Parasitology Practice Questions

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).

Q: Which organism causes biliary duct obstruction?

Clonorchis sinensis. **Explanation:** **Clonorchis sinensis** (the Chinese Liver Fluke) is the correct answer because its primary habitat in the human body is the **biliary passages**. After ingestion of undercooked freshwater fish containing metacercariae, the larvae migrate to the distal bile ducts. Chronic infection leads to mechanical obstruction, inflammatory hyperplasia of the biliary epithelium, and periductal fibrosis. This can manifest clinically as biliary colic, jaundice, and cholangitis. **Analysis of Incorrect Options:** * **Ankylostoma duodenale (Hookworm):** Resides in the small intestine (jejunum) and attaches to the mucosa to suck blood, primarily causing iron-deficiency anemia, not biliary obstruction. * **Strongyloides stercoralis:** Primarily inhabits the mucosal glands of the duodenum and upper jejunum. It is known for its autoinfection cycle and hyperinfection syndrome in immunocompromised patients. * **Enterobius vermicularis (Pinworm):** Lives in the cecum and appendix. Its most common clinical presentation is perianal pruritus (itching) due to nocturnal egg deposition. **High-Yield Clinical Pearls for NEET-PG:** * **Carcinogenesis:** Chronic *Clonorchis sinensis* infection is a major risk factor for **Cholangiocarcinoma** (bile duct cancer). It is classified as a Group 1 carcinogen by the IARC. * **Intermediate Hosts:** 1st host: Snail (Parafossarulus); 2nd host: Cyprinidae family fish. * **Diagnosis:** Identification of characteristic "operculated eggs with a small knob" in stool or biliary aspirate. * **Treatment:** Praziquantel is the drug of choice. * **Other Biliary Flukes:** *Opisthorchis viverrini* and *Fasciola hepatica* can also cause similar biliary pathology.

Q: Nocturnal pruritus ani is characteristic of which of the following?

Enterobius. **Explanation:** **Enterobius vermicularis** (Pinworm or Seatworm) is the correct answer because of its unique life cycle. Unlike most intestinal nematodes, the gravid female Enterobius migrates out of the anus, typically at night (**nocturnal migration**), to deposit eggs on the perianal and perineal skin. The movement of the worm and the sticky substance used to adhere the eggs cause intense local irritation, leading to **nocturnal pruritus ani** (perianal itching). This often results in sleep disturbance and irritability in children. **Analysis of Incorrect Options:** * **Ascaris lumbricoides:** Primarily causes Loeffler’s syndrome (pulmonary phase) and intestinal obstruction. It does not migrate to the perianal region. * **Trichuris trichiura (Whipworm):** Associated with mucosal damage in the large intestine. Heavy infections typically lead to chronic diarrhea and **rectal prolapse**, but not perianal itching. * **Ancylostoma duodenale (Hookworm):** Known for causing iron deficiency anemia due to blood-sucking and "ground itch" at the site of larval skin penetration (usually the feet). **High-Yield Clinical Pearls for NEET-PG:** * **Diagnosis:** The investigation of choice is the **NIH Swab** or **Scotch Tape Test** (Cellophane tape test) performed early in the morning before bathing. Eggs are rarely found in routine stool samples. * **Morphology:** Eggs are characteristic **Planoconvex** (D-shaped). * **Transmission:** Autoinfection is common due to the finger-to-mouth transfer of eggs following scratching (fecal-oral). * **Treatment:** **Albendazole** or Mebendazole is used. It is crucial to treat the **entire family** simultaneously to prevent reinfection.

Question 1

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 2

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 3

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

Accepted Answer

Acanthamoeba

Answer

Dientamoeba

Answer

Entamoeba

Answer

Iodamoeba

Question 4

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 5

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 6

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

Accepted Answer

Naegleria

Answer

Entamoeba histolytica

Answer

Strongyloides

Answer

Plasmodium falciparum

Question 7

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

Accepted Answer

Sporozoite

Answer

Merozoite

Answer

Hypnozoite

Answer

Gametocyte

Question 8

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

Question 9

Which organism causes biliary duct obstruction?

Accepted Answer

Clonorchis sinensis

Answer

Ankylostoma duodenale

Answer

Strongyloides stercales

Answer

Enterobius vermicularis

Question 10

Nocturnal pruritus ani is characteristic of which of the following?

Accepted Answer

Enterobius

Answer

Ascaris

Answer

Trichuris

Answer

Ancylostoma

Parasitology — MCQs

Parasitology — MCQs

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