which is the drug of choice for primary maternal Toxoplasma infection in the first trimester to prevent vertical transmission. **Why Toxoplasma gondii is correct:** Toxoplasmosis is caused by the parasite *Toxoplasma gondii*. If a mother acquires a primary infection during pregnancy, the parasite can cross the placenta. While the risk of transmission is lowest in the first trimester, the severity of fetal damage is highest. The "Classic Triad" of congenital toxoplasmosis includes: 1. **Hydrocephalus** (as seen in this case) 2. **Chorioretinitis** (most common finding) 3. **Intracranial calcifications** (typically diffuse/scattered) **Why other options are incorrect:** * **HSV:** Usually transmitted during delivery (birth canal). It typically presents with skin vesicles, keratoconjunctivitis, or encephalitis, rather than hydrocephalus at birth. * **Treponema pallidum (Syphilis):** Presents with features like snuffles, Hutchinson’s teeth, saddle nose, and periostitis. Treatment is Penicillin, not Spiramycin. * **CMV:** The most common congenital infection. While it causes microcephaly and **periventricular** calcifications, it is not treated with Spiramycin (Ganciclovir is used for symptomatic neonates). **NEET-PG High-Yield Pearls:** * **Drug of Choice:** Spiramycin is used for maternal infection (to prevent transmission). If fetal infection is confirmed (via amniotic fluid PCR), the treatment switches to **Pyrimethamine, Sulfadiazine, and Folinic acid**. * **Calcification Pattern:** Toxoplasmosis = Diffuse/Scattered; CMV = Periventricular. * **Triad of Sabin:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Transmission Risk:** Increases with gestational age (highest in 3rd trimester), but severity decreases.

Q: Which of the following parasites does not pass through the liver during its life cycle?

Fasciolopsis buski. ### Explanation The correct answer is **Fasciolopsis buski**. **1. Why Fasciolopsis buski is correct:** *Fasciolopsis buski* is the **Giant Intestinal Fluke**. Its life cycle is confined primarily to the gastrointestinal tract. After humans ingest metacercariae (encysted on aquatic plants like water caltrop or chestnuts), the larvae excyst in the duodenum and attach directly to the **intestinal mucosa**. They mature into adult flukes in the small intestine without any extra-intestinal migration. Therefore, they do not pass through or reside in the liver. **2. Why the other options are incorrect:** * **Fasciola hepatica (Sheep Liver Fluke):** After excysting in the duodenum, the larvae penetrate the intestinal wall, migrate across the peritoneal cavity, and **bore through the liver parenchyma** to reach the bile ducts, where they mature. * **Clonorchis sinensis (Chinese Liver Fluke) & Opisthorchis felineus (Cat Liver Fluke):** These are "biliary flukes." Upon ingestion, the larvae migrate from the duodenum through the **Ampulla of Vater** directly into the common bile duct and distal biliary capillaries of the liver to mature. **3. High-Yield Clinical Pearls for NEET-PG:** * **Habitat:** *F. buski* (Small Intestine) vs. *F. hepatica/Clonorchis* (Biliary tract). * **Intermediate Hosts:** All four flukes require **snails** as the 1st intermediate host. * **Infective Stage:** **Metacercariae** for all four. * **Diagnostic Stage:** Eggs in stool. Note that *F. buski* and *F. hepatica* eggs are operculated and morphologically identical (large, bile-stained). * **Complication:** *Clonorchis sinensis* is strongly associated with **Cholangiocarcinoma** (Biliary tract cancer).

Q: Which organism, associated with fish consumption, also causes carcinoma of the gallbladder?

Clonorchis sinensis. **Explanation:** **Clonorchis sinensis** (the Chinese Liver Fluke) is the correct answer. It is a trematode acquired by consuming undercooked or raw **freshwater fish** containing encysted metacercariae. Once ingested, the larvae migrate to the biliary tract. Chronic infection leads to mechanical irritation and the release of inflammatory cytokines, causing chronic biliary inflammation, hyperplasia, and fibrosis. This chronic state is a major risk factor for **Cholangiocarcinoma** (bile duct cancer) and is also strongly associated with **carcinoma of the gallbladder**. **Analysis of Incorrect Options:** * **Gnathostoma:** A nematode acquired from undercooked fish/poultry; it typically causes **larva migrans** (cutaneous or visceral), not biliary malignancy. * **Strongyloides cantonensis (Angiostrongylus):** Known as the rat lungworm, it is acquired from snails/slugs and is a leading cause of **eosinophilic meningitis**. * **Hymenolepis diminuta:** The rat tapeworm; it causes mild intestinal infection in humans via ingestion of infected insects (fleas/beetles) found in grain. It has no association with fish or biliary cancer. **High-Yield Clinical Pearls for NEET-PG:** * **IARC Classification:** *Clonorchis sinensis* and *Opisthorchis viverrini* are classified as Group 1 carcinogens. * **Intermediate Hosts:** 1st host = Snail; 2nd host = Freshwater fish (Cyprinidae family). * **Diagnosis:** Identification of characteristic "operculated eggs with a small knob (abopercular protuberance)" in stool or bile. * **Drug of Choice:** Praziquantel. * **Differential:** While *Clonorchis* causes biliary cancer, **Schistosoma haematobium** is associated with Squamous Cell Carcinoma of the **Urinary Bladder**.

