Parasitology Practice Questions

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: 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: 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: 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

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

Accepted Answer

LDH

Answer

HRP-2

Answer

SGOT

Answer

Peroxidase

Question 2

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 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

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 5

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

Accepted Answer

Acanthamoeba

Answer

Dientamoeba

Answer

Entamoeba

Answer

Iodamoeba

Question 6

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 7

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 8

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

Accepted Answer

Naegleria

Answer

Entamoeba histolytica

Answer

Strongyloides

Answer

Plasmodium falciparum

Question 9

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

Accepted Answer

Sporozoite

Answer

Merozoite

Answer

Hypnozoite

Answer

Gametocyte

Question 10

A patient complains of diarrhea. Stool examination shows ova. Which of the following cannot be the cause?

Accepted Answer

Opisthorchis viverni

Answer

Cryptosporidium

Answer

Isospora

Answer

E. histolytica

Parasitology — MCQs

Parasitology — MCQs

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