Parasitology Practice Questions

Q: In which host does the flagellar stage of the Leishmania parasite occur?

Sandfly. ### Explanation The life cycle of *Leishmania* involves two distinct morphological stages: the **Amastigote** and the **Promastigote**. **Why the Sandfly is correct:** The **flagellar stage**, known as the **Promastigote**, occurs exclusively within the female **Sandfly** (*Phlebotomus* species). When the sandfly ingests a blood meal containing amastigotes, the parasites transform into elongated, motile promastigotes (15–25 µm) in the midgut. These possess a single anterior flagellum used for attachment and migration to the proboscis, from where they are transmitted to a new host. **Why the other options are incorrect:** * **A, B, and C (Man, Dog, Hamster):** These are all **vertebrate hosts** (Man is the definitive host; dogs and hamsters often serve as reservoirs). In vertebrate hosts, the parasite exists only in the **Amastigote** (LD body) stage. This stage is oval, non-motile, and **aflagellar** (lacks a visible external flagellum). It lives obligately within the phagolysosomes of macrophages. --- ### NEET-PG High-Yield Pearls: * **Infective Form:** Promastigote (injected by sandfly). * **Diagnostic Form:** Amastigote (seen in bone marrow or splenic aspirates, often described as having a nucleus and a rod-shaped kinetoplast). * **Culture Media:** *Leishmania* grows as promastigotes in **NNN (Novy-MacNeal-Nicolle) medium**. * **Vector:** *Phlebotomus argentipes* is the primary vector for Kala-azar in India. * **Gold Standard Diagnosis:** Splenic aspiration (highest sensitivity) but Bone Marrow aspiration is safer and more commonly performed.

Q: Chandler's Index is used for assessing the intensity of infection with which parasite?

Ancylostoma. **Explanation:** **Chandler’s Index** is a specialized epidemiological tool used to measure the intensity of infection in a community specifically for **Hookworms** (*Ancylostoma duodenale* and *Necator americanus*). It is calculated by determining the average number of eggs per gram (EPG) of feces in a sampled population. * **Why Ancylostoma is correct:** Hookworm disease severity is directly proportional to the "worm burden." Since adult hookworms cause chronic blood loss leading to Iron Deficiency Anemia, Chandler’s Index helps public health officials categorize the severity of the infection in a region (e.g., an index below 20000 is considered low, while above 25000 indicates a significant public health problem). **Analysis of Incorrect Options:** * **Filariasis:** Assessed using the **Microfilarial Rate** or **Density** (number of microfilariae per unit of blood) and the **Mosquito Infection Rate**. * **Ascariasis:** While egg counts are performed, there is no specific eponymous "index" like Chandler’s used for community assessment; it is usually measured by simple prevalence rates. * **Guinea worm (*Dracunculus medinensis*):** Monitored via case surveillance and the "certification of elimination" criteria, as it does not involve fecal egg counts. **High-Yield Clinical Pearls for NEET-PG:** * **Hookworm:** The most common cause of **Iron Deficiency Anemia** in the tropics. * **Egg Count Methods:** Kato-Katz technique is the gold standard for determining EPG for Chandler's Index. * **Other Indices to remember:** * **Breteau Index / House Index:** Used for *Aedes aegypti* (Dengue). * **Spleen Index:** Used for Malaria endemicity. * **Beaver’s Method:** Another method for calculating egg counts to estimate worm burden.

Q: If parasites are grown in culture with an unknown bacterial associate, what is it called?

