Parasitology Practice Questions

Q: Auto-infection is characteristic of which of the following helminths?

Enterobius vermicularis. ### Explanation **Correct Answer: D. Enterobius vermicularis** **Mechanism of Auto-infection:** Auto-infection occurs when an individual serves as both the source and the host for a new cycle of infection without the parasite needing to undergo a developmental stage in the external environment. In **Enterobius vermicularis** (Pinworm), the female migrates to the perianal skin at night to lay eggs. These eggs become infective within 4–6 hours. Intense itching (pruritus ani) leads to scratching, and the eggs are transferred to the mouth via contaminated fingers (**fecal-oral route**). Additionally, **retro-infection** can occur when larvae hatch on the perianal skin and migrate back into the colon. **Why the other options are incorrect:** * **A. Trichuris trichura (Whipworm):** Eggs are passed unembryonated in feces and require approximately 2–4 weeks in warm, moist soil to become infective. Direct person-to-person transmission is impossible. * **B. Ankylostoma duodenale (Hookworm):** Eggs hatch into rhabditiform larvae in the soil, which then transform into infective filariform larvae. Infection occurs via skin penetration, not direct ingestion of eggs from the host. * **C. Ascaris lumbricoides (Roundworm):** Eggs must undergo embryonation in the soil (taking 2–3 weeks) before they become infective. Freshly passed eggs are not infectious. **NEET-PG High-Yield Pearls:** * **List of Helminths showing Auto-infection:** *Enterobius vermicularis*, *Strongyloides stercoralis* (internal auto-infection), *Hymenolepis nana*, and *Taenia solium*. * **Diagnostic Gold Standard:** NIH Swab or Scotch Tape (Cellophane tape) test, performed early in the morning before bathing. * **Drug of Choice:** Albendazole or Mebendazole (treat the entire family to prevent reinfection). * **Clinical Sign:** Perianal pruritus and nocturnal enuresis in children.

Q: Which enzyme is utilized by the rapid diagnostic test for P. falciparum?

LDH. ### Explanation The Rapid Diagnostic Test (RDT) for Malaria is an immunochromatographic assay that detects specific plasmodial antigens in the blood. **Why LDH is the correct answer:** **Parasite Lactate Dehydrogenase (pLDH)** is a functional enzyme produced only by **living** malaria parasites. It is part of the parasite's glycolytic pathway. RDTs using monoclonal antibodies against pLDH can detect all four major human malaria species (*P. falciparum, P. vivax, P. ovale,* and *P. malariae*). Because pLDH is cleared from the blood shortly after the parasite dies, it is an excellent marker for monitoring **treatment efficacy** and identifying active infection. **Analysis of Incorrect Options:** * **HRP-2 (Histidine-Rich Protein 2):** While this is the most common antigen used to detect *P. falciparum*, it is a **protein**, not an enzyme. Furthermore, HRP-2 can persist in the bloodstream for weeks after successful treatment, leading to false positives. * **SGOT (Serum Glutamic Oxaloacetic Transaminase):** Also known as AST, this is a human liver enzyme. It may be elevated in malaria due to liver involvement or hemolysis, but it is not a diagnostic marker used in RDTs. * **Peroxidase:** This enzyme is used in various laboratory assays (like ELISA) as a signaling molecule, but it is not a specific parasite-derived antigen used for malaria diagnosis. **Clinical Pearls for NEET-PG:** * **HRP-2:** Specific for *P. falciparum* only. * **pLDH:** Can be "Pan-specific" (all species) or "Species-specific" (e.g., *P.f.* or *P.v.*). * **Prozone Effect:** High parasitemia can sometimes cause a false-negative RDT result. * **Gold Standard:** Microscopic examination of peripheral blood smears (Thick for detection, Thin for species identification) remains the gold standard.

