Parasitology Practice Questions

Q: A 30-year-old man presents with subcutaneous itchy nodules over the left iliac crest. On examination, the nodules are firm, non-tender, and mobile. Skin scrapings contain microfilariae and adult worms. Which parasite is most likely responsible?

Onchocerca volvulus. ### Explanation The clinical presentation of firm, non-tender, mobile subcutaneous nodules (known as **Onchocercomata**) containing both adult worms and microfilariae is pathognomonic for **_Onchocerca volvulus_**. **1. Why the Correct Answer is Right:** _Onchocerca volvulus_ (the causative agent of River Blindness) typically presents with subcutaneous nodules over bony prominences (like the iliac crest or skull). The adult worms reside within these fibrous nodules, where they mate and release microfilariae. Diagnosis is confirmed by identifying microfilariae in **skin snips** (scrapings) or by finding adult worms in an excised nodule. **2. Why the Incorrect Options are Wrong:** * **_Loa loa_ (African Eye Worm):** Characterized by transient, localized subcutaneous swellings called **Calabar swellings**. Adult worms migrate through the subconjunctiva of the eye. Microfilariae are found in the **blood**, not skin scrapings. * **_Brugia malayi_:** A cause of lymphatic filariasis. It primarily affects the lymphatic system, leading to lymphadenitis and elephantiasis of the lower limbs. Microfilariae are found in the **blood** (nocturnal periodicity). * **_Mansonella streptocerca_:** While it can cause itchy skin rashes and hypopigmented macules, it rarely forms the distinct, firm, mobile nodules (onchocercomata) characteristic of _O. volvulus_. **3. High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Blackfly (_Simulium_). * **Mazzotti Reaction:** A severe inflammatory response (fever, rash, tachycardia) occurring after treatment with Diethylcarbamazine (DEC) due to the rapid killing of microfilariae. * **Drug of Choice:** **Ivermectin** (Note: DEC is contraindicated in Onchocerciasis as it can worsen ocular damage). * **Ocular Complication:** "Snowflake" opacities leading to Sclerosing Keratitis (River Blindness).

Q: Man is the definitive host for which of the following parasites?

Filaria. ### Explanation In medical parasitology, the **Definitive Host (DH)** is defined as the host in which the parasite undergoes its **sexual cycle** or reaches adult maturity. An **Intermediate Host (IH)** is one where the parasite undergoes asexual reproduction or larval development. **Correct Option: B. Filaria** In the life cycle of *Wuchereria bancrofti* and *Brugia malayi*, **humans are the definitive host** because they harbor the adult worms in the lymphatic system, where sexual reproduction occurs. The mosquito (Culex, Anopheles, or Aedes) serves as the intermediate host, harboring the larval stages (L1 to L3). **Incorrect Options:** * **A. Malaria (*Plasmodium*):** In malaria, the **Female Anopheles mosquito is the definitive host** because the sexual cycle (sporogony) occurs within the mosquito. Humans are the **intermediate host** because only asexual reproduction (schizogony) occurs in human liver and red blood cells. * **C. Measles:** This is a viral infection, not a parasitic one. Viruses do not follow the "definitive/intermediate host" classification used for parasites; humans are the natural reservoir and only host. * **D. All:** Incorrect, as the host status differs between Malaria and Filaria. **High-Yield Clinical Pearls for NEET-PG:** * **Exception to the Rule:** For most helminths (like Filaria, *Taenia solium*, *Ascaris*), man is the DH. The major exception is **Hydatid disease (*Echinococcus granulosus*)**, where the dog is the DH and man is the **accidental intermediate host** (dead-end host). * **Toxoplasmosis:** Cats are the DH; humans are IH. * **Diagnostic Stage of Filaria:** Microfilariae (detected in peripheral blood, usually with nocturnal periodicity). * **Drug of Choice for Filariasis:** Diethylcarbamazine (DEC).

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.

Question 1

A 30-year-old man presents with subcutaneous itchy nodules over the left iliac crest. On examination, the nodules are firm, non-tender, and mobile. Skin scrapings contain microfilariae and adult worms. Which parasite is most likely responsible?

Accepted Answer

Onchocerca volvulus

Answer

Loa Loa

Answer

Brugia malayi

Answer

Mansonella streptocerca

Question 2

Which of the following is a neuropathogenic amoeba?

Accepted Answer

Acanthamoeba

Answer

Entamoeba coli

Answer

Naegleria

Answer

Entamoeba histolytica

Question 3

Man is the definitive host for which of the following parasites?

Accepted Answer

Filaria

Answer

Malaria

Answer

Measles

Answer

All

Question 4

Human eosinophilic meningitis is most commonly caused by?

Accepted Answer

Angiostrongyliasis

Answer

Neurocysticercosis

Answer

Coccidiodomycosis

Answer

Schistosomiasis

Question 5

Which of the following parasites can enter through intact skin?

Accepted Answer

Strongyloides

Answer

Giardia

Answer

Whipworm

Answer

Trichinella

Question 6

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 7

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

Accepted Answer

Falciparum malaria

Answer

Leishmaniasis

Answer

Trypanosomiasis

Answer

Leptospirosis

Question 8

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 9

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

Accepted Answer

Sheep

Answer

Human

Answer

Dog

Answer

Fox

Question 10

Eosinophilic meningoencephalitis is caused by which of the following?

Accepted Answer

Angiostrongylus

Answer

Acanthamoeba

Answer

Naegleria

Answer

Toxoplasma

Parasitology — MCQs

Parasitology — MCQs

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