Xenic culture. In parasitology, the classification of culture systems is based on the number and type of associated microbial species present in the medium. **Explanation of the Correct Answer:** **D. Xenic culture:** This term refers to a culture where the parasite is grown in the presence of an **unknown or unidentified** population of microorganisms (usually bacteria). This is common in the initial isolation of intestinal protozoa like *Entamoeba histolytica*, where the parasite requires the metabolic by-products of the patient's own fecal flora to survive. **Analysis of Incorrect Options:** * **A. Axenic culture:** This is a **pure culture** where the parasite grows in the absence of any other living metabolic organism. It is the "gold standard" for biochemical and immunological studies (e.g., Diamond’s medium for *E. histolytica*). * **B. Monoxenic culture:** The parasite is grown in association with **one single known** species of microorganism. For example, growing *Acanthamoeba* on a non-nutrient agar plate seeded with a known strain of *E. coli*. * **C. Polyxenic culture:** The parasite is grown with **multiple known** species of associated microorganisms. While similar to xenic, the key distinction is that in polyxenic cultures, the associates are identified. **High-Yield Clinical Pearls for NEET-PG:** * **Entamoeba histolytica:** Most commonly cultured using **NIH polyxenic medium** or **Diamond’s axenic medium**. Axenization is difficult and usually requires several subcultures. * **Leishmania & Trypanosoma:** Typically grown in **NNN (Novy-MacNeal-Nicolle) medium**, which is a diphasic medium. * **Acanthamoeba:** Cultured on **Non-nutrient agar (NNA)** using a "bacterial lawn" (monoxenic). * **Key Concept:** Xenic cultures are generally used for primary isolation, while axenic cultures are used for vaccine research and drug sensitivity testing.

Q: Sleeping sickness is caused by which of the following vectors?

Reduvid bug. **Explanation:** The question refers to **American Sleeping Sickness**, also known as **Chagas Disease**, which is caused by the protozoan parasite *Trypanosoma cruzi*. 1. **Why the Correct Answer is Right:** The **Reduviid bug** (also known as the Triatomine or "kissing bug") is the definitive vector for *T. cruzi*. The parasite is transmitted not through the bite itself, but via **posterior station inoculation**. The bug defecates while feeding; the infective metacyclic trypomastigotes present in the feces enter the human body when the host scratches the bite wound or rubs the feces into mucosal membranes (like the conjunctiva). 2. **Why the Other Options are Incorrect:** * **House fly (*Musca domestica*):** Acts primarily as a mechanical vector for enteric pathogens (e.g., *Shigella*, *E. coli*) and does not transmit trypanosomes. * **Sand fly (*Phlebotomus*):** The vector for **Leishmaniasis** (Kala-azar) and Sandfly fever. * **Tick:** Vectors for various diseases like Rickettsial infections (Rocky Mountain Spotted Fever), Babesiosis, and Lyme disease. * *Note on African Sleeping Sickness:* If the question referred to the African variant, the vector would be the **Tsetse fly** (*Glossina*), which transmits *Trypanosoma brucei*. 3. **NEET-PG High-Yield Pearls:** * **Romaña’s Sign:** Unilateral painless periorbital edema, a classic early sign of Chagas disease. * **Chagoma:** A localized inflammatory swelling at the site of entry. * **Chronic Complications:** Dilated cardiomyopathy, **Megaesophagus**, and **Megacolon** (due to destruction of the myenteric plexus). * **C-shaped Trypomastigotes:** Characteristic morphology seen in peripheral blood smears during the acute phase.

Q: Which parasite causes biliary tract obstruction?

Ascaris. **Explanation:** **Ascaris lumbricoides** is the correct answer because it is the most common helminth to cause hepatobiliary complications. Due to its large size (20–35 cm) and high degree of mobility, the adult worm can migrate from the duodenum through the **Ampulla of Vater** into the common bile duct. This leads to mechanical obstruction, resulting in biliary colic, obstructive jaundice, ascending cholangitis, or even acute pancreatitis. In some cases, the worm may die within the duct, acting as a nidus for the formation of pigment gallstones. **Why other options are incorrect:** * **Trichinella spiralis:** This parasite primarily affects skeletal muscle. After ingestion of undercooked meat, the larvae encyst in muscles (like the diaphragm or deltoid), causing myalgia and periorbital edema, but they do not inhabit or obstruct the biliary tract. * **Taenia solium:** The adult tapeworm resides in the small intestine. While it is large, it lacks the migratory "wandering" tendency of *Ascaris*. Its primary clinical concern (other than intestinal infection) is **Cysticercosis**, where larvae form cysts in the brain (NCC) or muscles, not the bile ducts. **High-Yield Clinical Pearls for NEET-PG:** * **Imaging Gold Standard:** Ultrasound is the investigation of choice for biliary ascariasis, often showing a "tube-like" or "railway track" appearance within the bile duct. * **Loeffler’s Syndrome:** Remember that *Ascaris* causes transient pulmonary eosinophilia during its larval migration phase through the lungs. * **Other Biliary Parasites:** While *Ascaris* is the most common cause of *mechanical* obstruction, **Clonorchis sinensis** and **Fasciola hepatica** are other high-yield parasites associated with biliary disease and cholangiocarcinoma.