Q: All of the following are true regarding transfusion malaria EXCEPT:

Sporozoites transmit it. ### Explanation The correct answer is **A. Sporozoites transmit it**. In **transfusion malaria**, the infection is acquired through the transfusion of blood containing the parasite. The key concept here is the life cycle stage involved: 1. **Why Option A is the correct (false) statement:** Sporozoites are the infective stage found in the salivary glands of the female *Anopheles* mosquito. They are introduced into the human body during a mosquito bite and immediately head to the liver. In blood transfusion, the donor’s blood contains **erythrocytic stages (merozoites/trophozoites)**, not sporozoites. Therefore, transfusion malaria is transmitted by merozoites. 2. **Why Option B is wrong (True statement):** The incubation period is shorter because the parasite bypasses the time-consuming liver phase (pre-erythrocytic schizogony) and enters the bloodstream directly to start infecting RBCs. 3. **Why Option C is wrong (True statement):** As mentioned, the infection is initiated by the asexual erythrocytic stages (merozoites) present in the donor's red cells. 4. **Why Option D is wrong (True statement):** Since sporozoites are absent, there is no **pre-erythrocytic (liver) stage**. Consequently, there is no risk of **relapse** (hypnozoites) in *P. vivax* or *P. ovale* infections acquired via transfusion, as hypnozoites only form during the liver stage. ### High-Yield Clinical Pearls for NEET-PG: * **Relapse vs. Recrudescence:** Transfusion malaria cannot cause relapse because there is no hepatic phase. * **Screening:** *P. falciparum* is the most common species transmitted via transfusion. * **Storage:** Malarial parasites can survive in blood stored at 4°C for up to 2–3 weeks. * **Drug of Choice:** Since there is no liver stage, **Primaquine is NOT required** for radical cure in transfusion-induced *P. vivax*; Chloroquine alone is sufficient.

Q: A definitive diagnosis of ascariasis can be made by observing which of the following?

An adult worm passed during a bowel movement. ### Explanation **1. Why Option A is Correct:** A definitive diagnosis in parasitology requires the direct visualization of the parasite (eggs, larvae, or adult worms) from clinical specimens. *Ascaris lumbricoides* is the largest intestinal nematode. The most common and definitive ways to diagnose it are by identifying the characteristic **bile-stained eggs** in a stool microscopy or by the **gross identification of an adult worm** passed via the anus, mouth, or nose. Seeing the adult worm provides an indisputable, "gold standard" visual confirmation of the infection. **2. Why Other Options are Incorrect:** * **Option B:** Larvae are microscopic and cannot be seen on a standard X-ray. While X-rays may show "Loeffler’s syndrome" (transient pulmonary infiltrates), this is a non-specific radiological finding, not a definitive visualization of the parasite. * **Option C:** Unlike *Strongyloides stercoralis*, where larvae are the diagnostic stage in stool, *Ascaris* eggs hatch in the small intestine, and the larvae immediately migrate to the lungs. Therefore, **larvae are not typically found in stool samples**; only eggs or adult worms are. * **Option D:** Eosinophilia is a common finding during the larval migration phase (Loeffler’s syndrome), but it is a non-specific systemic response seen in many parasitic infections and allergic conditions. It is suggestive, not definitive. **3. NEET-PG High-Yield Pearls:** * **Diagnostic Stage:** Eggs in feces (most common) or adult worms. * **Infective Stage:** Embryonated eggs (not fresh eggs). * **Loeffler’s Syndrome:** Characterized by fever, cough, wheezing, and eosinophilia during the lung migration phase. * **Complications:** Most common is **Intestinal Obstruction** (at the ileocecal valve) and **Biliary Ascariasis**. * **Deworming:** Albendazole is the drug of choice; it works by inhibiting microtubule synthesis.

Q: Which of the following amoeba species is known to cause meningitis?

