Parasitology Practice Questions

Q: Human eosinophilic meningitis is most commonly caused by?

Angiostrongyliasis. **Explanation:** **Angiostrongyliasis** (specifically caused by *Angiostrongylus cantonensis*, the rat lungworm) is the most common cause of human eosinophilic meningitis worldwide. The condition is defined by the presence of ≥10 eosinophils/µL in the cerebrospinal fluid (CSF) or a total CSF differential count of ≥10% eosinophils. Humans are accidental hosts who acquire the infection by consuming raw mollusks (snails/slugs) or contaminated vegetables containing third-stage larvae. The larvae migrate to the CNS but cannot complete their life cycle in humans, leading to an intense eosinophilic inflammatory response. **Analysis of Incorrect Options:** * **Neurocysticercosis (B):** Caused by *Taenia solium* larvae. While it is the most common parasitic infection of the CNS globally and can cause seizures, it typically presents with a lymphocytic pleocytosis. Eosinophilia in the CSF is rare. * **Coccidioidomycosis (C):** A fungal infection. While it can cause chronic meningitis with occasional CSF eosinophilia, it is far less common than *Angiostrongylus* as a primary cause of eosinophilic meningitis. * **Schistosomiasis (D):** Can cause neuroschistosomiasis (usually spinal cord involvement), but it is not a classic or common cause of eosinophilic meningitis. **High-Yield Clinical Pearls for NEET-PG:** * **Definition:** CSF Eosinophilia = ≥10 eosinophils/mm³. * **Intermediate Host:** Apple snails (*Pila* species) and slugs. * **Definitive Host:** Rats (larvae reside in pulmonary arteries). * **Clinical Presentation:** Severe headache, neck stiffness, and paresthesia. * **Diagnosis:** Primarily clinical and travel history; ELISA for antibodies. * **Treatment:** Supportive care and corticosteroids; the role of anthelmintics (Albendazole) is controversial as killing larvae may worsen inflammation.

Q: Which of the following parasites can enter through intact skin?

Strongyloides. **Explanation:** The correct answer is **Strongyloides stercoralis**. The primary mode of infection for certain helminths is the penetration of **intact skin** (usually of the feet) by infective larvae present in contaminated soil. **Why Strongyloides is correct:** * The infective stage of *Strongyloides stercoralis* is the **filariform larva**. These larvae possess proteolytic enzymes that allow them to penetrate human skin directly. * Once inside, they enter the venous circulation, travel to the lungs, ascend the tracheobronchial tree, are swallowed, and finally mature in the small intestine. **Why the other options are incorrect:** * **Giardia lamblia:** An intestinal protozoan transmitted via the **fecal-oral route** through the ingestion of mature cysts in contaminated water or food. * **Whipworm (*Trichuris trichiura*):** Transmission occurs via the **fecal-oral route** through the ingestion of embryonated eggs from soil. There is no tissue migration phase. * **Trichinella spiralis:** Infection occurs by **ingesting undercooked meat** (usually pork) containing encysted larvae. **NEET-PG High-Yield Pearls:** 1. **Mnemonic for Skin Penetrators:** Remember **"S-A-N-D"** — **S**trongyloides, **A**ncylostoma duodenale (Hookworm), **N**ecator americanus (Hookworm), and **D**ermatobia hominis (Botfly). *Schistosoma* (Blood flukes) also enter through skin (cercariae). 2. **Autoinfection:** *Strongyloides* is unique because it can cause **internal autoinfection**, leading to "Hyperinfection Syndrome" in immunocompromised patients (e.g., those on steroids). 3. **Larva Currens:** The rapid, linear skin rash caused by migrating *Strongyloides* larvae is a classic clinical sign.

Q: Which of the human intestinal parasitic nematodes does not infest the small bowel?

Trichuris trichiura. ### Explanation The correct answer is **D. Trichuris trichiura**. The primary site of infestation for intestinal nematodes is determined by their life cycle and physiological requirements. Most common nematodes inhabit the small intestine, but **Trichuris trichiura (Whipworm)** is a notable exception [1]. **1. Why Trichuris trichiura is correct:** * **Habitat:** Unlike the other options, the adult whipworm resides in the **large intestine**, specifically the **cecum** and ascending colon [1]. * **Pathophysiology:** The anterior thin end of the worm embeds into the mucosal lining of the colon. Heavy infestations can lead to "Trichuris dysentery syndrome" and, classically, **rectal prolapse** in children [1]. **2. Why the other options are incorrect:** * **Ascaris lumbricoides (Roundworm):** Adult worms live in the lumen of the **jejunum** (upper small intestine). They are the largest nematodes and can cause intestinal obstruction at this site. * **Necator americanus (Hookworm):** These parasites inhabit the **upper small intestine**, where they attach to the villi of the duodenum and jejunum to suck blood, leading to iron-deficiency anemia [4]. * **Strongyloides stercoralis:** The adult female worms burrow into the mucosal epithelium of the **duodenum and jejunum** [2]. It is unique because it can cause autoinfection. **High-Yield NEET-PG Pearls:** * **Large Intestine Nematodes:** Remember the "Big Two"—*Trichuris trichiura* (Whipworm) and *Enterobius vermicularis* (Pinworm) [1]. * **Small Intestine Nematodes:** *Ascaris*, Hookworms (*Ancylostoma* and *Necator*), and *Strongyloides* [4]. * **Egg Morphology:** *Trichuris* eggs are characteristically **barrel-shaped with bipolar mucus plugs**. * **Treatment:** Albendazole or Mebendazole are the drugs of choice for most intestinal nematodes [3].

Q: What is the intermediate host for the parasite that causes hydatid disease?