Q: Which of the following statements regarding Malaria parasites is correct?

Has man as its intermediate host. **Explanation:** The life cycle of *Plasmodium* (the malaria parasite) involves two hosts: a vertebrate host (human) and an invertebrate host (female *Anopheles* mosquito). **1. Why Option A is Correct:** In parasitology, the **Definitive Host** is where the sexual cycle occurs, and the **Intermediate Host** is where the asexual cycle occurs. * **Sexual Cycle (Sporogony):** Occurs in the female *Anopheles* mosquito (Definitive Host). * **Asexual Cycle (Schizogony):** Occurs in humans (Intermediate Host). Therefore, man is the intermediate host. **2. Why Other Options are Incorrect:** * **Option B:** The life cycle alternates between humans and the **female *Anopheles* mosquito**. The tsetse fly is the vector for African Trypanosomiasis (Sleeping Sickness). * **Option C:** While four species were traditionally taught (*P. falciparum, P. vivax, P. malariae, P. ovale*), there are now **five** important species infecting humans, including ***Plasmodium knowlesi*** (a zoonotic species). * **Option D:** Malaria parasites are **difficult to culture**. While the Trager-Jensen method (1976) allows for the *in vitro* cultivation of *P. falciparum*, it is complex, expensive, and not a routine laboratory procedure. **Clinical Pearls for NEET-PG:** * **Infective form to humans:** Sporozoites (injected by mosquito). * **Infective form to mosquito:** Gametocytes (ingested from human blood). * **Exo-erythrocytic stage:** Absent in *P. falciparum*. * **Hypnozoites (Latent liver stage):** Seen in *P. vivax* and *P. ovale*; responsible for relapses. * **Recrudescence:** Seen in *P. falciparum* and *P. malariae* due to sub-therapeutic treatment or waning immunity.

Q: Chagas disease does not involve which of the following organs?

Pancreas. **Explanation:** Chagas disease, caused by the protozoan parasite ***Trypanosoma cruzi***, is characterized by its predilection for muscle and nerve tissues, particularly the autonomic nervous system. **Why Pancreas is the Correct Answer:** The hallmark of chronic Chagas disease is the destruction of **autonomic plexuses** (specifically the Myenteric/Auerbach’s plexus) and direct damage to smooth muscle or cardiac muscle fibers. While *T. cruzi* can theoretically infect various tissues during the acute phase, it does not cause clinical organopathy or structural dysfunction in the **pancreas**. The disease primarily manifests as "Megasyndromes" of the hollow viscera and cardiomyopathy. **Analysis of Incorrect Options:** * **Esophagus:** This is the most common site for gastrointestinal Chagas. Destruction of the myenteric plexus leads to **Megaesophagus**, clinically mimicking achalasia cardia (dysphagia, regurgitation). * **Colon:** The second most common GI site. Loss of inhibitory neurons leads to chronic constipation and **Megacolon**, which can progress to fecaloma or volvulus. * **Duodenum:** Although less common than the esophagus or colon, the duodenum and small intestine can undergo dilatation (**Megaduodenum**) due to the same mechanism of enteric nervous system destruction. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Reduviid bug (Triatomine/Kissing bug). * **Acute Phase Sign:** **Romaña’s sign** (unilateral painless periorbital edema). * **Cardiac Involvement:** Dilated cardiomyopathy and Right Bundle Branch Block (RBBB) are common. * **Diagnosis:** C-shaped trypomastigotes in peripheral blood (acute); Serology or Xenodiagnosis (chronic). * **Treatment:** Nifurtimox or Benznidazole.

