Parasitology Practice Questions

Q: Cysticercus cellulosae is seen in which of the following?

Taenia solium. **Explanation:** The correct answer is **Taenia solium**. **Cysticercus cellulosae** is the larval stage (bladder worm) of *Taenia solium* (Pork tapeworm). In the normal life cycle, pigs ingest eggs, and the larvae develop in their muscles. However, humans can act as accidental intermediate hosts by ingesting eggs through contaminated food or water (autoinfection). This leads to **Cysticercosis**, where these larvae lodge in various tissues, most critically the brain (**Neurocysticercosis**), appearing as "scolex within a cyst" on imaging. **Analysis of Incorrect Options:** * **A. Taenia saginata (Beef tapeworm):** Its larval stage is called **Cysticercus bovis**. Crucially, *T. saginata* does not cause cysticercosis in humans because the eggs are not infectious to humans. * **C. Diphyllobothrium latum (Fish tapeworm):** It has two larval stages: the **Procercoid** (in cyclops) and the **Plerocercoid/Sparganum** (in fish). It is clinically associated with Vitamin B12 deficiency (Megaloblastic anemia). * **D. Schistosoma haematobium (Blood fluke):** This is a trematode. Its infective stage is the **Cercaria**, and it does not have a cysticercus stage. It is primarily associated with urinary schistosomiasis and squamous cell carcinoma of the bladder. **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Human (for both *T. solium* and *T. saginata*). * **Intermediate Host:** Pig (*T. solium*); Cow (*T. saginata*). * **Neurocysticercosis (NCC):** The most common cause of adult-onset seizures in developing countries. MRI shows the "hole-with-dot" appearance. * **Drug of Choice:** Albendazole is preferred for NCC (Praziquantel is an alternative).

Q: A 23-year-old male presented with abdominal pain and bloody diarrhea of one-week duration. What is the diagnosis based on the following rectal mucosa biopsy?

Amoebiasis. ***Amoebiasis*** - **Flask-shaped ulcers** in the rectal mucosa with **Entamoeba histolytica trophozoites** showing **erythrophagocytosis** are pathognomonic features seen on histopathological examination. - The clinical presentation of **bloody diarrhea** with **abdominal pain** in a young male is highly consistent with invasive amoebiasis affecting the colon. *Giardiasis* - Caused by **Giardia lamblia**, which typically affects the **small intestine** and presents with **watery diarrhea**, not bloody stools. - Histologically shows **villous atrophy** and **trophozoites** in the duodenum, not flask-shaped ulcers in the rectum. *Enterobius vermicularis* - **Pinworm infection** primarily causes **perianal itching** and is diagnosed by finding eggs on **cellophane tape test**, not rectal biopsy. - Does not cause **bloody diarrhea** or **invasive colonic lesions** as seen in this case. *Severe bacterial infection* - Bacterial colitis typically shows **neutrophilic infiltration** and **superficial mucosal ulceration**, not the characteristic **flask-shaped ulcers**. - Would not demonstrate **parasitic trophozoites** with **erythrophagocytosis** on histological examination.

Q: Which of the following acts as an intermediate host for hydatid disease?

Man. **Explanation:** Hydatid disease is caused by the larval stage of the cestode **_Echinococcus granulosus_** (Dog tapeworm). Understanding the life cycle is crucial for NEET-PG: 1. **Why Man is the Correct Answer:** In the life cycle of *E. granulosus*, the **Intermediate Host** is the one that harbors the larval stage (hydatid cyst). Naturally, this role is played by sheep and cattle. However, **Humans** act as **accidental intermediate hosts** when they ingest eggs (oncospheres) via contaminated food or water. In humans, the cycle ends (dead-end host) because the larvae cannot be transmitted back to the definitive host. 2. **Why Other Options are Incorrect:** * **B. Dog:** The dog is the **Definitive Host**. It harbors the adult tapeworm in its intestine and passes eggs in its feces. * **D. Foxes:** Along with wolves and jackals, foxes act as definitive hosts for *E. granulosus* or *E. multilocularis*. * **C. Cat:** Cats are generally not involved in the transmission cycle of *E. granulosus*. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Form for Man:** Eggs (Oncospheres) found in dog feces. * **Most Common Site:** Liver (Right lobe), followed by the Lungs. * **Diagnosis:** Casoni’s test (immediate hypersensitivity, now largely replaced), USG (Gharbi’s classification), and "Water Lily sign" on imaging. * **Management:** PAIR (Puncture, Aspiration, Injection, Re-aspiration) and Albendazole. * **Microscopy:** Look for "Hydatid sand" (brood capsules and protoscolices).

Q: Ova in the stool are not of diagnostic significance in which of the following parasitic infections?