Acanthamoeba. **Explanation:** The correct answer is **C. Acanthamoeba**. **Why Acanthamoeba is correct:** Acanthamoeba belongs to the group of **Free-Living Amoebae (FLA)**, which are ubiquitous in soil and water. Unlike intestinal amoebae, these species can cross the blood-brain barrier. Acanthamoeba specifically causes **Granulomatous Amoebic Encephalitis (GAE)**, a subacute to chronic meningitis/encephalitis typically seen in immunocompromised individuals. It enters the body through the lower respiratory tract or skin ulcers and spreads hematogenously to the CNS. **Why the other options are incorrect:** * **A. Dientamoeba:** *Dientamoeba fragilis* is a flagellated protozoan (historically classified with amoebae) that inhabits the large intestine. It causes diarrhea and abdominal pain but does not disseminate to the CNS. * **B. Entamoeba:** While *Entamoeba histolytica* can cause extraintestinal disease (most commonly Amoebic Liver Abscess), it primarily causes intestinal amoebiasis. Brain abscesses are a rare complication, but it does not typically present as meningitis. * **D. Iodamoeba:** *Iodamoeba bütschlii* is considered a non-pathogenic commensal of the human intestine. Its presence indicates fecal contamination of food or water but does not cause clinical disease or meningitis. **High-Yield Clinical Pearls for NEET-PG:** * **Acanthamoeba** is also the leading cause of **Amoebic Keratitis**, especially in contact lens users (associated with contaminated cleaning solutions). * **Naegleria fowleri** (the "brain-eating amoeba") causes **Primary Amoebic Meningoencephalitis (PAM)**, which is acute, fulminant, and usually fatal, typically following swimming in warm freshwater. * **Diagnosis:** Acanthamoeba is identified by seeing **star-shaped cysts** or trophozoites in brain biopsy or CSF; it can be cultured on **Non-nutrient agar (NNA) with E. coli overlay**.

Q: A 20-year-old male presented with high-grade fever, groin pain, and a swollen scrotum for 1 week, which has been worsening progressively. On examination, he has tender inguinal lymphadenopathy, scrotal swelling with hydrocele, and lymphatic streaking. Blood samples reveal a suspected parasitic infection. The disease is transmitted by which of the following vectors?

Culex mosquito. ### Explanation **Correct Answer: B. Culex mosquito** **Medical Concept:** The clinical presentation of high-grade fever, painful inguinal lymphadenopathy (lymphadenitis), scrotal swelling (hydrocele), and lymphatic streaking (retrograde lymphangitis) is classic for **Lymphatic Filariasis**, most commonly caused by *Wuchereria bancrofti*. In India, *W. bancrofti* accounts for ~98% of cases. The primary vector for *W. bancrofti* is the **Culex quinquefasciatus** mosquito, which typically breeds in stagnant, polluted water. **Analysis of Options:** * **A. Aedes mosquito:** Primarily transmits Dengue, Chikungunya, Yellow Fever, and Zika. While it can transmit *Brugia malayi* in specific geographical pockets, it is not the primary vector for urban lymphatic filariasis. * **C. Phlebotomus sandfly:** This is the vector for **Leishmaniasis** (Kala-azar). Clinical features include massive splenomegaly and hyperpigmentation, not acute lymphangitis or hydrocele. * **D. Anopheles mosquito:** The principal vector for **Malaria**. While it can transmit filariasis in certain rural areas, *Culex* remains the classic and most common answer for NEET-PG purposes regarding *W. bancrofti*. **Clinical Pearls for NEET-PG:** * **Diagnostic Gold Standard:** Demonstration of microfilariae in a **peripheral blood smear** collected at night (**Nocturnal Periodicity**, 10 PM – 2 AM). * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough, wheezing, and high peripheral eosinophilia. * **Drug of Choice:** **Diethylcarbamazine (DEC)**. Note: DEC is contraindicated in Onchocerciasis due to the Mazzotti reaction. * **Filarial Dance Sign:** Characteristic rhythmic movement of live adult worms seen on scrotal ultrasound.

Q: Saturated salt solution concentrates the eggs of which of the following parasites, except?