Sheep. Hydatid disease is caused by the cestode **_Echinococcus granulosus_**. Understanding its life cycle is crucial for NEET-PG, as it involves a distinct transition between definitive and intermediate hosts. ### **Explanation of the Correct Answer** **C. Sheep:** In the natural life cycle, sheep (and other herbivores) serve as the **Intermediate Host**. They ingest eggs passed in the feces of the definitive host. The eggs hatch into oncospheres, migrate to visceral organs (primarily the liver), and develop into **Hydatid Cysts** (the larval stage). ### **Analysis of Incorrect Options** * **A. Human:** Humans are considered **Accidental Intermediate Hosts**. We are a "dead-end" for the parasite because the life cycle is broken (dogs do not typically consume human viscera). While the disease occurs in humans, sheep remain the primary natural intermediate host. * **B. Dog:** The dog (and other canids) is the **Definitive Host**. It harbors the adult tapeworm in its small intestine. It becomes infected by eating the hydatid cysts found in the organs of the intermediate host. * **C. Fox:** Foxes are the definitive hosts for _Echinococcus multilocularis_, which causes alveolar hydatid disease, but they are not the primary host for _E. granulosus_. ### **High-Yield Clinical Pearls for NEET-PG** * **Infective Form to Humans:** Embryonated eggs (found in dog feces). * **Diagnostic Classic:** **Casoni’s Test** (immediate hypersensitivity; now largely replaced by serology/ELISA). * **Radiology:** Look for **"Water-lily sign"** (collapsed germinal membrane) or **"Eggshell calcification"** on X-ray/CT. * **Management:** **PAIR** technique (Puncture, Aspiration, Injection of scolicidal agent like hypertonic saline, Re-aspiration). * **Complication:** Rupture of the cyst can lead to potentially fatal **Anaphylaxis**.

Q: Eosinophilic meningoencephalitis is caused by which of the following?

Angiostrongylus. **Explanation:** The correct answer is **Angiostrongylus cantonensis** (the rat lungworm). **1. Why Angiostrongylus is correct:** *Angiostrongylus cantonensis* is the most common cause of **Eosinophilic Meningoencephalitis** worldwide. Humans are accidental hosts, typically infected by ingesting larvae in raw/undercooked snails, slugs, or contaminated vegetables. Once ingested, the larvae migrate to the central nervous system (CNS). Because they cannot complete their life cycle in humans, they die in the brain, triggering a profound inflammatory response characterized by a high count of **eosinophils in the cerebrospinal fluid (CSF)** (usually >10% of the total CSF leukocyte count). **2. Why other options are incorrect:** * **Acanthamoeba:** Causes **Granulomatous Amoebic Encephalitis (GAE)**, a subacute to chronic infection typically seen in immunocompromised individuals. It is also associated with amoebic keratitis in contact lens users. * **Naegleria fowleri:** Causes **Primary Amoebic Meningoencephalitis (PAM)**. This is an acute, fulminant, and highly fatal infection acquired through swimming in warm freshwater. The CSF shows a neutrophilic (not eosinophilic) pleocytosis. * **Toxoplasma gondii:** Typically causes **Ring-enhancing lesions** (brain abscesses) in HIV/AIDS patients. It does not present as a primary eosinophilic meningitis. **3. NEET-PG High-Yield Pearls:** * **Definition:** Eosinophilic meningitis is defined as >10 eosinophils/mm³ in CSF or eosinophils accounting for >10% of CSF WBCs. * **Other causes:** *Gnathostoma spinigerum*, *Baylisascaris procyonis*, and Neurocysticercosis (occasionally). * **Clinical Clue:** History of eating raw snails or slugs followed by severe headache and meningeal signs. * **Treatment:** Primarily supportive; corticosteroids are used to reduce inflammation caused by dying worms. Albendazole is controversial as it may worsen inflammation.

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).

Question 1

Human eosinophilic meningitis is most commonly caused by?

Accepted Answer

Angiostrongyliasis

Answer

Neurocysticercosis

Answer

Coccidiodomycosis

Answer

Schistosomiasis

Question 2

Which of the following parasites can enter through intact skin?

Accepted Answer

Strongyloides

Answer

Giardia

Answer

Whipworm

Answer

Trichinella

Question 3

Hemolysis is most severe with Plasmodium falciparum infection compared to other malarial parasites because of which of the following?

Accepted Answer

Ability of the parasite to infect red blood cells of all ages

Answer

Associated gram-negative bacteremia

Answer

Ability of the organism to infect selectively reticulocytes

Answer

Ability of the organism to escape immune recognition by the immune system

Question 4

Black water fever is seen in which of the following conditions?

Accepted Answer

Falciparum malaria

Answer

Leishmaniasis

Answer

Trypanosomiasis

Answer

Leptospirosis

Question 5

Which of the human intestinal parasitic nematodes does not infest the small bowel?

Accepted Answer

Trichuris trichiura

Answer

Ascaris lumbricoides

Answer

Necator americanus

Answer

Strogyloides stercoralis

Question 6

What is the intermediate host for the parasite that causes hydatid disease?

Accepted Answer

Sheep

Answer

Human

Answer

Dog

Answer

Fox

Question 7

Eosinophilic meningoencephalitis is caused by which of the following?

Accepted Answer

Angiostrongylus

Answer

Acanthamoeba

Answer

Naegleria

Answer

Toxoplasma

Question 8

Cysticercus cellulosae is seen in which of the following?

Accepted Answer

Taenia solium

Answer

Taenia saginata

Answer

Diphyllobothrium latum

Answer

Schistosoma haematobium

Question 9

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 10

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

Accepted Answer

Man

Answer

Dog

Answer

Cat

Answer

Foxes

Parasitology — MCQs

Parasitology — MCQs

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