Strongyloides. **Explanation:** The correct answer is **Strongyloides stercoralis**. The primary diagnostic stage found in the stool for this parasite is the **Rhabditiform larva**, not the egg (ova). **1. Why Strongyloides is correct:** In *Strongyloides stercoralis* infections, the adult female lives in the mucosal epithelium of the small intestine. She lays eggs that hatch almost immediately within the intestinal mucosa. Therefore, by the time the parasite reaches the stool, it is already in the **L1 (Rhabditiform) larval stage**. Finding eggs in the stool is extremely rare and usually only occurs in cases of severe purgation. **2. Why the other options are incorrect:** * **Trichuris trichiura (Whipworm):** Diagnosis is confirmed by identifying characteristic **barrel-shaped eggs** with bipolar plugs in the stool. * **Ankylostoma duodenale (Hookworm):** Diagnosis relies on finding **oval, segmented, thin-shelled eggs** (usually at the 4-8 cell stage) in the feces. * **Enterobius vermicularis (Pinworm):** While the **NIH swab or Scotch tape test** is the gold standard (detecting eggs on the perianal skin), the eggs are the definitive diagnostic stage. Although rarely seen in routine stool samples, they remain the diagnostic unit of the parasite. **NEET-PG High-Yield Pearls:** * **Strongyloides:** Unique for its **autoinfection** cycle and the ability to cause **Hyperinfection Syndrome** in immunocompromised patients (e.g., those on steroids). * **Larva Currens:** A rapidly moving serpiginous cutaneous eruption pathognomonic for Strongyloidiasis. * **Stool Examination:** If larvae are not found in routine stool, the **Baermann technique** or **Agar plate culture** can be used to increase sensitivity.

Q: Which of the following tests does NOT help in the laboratory diagnosis of Kala-azar?

Immobilization test. **Explanation:** Kala-azar (Visceral Leishmaniasis), caused by *Leishmania donovani*, is diagnosed through direct parasite visualization, serology, or non-specific biochemical tests. **Why "Immobilization Test" is the correct answer:** The **TPI (Treponema Pallidum Immobilization) test** is a highly specific historical test used for the diagnosis of **Syphilis**, not Kala-azar. It involves observing the loss of motility of *T. pallidum* in the presence of patient antibodies. It has no application in leishmaniasis. **Analysis of Incorrect Options:** * **Bone Marrow Examination:** This is the **gold standard** for diagnosis. Aspiration (usually from the sternum or iliac crest) reveals the **Amastigote forms** (LD bodies) within macrophages. It is safer than splenic aspiration. * **Blood Smear Examination:** While less sensitive than bone marrow, a thick or thin peripheral blood smear can demonstrate LD bodies within monocytes or neutrophils, especially in heavy infections. * **Aldehyde Test (Napier’s Test):** This is a non-specific biochemical test based on **hypergammaglobulinemia**. When formalin is added to the patient's serum, it turns opaque and solidifies (like the white of a boiled egg). It becomes positive only after 3 months of infection. **High-Yield Clinical Pearls for NEET-PG:** 1. **Splenic Aspiration:** Most sensitive (95%+) but carries a risk of hemorrhage; Bone marrow is the preferred routine diagnostic. 2. **rK39 Immunochromatographic Test:** The rapid diagnostic test of choice for field use (high sensitivity and specificity). 3. **Culture Medium:** NNN (Novy-MacNeal-Nicolle) medium is used to grow the **Promastigote** form. 4. **Montenegro (Leishmanin) Skin Test:** It is **negative** in active Kala-azar and becomes positive only after recovery (delayed hypersensitivity).

Q: Schistosoma is transmitted by which of the following?

Snail. **Explanation:** **Schistosoma** (Blood Flukes) are unique trematodes that cause Schistosomiasis. The correct answer is **Snail** because all trematodes (flukes) require a specific freshwater snail as their **obligate intermediate host** to complete their life cycle. 1. **Why Snail is Correct:** In the life cycle, eggs excreted in human feces or urine hatch into **miracidia** upon reaching water. These miracidia must infect a specific snail (e.g., *Biomphalaria* for *S. mansoni*, *Bulinus* for *S. haematobium*). Inside the snail, they undergo asexual reproduction to emerge as **Cercariae**, which are the infective stage for humans. Infection occurs via direct **skin penetration** while wading in contaminated water. 2. **Why other options are incorrect:** * **Cyclops:** This is the intermediate host for *Dracunculus medinensis* (Guinea worm), *Diphyllobothrium latum* (Fish tapeworm), and *Gnathostoma spinigerum*. * **Fish:** Freshwater fish act as the second intermediate host for *Clonorchis sinensis* (Chinese liver fluke) and *Opisthorchis*, but not for Schistosoma. * **Cattle:** Cattle serve as the intermediate host for *Taenia saginata* (Beef tapeworm). **High-Yield Clinical Pearls for NEET-PG:** * **Infective stage:** Cercaria (specifically fork-tailed cercaria). * **Diagnostic stage:** Non-operculated eggs with spines (e.g., *S. haematobium* has a **terminal spine**). * **Unique feature:** Unlike other flukes, Schistosomes are **dioecious** (separate sexes) and do not have a redia stage in their life cycle. * **Clinical association:** *S. haematobium* is strongly linked to **Squamous Cell Carcinoma of the bladder**. * **Drug of Choice:** Praziquantel.