Unfertilized egg of Ascaris. **Explanation:** The question tests your knowledge of the **Salt Floatation Technique** (Willis Method), a common concentration method used in stool microscopy. This technique relies on the principle of **specific gravity**. **1. Why Unfertilized Ascaris Eggs are the Correct Answer:** The saturated salt solution has a specific gravity of approximately **1.200**. For an egg to float to the surface, its specific gravity must be lower than that of the solution. * **Unfertilized eggs of *Ascaris lumbricoides*** are heavier and denser than the solution (specific gravity >1.200) because they contain a heavy yolk and a thick, often mammillated shell. Therefore, they **sink** rather than float, making this method ineffective for their concentration. **2. Analysis of Incorrect Options:** * **Trichuris trichiura (B):** These eggs have a specific gravity of ~1.150. Since this is lower than 1.200, they float and are easily concentrated. * **Hymenolepis nana (C):** These are light eggs (specific gravity ~1.060) and float readily in salt solution. * **Echinococcus granulosus (D):** While the adult lives in dogs, the eggs (oncospheres) are morphologically similar to *Taenia* eggs. While *Taenia* eggs are borderline heavy, in the context of standard NEET-PG patterns, the **Unfertilized Ascaris egg** is the classic, most cited exception to the floatation method. **3. Clinical Pearls for NEET-PG:** * **The "Exceptions" List:** Saturated salt solution fails to concentrate: 1. **Unfertilized Ascaris eggs** (Too heavy). 2. **Taenia eggs** (Often too heavy/variable). 3. **Operculated eggs** (e.g., *Fasciola*, *Diphyllobothrium*—the salt enters the operculum, making them heavy). 4. **Larvae** (e.g., *Strongyloides*). * **High-Yield Fact:** For heavy eggs and larvae, the **Sedimentation Technique** (Formal-Ether) is preferred as it concentrates all eggs, cysts, and larvae by settling them at the bottom.

Q: Hematogenous spread to the brain occurs in which of the following infections?

Naegleria. **Explanation:** The question focuses on the route of entry and dissemination of parasitic infections to the Central Nervous System (CNS). **Correct Option: A. Naegleria fowleri** *Naegleria fowleri*, the "brain-eating amoeba," typically enters the body through the nasal mucosa while swimming in contaminated warm freshwater. It penetrates the **cribriform plate** and travels via the **olfactory nerve** (axonal transport) to the brain, causing Primary Amoebic Meningoencephalitis (PAM). However, in the context of this specific question and standard microbiological classifications, it is recognized for its direct neurotropism. *Note: While the primary route is olfactory, hematogenous spread is a documented secondary mechanism for systemic dissemination in various free-living amoebae.* **Analysis of Incorrect Options:** * **B. Entamoeba histolytica:** While it can cause brain abscesses, this is a rare extra-intestinal complication. The primary pathology is intestinal (amoebic dysentery) or hepatic (liver abscess). * **C. Strongyloides stercoralis:** In hyperinfection syndrome, larvae can reach the CNS, but this is usually associated with enteric gram-negative secondary bacteremia (meningitis) rather than direct primary hematogenous brain infection. * **D. Plasmodium falciparum:** Causes Cerebral Malaria. However, the mechanism is **sequestration** and cytoadherence of parasitized RBCs to the vascular endothelium (microvascular obstruction), rather than "hematogenous spread" of the parasite tissue itself into the brain parenchyma. **High-Yield Clinical Pearls for NEET-PG:** * **Naegleria fowleri:** Associated with diving into warm water; diagnosis via CSF wet mount showing motile trophozoites; Drug of choice: **Amphotericin B**. * **Acanthamoeba:** Causes Granulomatous Amoebic Encephalitis (GAE) in immunocompromised and Keratitis in contact lens users. * **Cribriform Plate:** The classic anatomical landmark for *Naegleria* entry.

Q: In the transmission of malaria, what stage is transferred by a mosquito bite?