Q: Which of the following diseases is transmitted by Phlebotomus argentipes?

Kala-Azar. **Explanation:** The correct answer is **Kala-Azar (Visceral Leishmaniasis)**. *Phlebotomus argentipes* is the primary vector for *Leishmania donovani*, the causative agent of Kala-azar in the Indian subcontinent. These are small, hairy, blood-sucking **sandflies**. They transmit the parasite in its **promastigote** stage through their bite. The disease is characterized by the classic triad of irregular fever, massive splenomegaly, and pancytopenia. **Analysis of Incorrect Options:** * **Epidemic Typhus:** Caused by *Rickettsia prowazekii* and transmitted by the **Human Body Louse** (*Pediculus humanus corporis*). * **Relapsing Fever:** Louse-borne relapsing fever is caused by *Borrelia recurrentis* (transmitted by the **Body Louse**), while tick-borne relapsing fever is caused by *Borrelia* species transmitted by **Ornithodoros ticks**. * **Trench Fever:** Caused by *Bartonella quintana* and is also transmitted by the **Human Body Louse**. **High-Yield NEET-PG Pearls:** * **Vector Habitat:** Sandflies breed in damp soil, cracks in walls, and dark corners; they are "short-distance hoppers" (flight range <100 meters). * **Post-Kala-azar Dermal Leishmaniasis (PKDL):** A non-ulcerative cutaneous condition that develops years after "cured" Visceral Leishmaniasis, acting as a major reservoir for the parasite. * **Drug of Choice:** **Liposomal Amphotericin B** is currently the preferred treatment for Kala-azar in India. * **Diagnostic Gold Standard:** Demonstration of **LD bodies** (Amastigotes) in bone marrow or splenic aspirates.

Q: Which of the following is NOT true about amoebic ulcer?

Perforation is a common complication.. ### Explanation The correct answer is **D. Perforation is a common complication.** While perforation is a serious and life-threatening event in intestinal amoebiasis, it is clinically **uncommon** (occurring in less than 5% of cases). Most cases of intestinal amoebiasis present as chronic diarrhea or dysentery without progressing to full-thickness necrosis and perforation. **Analysis of Options:** * **A. Commonest site is in the ascending colon:** This is **true**. *Entamoeba histolytica* primarily affects the large intestine. The most frequent sites are the **cecum and ascending colon**, followed by the sigmoid colon and rectum, due to the relative stasis of fecal matter which allows the trophozoites to colonize. * **B. Ulcers are typically flask-shaped:** This is **true**. The trophozoites penetrate the mucosa and reach the submucosa. Once there, they spread laterally because the submucosa offers less resistance than the muscularis layer, creating a narrow neck and a broad base—the classic **"flask-shaped" ulcer**. * **C. Paucity of inflammatory cells:** This is **true**. Amoebic ulcers are characterized by **"quiet" or "bland" necrosis**. The trophozoites produce pore-forming proteins (amoebapores) and cysteine proteases that lyse host cells, including neutrophils. This leads to a lack of a robust inflammatory response at the site of the lesion. **High-Yield NEET-PG Pearls:** * **Pathognomonic finding:** Presence of ingested RBCs (erythrophagocytosis) within the trophozoites. * **Stool Microscopy:** Look for quadrinucleate cysts (infective stage) or motile trophozoites with pseudopodia (diagnostic stage in dysentery). * **Amoeboma:** A chronic inflammatory pseudotumor (granuloma) in the colon that can mimic carcinoma. * **Anchovy Sauce Pus:** Characteristic appearance of the aspirate from an Amoebic Liver Abscess (the most common extra-intestinal site).