Q: What is the common name for Echinococcus granulosus?

Hymenolepis nana. **Explanation:** The question asks for the common name of *Echinococcus granulosus*. However, based on the provided answer key, there is a discrepancy: **Hymenolepis nana** is the common name for the **Dwarf Tapeworm**, not *Echinococcus granulosus*. The common name for ***Echinococcus granulosus*** is the **Hydatid Tapeworm** or Dog Tapeworm. Assuming the question intends to test the identification of common names for major helminths: 1. **Hymenolepis nana (Correct per key):** Known as the **Dwarf Tapeworm**, it is the smallest intestinal cestode infecting humans. It is unique because it does not require an intermediate host (direct life cycle) and is the most common cause of all cestode infections worldwide. 2. **Echinococcus granulosus (Option A):** Known as the **Hydatid Tapeworm**. It causes Cystic Echinococcosis (Hydatid disease), typically presenting as slow-growing cysts in the liver or lungs. 3. **Loa loa (Option B):** Known as the **African Eye Worm**. It is a nematode transmitted by the *Chrysops* (deer fly) and is famous for causing "Calabar swellings" and migrating across the subconjunctiva of the eye. 4. **Schistosoma mansoni (Option D):** Known as **Manson’s Blood Fluke**. It resides in the mesenteric veins and is a major cause of intestinal schistosomiasis and portal hypertension. **NEET-PG Clinical Pearls:** * **H. nana:** Only tapeworm that can complete its entire life cycle in a single host (Human). * **E. granulosus:** Diagnosis involves the "Casoni skin test" (historical) and imaging showing "water lily sign" or "hydatid sand." * **Treatment:** Albendazole is the drug of choice for *Echinococcus*, while Praziquantel is used for *H. nana* and *Schistosoma*.

Q: Terminal spined eggs are seen in which parasite?

Schistosoma haematobium. The identification of *Schistosoma* species is a high-yield topic in NEET-PG, primarily based on the morphology of their eggs. **Correct Answer: A. Schistosoma haematobium** *Schistosoma haematobium* is uniquely characterized by eggs that possess a distinct **terminal spine** at one end. These eggs are typically excreted in the **urine** (and occasionally feces). Clinically, this parasite inhabits the vesical venous plexuses, leading to hematuria and an increased risk of squamous cell carcinoma of the urinary bladder. **Explanation of Incorrect Options:** * **B. Schistosoma mansoni:** These eggs are characterized by a prominent **lateral spine**. They are found in the feces and are associated with intestinal schistosomiasis and portal hypertension. * **C. Schistosoma japonicum:** These eggs are more rounded/oval and possess a very small, inconspicuous **lateral knob** (rudimentary spine) rather than a prominent spine. * **D. Clonorchis sinensis:** Also known as the Chinese Liver Fluke, its eggs are much smaller, flask-shaped, and possess an **operculum** (lid) at one pole and a small knob at the other, but they do not have spines. **High-Yield Clinical Pearls for NEET-PG:** * **Intermediate Host:** All Schistosomes require **snails** as intermediate hosts (e.g., *Bulinus* for *S. haematobium*). * **Infective Stage:** **Cercaria** (penetrates unbroken skin during swimming). * **Diagnostic Test:** Urine microscopy (10 AM to 2 PM sample) for *S. haematobium*; Kat-Katz technique for stool samples. * **Drug of Choice:** **Praziquantel** is the gold standard for all Schistosoma species.

Q: Which of the following organisms uses man as an intermediate host?

Plasmodium. ### Explanation In parasitology, the classification of hosts is determined by the stage of the parasite's life cycle: * **Definitive Host:** Where the **sexual cycle** occurs or the adult parasite resides. * **Intermediate Host:** Where the **asexual cycle** occurs or the larval stages develop. **Why Plasmodium is Correct:** In the life cycle of *Plasmodium* (Malaria), the **sexual cycle (sporogony)** occurs within the female *Anopheles* mosquito, making it the definitive host. The **asexual cycle (schizogony)** occurs in humans (hepatic and erythrocytic stages), thus making **man the intermediate host**. **Analysis of Incorrect Options:** * **Brugia malayi & Wuchereria bancrofti:** For these filarial nematodes, **man is the definitive host** because the adult worms reside in the human lymphatic system. The mosquito acts as the intermediate host where larval development (L1 to L3) occurs. * **Taenia saginata (Beef Tapeworm):** **Man is the definitive host** (harbors the adult worm in the intestine). Cattle serve as the intermediate host. *Note: In Taenia solium, man can be both the definitive host (taeniasis) and the accidental intermediate host (cysticercosis).* **NEET-PG High-Yield Pearls:** * **Man as Intermediate Host:** Remember the mnemonic **"MPT"** — **M**alaria (*Plasmodium*), **P**neumocystis (rarely asked this way), and **T**oxoplasma. Also includes *Echinococcus granulosus* (Hydatid disease). * **Exception:** In *Hymenolepis nana*, man serves as both definitive and intermediate host in the same individual. * **Accidental Host:** Man is the "dead-end" intermediate host for *Echinococcus granulosus* and *Toxocara canis*.