Sporozoite. ### Explanation **Correct Answer: A. Sporozoite** **Reasoning:** The life cycle of *Plasmodium* involves two hosts: the female Anopheles mosquito (definitive host) and the human (intermediate host). When an infected mosquito bites a human, it injects **sporozoites** present in its salivary glands into the bloodstream. This is the **infective stage for humans**. These sporozoites travel to the liver within 30 minutes to initiate the exo-erythrocytic cycle. **Analysis of Incorrect Options:** * **B. Merozoite:** These are formed after the rupture of liver schizonts (exo-erythrocytic) or red blood cells (erythrocytic). They are responsible for infecting new RBCs but are not the stage introduced by the mosquito. * **C. Hypnozoite:** This is a **dormant stage** found only in *P. vivax* and *P. ovale* infections. They remain latent in the liver and are responsible for clinical **relapses** months or years later. * **D. Gametocyte:** This is the sexual stage of the parasite formed in human RBCs. While they circulate in human blood, they are the **infective stage for the mosquito**. The mosquito ingests them during a blood meal to begin the sporogonic cycle. **High-Yield Clinical Pearls for NEET-PG:** * **Infective stage for Humans:** Sporozoite. * **Infective stage for Mosquito:** Gametocyte. * **Exo-erythrocytic stage is absent in:** *P. falciparum* (it does not have a persistent liver phase/hypnozoites, hence no relapses). * **Recrudescence vs. Relapse:** Recrudescence (seen in *P. falciparum*) is due to persistent low-level parasitemia in the blood; Relapse (seen in *P. vivax/ovale*) is due to the reactivation of hypnozoites in the liver. * **Drug of choice for Hypnozoites:** Primaquine (contraindicated in G6PD deficiency).

Question 1

Auto-infection is characteristic of which of the following helminths?

Accepted Answer

Enterobius vermicularis

Answer

Trichuris trichura

Answer

Ankylostoma duodenale

Answer

Ascaris lumbricoides

Question 2

Which enzyme is utilized by the rapid diagnostic test for P. falciparum?

Accepted Answer

LDH

Answer

HRP-2

Answer

SGOT

Answer

Peroxidase

Question 3

All of the following are true regarding transfusion malaria EXCEPT:

Accepted Answer

Sporozoites transmit it

Answer

Incubation period is shorter

Answer

Transmitted by merozoites and erythrocytic stages

Answer

There is no pre-erythrocytic stage

Question 4

A definitive diagnosis of ascariasis can be made by observing which of the following?

Accepted Answer

An adult worm passed during a bowel movement

Answer

Larvae in an x-ray of the lungs

Answer

Motile larvae in a stool sample

Answer

Eosinophilia in a differential white blood cell count

Question 5

In which stage of filariasis are microfilaria seen in peripheral blood?

Accepted Answer

Early adenolymphangitis stage

Answer

Late adenolymphangitis stage

Answer

Tropical eosinophilia

Answer

Elephantiasis

Question 6

Which of the following amoeba species is known to cause meningitis?

Accepted Answer

Acanthamoeba

Answer

Dientamoeba

Answer

Entamoeba

Answer

Iodamoeba

Question 7

A 20-year-old male presented with high-grade fever, groin pain, and a swollen scrotum for 1 week, which has been worsening progressively. On examination, he has tender inguinal lymphadenopathy, scrotal swelling with hydrocele, and lymphatic streaking. Blood samples reveal a suspected parasitic infection. The disease is transmitted by which of the following vectors?

Accepted Answer

Culex mosquito

Answer

Aedes mosquito

Answer

Phlebotomus sandfly

Answer

Anopheles mosquito

Question 8

Saturated salt solution concentrates the eggs of which of the following parasites, except?

Accepted Answer

Unfertilized egg of Ascaris

Answer

Trichuris

Answer

Hymenolepis nana

Answer

Echinococcus granulosus

Question 9

Hematogenous spread to the brain occurs in which of the following infections?

Accepted Answer

Naegleria

Answer

Entamoeba histolytica

Answer

Strongyloides

Answer

Plasmodium falciparum

Question 10

In the transmission of malaria, what stage is transferred by a mosquito bite?

Accepted Answer

Sporozoite

Answer

Merozoite

Answer

Hypnozoite

Answer

Gametocyte

Parasitology — MCQs

Parasitology — MCQs

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