Q: Which cancer is caused by Schistosoma hematobium?

Urinary bladder cancer. **Explanation:** *Schistosoma haematobium*, a blood fluke, is a well-established risk factor for malignancy. The adult worms reside in the **vesical and pelvic venous plexuses**. The female fluke deposits eggs in the bladder wall, which possess a characteristic **terminal spine**. These eggs provoke a chronic granulomatous inflammatory response, leading to tissue destruction, fibrosis, and eventually, cellular metaplasia. **1. Why Urinary Bladder Cancer is Correct:** Chronic irritation and the release of N-nitroso compounds by the eggs lead to **Squamous Cell Carcinoma (SCC)** of the urinary bladder. This is a high-yield distinction, as the most common type of bladder cancer globally is Transitional Cell Carcinoma (TCC), but *S. haematobium* specifically predisposes to the SCC variant. **2. Why Other Options are Incorrect:** * **Colorectal Cancer:** Associated with *S. mansoni* and *S. japonicum*, which reside in the mesenteric veins and cause intestinal schistosomiasis, but they are not definitive causes of malignancy. * **Bile Duct Carcinoma (Cholangiocarcinoma):** Classically associated with liver flukes like ***Clonorchis sinensis*** and ***Opisthorchis viverrini***, not *Schistosoma*. * **Pancreatic Cancer:** No established causal link exists between Schistosomiasis and pancreatic malignancy. **Clinical Pearls for NEET-PG:** * **Intermediate Host:** Freshwater snails of the genus *Bulinus*. * **Infective Stage:** Cercaria (enters via skin penetration). * **Diagnostic Feature:** Eggs with a **terminal spine** in urine microscopy. * **Treatment:** Praziquantel is the drug of choice. * **Key Association:** *S. haematobium* = Squamous Cell Carcinoma of the bladder.

Question 1

In which host does the flagellar stage of the Leishmania parasite occur?

Accepted Answer

Sandfly

Answer

Man

Answer

Dog

Answer

Hamster

Question 2

Chandler's Index is used for assessing the intensity of infection with which parasite?

Accepted Answer

Ancylostoma

Answer

Filariasis

Answer

Ascariasis

Answer

Guinea worm

Question 3

If parasites are grown in culture with an unknown bacterial associate, what is it called?

Accepted Answer

Xenic culture

Answer

Axenic culture

Answer

Monoxenic culture

Answer

Polyxenic culture

Question 4

Sleeping sickness is caused by which of the following vectors?

Accepted Answer

Reduvid bug

Answer

House fly

Answer

Sand fly

Answer

Tick

Question 5

Which parasite causes biliary tract obstruction?

Accepted Answer

Ascaris

Answer

Trichinella

Answer

Taenia solium

Answer

All of the above

Question 6

Which of the following statements regarding Malaria parasites is correct?

Accepted Answer

Has man as its intermediate host

Answer

Has a life cycle that alternates between man and tse-tse fly

Answer

Has 4 important species in man

Answer

Can be easily cultured in the laboratory

Question 7

Chagas disease does not involve which of the following organs?

Accepted Answer

Pancreas

Answer

Duodenum

Answer

Esophagus

Answer

Colon

Question 8

Which of the following diseases is transmitted by Phlebotomus argentipes?

Accepted Answer

Kala-Azar

Answer

Epidemic typhus

Answer

Relapsing fever

Answer

Trench fever

Question 9

Which of the following is NOT true about amoebic ulcer?

Accepted Answer

Perforation is a common complication.

Answer

Commonest site is in the ascending colon.

Answer

Ulcers are typically flask-shaped.

Answer

There is a paucity of inflammatory cells.

Question 10

Which cancer is caused by Schistosoma hematobium?

Accepted Answer

Urinary bladder cancer

Answer

Colorectal cancer

Answer

Bile duct carcinoma

Answer

Pancreatic cancer

Parasitology — MCQs

Parasitology — MCQs

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