Q: A man presented with diarrhea and lower abdominal pain. The stool is heme-positive. What is the investigation of choice for amoebiasis?

Microscopy and ELISA. **Explanation:** The diagnosis of intestinal amoebiasis (caused by *Entamoeba histolytica*) relies on distinguishing the pathogen from non-pathogenic commensals like *E. dispar*. 1. **Why "Microscopy and ELISA" is correct:** While **microscopy** is the traditional first-line test to visualize trophozoites (containing ingested RBCs) or quadrinucleate cysts, it has low sensitivity (approx. 60%) and cannot morphologically distinguish *E. histolytica* from *E. dispar*. **ELISA** for fecal antigen detection (specifically targeting the Gal/GalNAc lectin) provides high specificity and sensitivity, allowing for definitive identification of the pathogen. Combining both methods maximizes diagnostic yield and accuracy. 2. **Why other options are incorrect:** * **ELISA (Option A):** While highly specific, relying solely on ELISA may miss cases if the antigen load is low; microscopy remains a necessary screening tool. * **Colonoscopy (Option B):** This is an invasive procedure. While it may show characteristic "flask-shaped ulcers," it is reserved for cases where stool studies are negative but clinical suspicion remains high. * **Microscopy (Option C):** Insufficient as a standalone test due to its inability to differentiate species and its dependence on the skill of the microscopist. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic finding:** Trophozoites with **ingested RBCs** (Erythrophagocytosis) in stool microscopy. * **Stain of choice:** Iron-hematoxylin or Trichrome stain. * **Serology:** Serum antibody ELISA is more useful for **Extra-intestinal amoebiasis** (e.g., Amoebic Liver Abscess) than for intestinal disease. * **Treatment:** Luminal agents (Diloxanide furoate/Paromomycin) are needed even in asymptomatic cyst passers to prevent transmission.

Question 1

Cysticercus cellulosae is seen in which of the following?

Accepted Answer

Taenia solium

Answer

Taenia saginata

Answer

Diphyllobothrium latum

Answer

Schistosoma haematobium

Question 2

A 23-year-old male presented with abdominal pain and bloody diarrhea of one-week duration. What is the diagnosis based on the following rectal mucosa biopsy?

Accepted Answer

Amoebiasis

Answer

Giardiasis

Answer

Enterobius vermicularis

Answer

Severe bacterial infection

Question 3

Which of the following acts as an intermediate host for hydatid disease?

Accepted Answer

Man

Answer

Dog

Answer

Cat

Answer

Foxes

Question 4

Ova in the stool are not of diagnostic significance in which of the following parasitic infections?

Accepted Answer

Strongyloides

Answer

Enterobius

Answer

Trichuris

Answer

Ankylostoma

Question 5

Which of the following tests does NOT help in the laboratory diagnosis of Kala-azar?

Accepted Answer

Immobilization test

Answer

Bone marrow examination

Answer

Blood smear examination

Answer

Aldehyde test

Question 6

Schistosoma is transmitted by which of the following?

Accepted Answer

Snail

Answer

Cyclops

Answer

Fish

Answer

Cattle

Question 7

What is the common name for Echinococcus granulosus?

Accepted Answer

Hymenolepis nana

Answer

Echinococcus granulosus

Answer

Loa Loa

Answer

Schistosoma mansoni

Question 8

Terminal spined eggs are seen in which parasite?

Accepted Answer

Schistosoma haematobium

Answer

Schistosoma mansoni

Answer

Schistosoma Japonicum

Answer

Chlonorchis sinensis

Question 9

Which of the following organisms uses man as an intermediate host?

Accepted Answer

Plasmodium

Answer

Brugia malayi

Answer

Wuchereria bancrofti

Answer

Taenia saginata

Question 10

A man presented with diarrhea and lower abdominal pain. The stool is heme-positive. What is the investigation of choice for amoebiasis?

Accepted Answer

Microscopy and ELISA

Answer

ELISA

Answer

Colonoscopy

Answer

Microscopy

Parasitology — MCQs

Parasitology — MCQs

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