Q: Which of the following is NOT typically seen in Plasmodium falciparum infection?

Relapses. **Explanation:** The correct answer is **Relapses**. In parasitology, a "relapse" specifically refers to the recurrence of symptoms due to the activation of dormant liver stages known as **hypnozoites**. 1. **Why Relapse is NOT seen in *P. falciparum*:** Relapses occur only in *Plasmodium vivax* and *Plasmodium ovale* infections because these species produce hypnozoites that can remain dormant in the liver for months or years. *P. falciparum* (and *P. malariae*) do not have a hypnozoite stage; therefore, once the parasite leaves the liver, no dormant forms remain to cause a true relapse. Any recurrence of *P. falciparum* after treatment is termed a **recrudescence**, which results from the survival of erythrocytic forms in the blood due to inadequate treatment or drug resistance. 2. **Analysis of Incorrect Options:** * **Cerebral Malaria:** This is the most common cause of death in *P. falciparum* infection, characterized by sequestration of parasitized RBCs in cerebral microvasculature. * **Hemoglobinuria:** Also known as **Blackwater Fever**, this is a severe complication of *P. falciparum* involving massive intravascular hemolysis and subsequent dark urine. * **Malignant Malaria:** *P. falciparum* is known as "Malignant Tertian Malaria" because of its high parasite load and potential for multi-organ failure. **High-Yield Clinical Pearls for NEET-PG:** * **Hypnozoites:** Only seen in *P. vivax* and *P. ovale*. Treatment requires **Primaquine** or **Tafenoquine** for radical cure. * **Maurer’s Clefts:** Seen in RBCs infected with *P. falciparum*. * **Multiple Rings & Accole Forms:** Characteristic peripheral smear findings for *P. falciparum*. * **Recrudescence:** Associated with *P. falciparum* and *P. malariae*.

Q: Hydatid sand is composed of what structures?

Protoscolex. **Explanation:** Hydatid disease is caused by the larval stage of the tapeworm *Echinococcus granulosus*. The hydatid cyst is a fluid-filled structure that develops primarily in the liver or lungs. **Why Option C is Correct:** **Hydatid sand** refers to the granular sediment found at the bottom of a mature hydatid cyst. It is primarily composed of **protoscolices** (the infectious larval heads), along with free brood capsules and calcareous corpuscles that have detached from the germinal layer. When the cyst is shaken or aspirated, these microscopic structures settle, resembling grains of sand. **Analysis of Incorrect Options:** * **A. Scolex:** This is the head of an adult tapeworm. While a protoscolex is a precursor to a scolex, the term "scolex" specifically refers to the attachment organ of the adult worm found in the definitive host (dog), not the sediment in the larval cyst. * **B. Cyst:** The cyst is the entire macroscopic pathological structure (containing the ectocyst, endocyst, and fluid). It is the container, not a component of the "sand" within it. * **D. Brood capsule:** While brood capsules (small secondary cysts attached to the germinal layer) can be part of the sediment if they rupture or detach, the diagnostic hallmark and primary constituent of hydatid sand are the **protoscolices**. **High-Yield NEET-PG Pearls:** * **Casoni Test:** An immediate hypersensitivity skin test used for diagnosis (now largely replaced by serology/ELISA). * **Water Lily Sign:** Seen on imaging when the endocyst ruptures and the membranes float in the pericyst. * **Treatment:** Surgical removal is preferred, but **PAIR** (Puncture, Aspiration, Injection of scolicidal agent like hypertonic saline, and Re-aspiration) is an alternative. * **Drug of Choice:** Albendazole. * **Risk:** Spillage of hydatid sand during surgery can lead to **anaphylactic shock** or secondary cyst formation.

Q: Man serves as the intermediate host for which of the following parasites?

Hydatid cyst. In parasitology, the classification of hosts depends on the stage of the parasite’s life cycle: the **Definitive Host** harbors the adult (sexual) stage, while the **Intermediate Host** harbors the larval (asexual) stage. **Why Hydatid Cyst is correct:** Hydatid disease is caused by the tapeworm *Echinococcus granulosus*. * **Definitive Host:** Dogs (and other canines), which harbor the adult worm in their intestines. * **Intermediate Host:** Sheep (natural) and **Humans (accidental)**. In humans, the ingested eggs hatch into oncospheres that migrate to organs (primarily the liver and lungs) to form **hydatid cysts**, which represent the larval stage. Since humans harbor the larvae, they serve as the intermediate host. **Why the other options are incorrect:** * **Filariasis (*Wuchereria bancrofti*):** Humans serve as the **Definitive Host** because the adult worms reside in the human lymphatic system. The mosquito (Culex) serves as the intermediate host, harboring the infective larval stages. * **Both:** This is incorrect because the host status for Filariasis and Hydatid disease is fundamentally different regarding the human role. **High-Yield Clinical Pearls for NEET-PG:** * **Dead-end Host:** Humans are "dead-end" intermediate hosts for *E. granulosus* because the cycle usually terminates there (dogs do not typically eat infected human viscera). * **Other parasites where Man is the Intermediate Host:** *Plasmodium* (Malaria), *Toxoplasma gondii*, and *Taenia solium* (in the case of Cysticercosis). * **Diagnosis:** Casoni’s test (historical) and "Water lily sign" on ultrasound/MRI are classic associations for Hydatid cysts.

Q: Chagas disease is caused by which of the following organisms?

Trypanosoma. **Explanation:** **Chagas disease** (American Trypanosomiasis) is caused by the protozoan parasite **Trypanosoma cruzi**. It is primarily transmitted to humans through the feces of the **Triatomine bug** (also known as the "kissing bug" or "reduviid bug"). The parasite enters the body through the bite wound or mucosal surfaces. * **Why Option A is correct:** *Trypanosoma cruzi* is the specific etiological agent. In the acute phase, it is characterized by **Romaña’s sign** (unilateral painless periorbital edema). In the chronic phase, it leads to visceral involvement, most notably **Dilated Cardiomyopathy**, **Megaesophagus**, and **Megacolon** due to the destruction of autonomic nerve plexuses. * **Why other options are incorrect:** * **Brucella:** A gram-negative coccobacillus causing Brucellosis (undulant fever), typically transmitted via unpasteurized dairy. * **Trichinella:** A nematode (*Trichinella spiralis*) causing Trichinellosis, usually acquired by consuming undercooked pork containing encysted larvae in muscle. * **Bartonella:** *Bartonella henselae* causes Cat-scratch disease, while *Bartonella quintana* causes Trench fever. **High-Yield Clinical Pearls for NEET-PG:** 1. **Vector:** Reduviid bug (Triatoma). 2. **Infective Stage:** Metacyclic trypomastigotes (found in bug feces). 3. **Diagnostic feature:** C-shaped trypomastigotes in peripheral blood smears during the acute phase; Amastigotes in tissue (pseudocysts). 4. **Drug of Choice:** Benznidazole or Nifurtimox. 5. **Gold Standard for Chronic phase:** Serology (ELISA/IFA).

Question 1

Which of the following parasites is NOT transmitted via the feco-oral route?

Accepted Answer

Strongyloides stercoralis

Answer

Tenia solium

Answer

Ascaris

Answer

Dracunculosis

Question 2

Which statement is false regarding malaria?

Accepted Answer

Relapse is seen in P. falciparum infection

Answer

P. falciparum infects all forms of RBC

Answer

RBC size is increased in P. vivax infection

Answer

The female mosquito transmits the disease

Question 3

A 30-year-old veterinarian presents for a first-trimester prenatal check-up with no complaints. Routine physical examination is significant only for mild cervical lymphadenopathy. She was prescribed spiramycin but was noncompliant. Her baby is born with hydrocephalus and cerebral calcifications. Which of the following organisms is most likely responsible?

Accepted Answer

Toxoplasma gondii

Answer

Isospora belli

Answer

Leishmania donovani

Answer

Plasmodium vivax

Question 4

A pregnant woman in her 1st trimester is given spiramycin, but she does not complete the course. The baby is born with hydrocephalus and infection. Which organism is the most likely cause of this infection?

Accepted Answer

Toxoplasma gondii

Answer

Herpes Simplex Virus (HSV)

Answer

Treponema pallidum

Answer

Cytomegalovirus (CMV)

Question 5

Which of the following parasites does not pass through the liver during its life cycle?

Accepted Answer

Fasciolopsis buski

Answer

Fasciola hepatica

Answer

Clonorchis sinensis

Answer

Opisthorchis felineus

Question 6

Which organism, associated with fish consumption, also causes carcinoma of the gallbladder?

Accepted Answer

Clonorchis sinensis

Answer

Gnathostoma

Answer

Strongyloides cantonensis

Answer

Hymenolepis diminuta

Question 7

Which of the following is NOT typically seen in Plasmodium falciparum infection?

Accepted Answer

Relapses

Answer

Hemoglobinuria

Answer

Cerebral malaria

Answer

Malignant malaria

Question 8

Hydatid sand is composed of what structures?

Accepted Answer

Protoscolex

Answer

Scolex

Answer

Cyst

Answer

Brood capsule

Question 9

Man serves as the intermediate host for which of the following parasites?

Accepted Answer

Hydatid cyst

Answer

Filariasis

Answer

Both

Answer

None

Question 10

Chagas disease is caused by which of the following organisms?

Accepted Answer

Trypanosoma

Answer

Brucella

Answer

Trichenella

Answer

Bartonella

Parasitology — MCQs

Parasitology — MCQs

On this page

Practice by Chapter

Want unlimited practice?