Parasitology Practice Questions

Q: The most sensitive among the following tests for the diagnosis of malaria is?

Quantitative buffy coat test. The diagnosis of malaria relies on the detection of Plasmodium parasites or their components in the blood. The **Quantitative Buffy Coat (QBC)** test is the most sensitive method among the options provided. [1] **1. Why QBC is the correct answer:** The QBC technique involves staining a specialized capillary tube with acridine orange and centrifuging it. [1] Centrifugation concentrates the parasites (which contain DNA) into a small area just below the white blood cell layer (the buffy coat). Because the parasites are **concentrated** and fluoresce under a microscope, QBC can detect as few as **5 parasites per microliter** of blood, making it significantly more sensitive than standard microscopy. **2. Why other options are incorrect:** * **Thin peripheral blood smear:** While excellent for **speciation** (identifying the species) and quantifying parasite density, it is less sensitive than thick smears or QBC because it uses a smaller volume of blood. * **PfHRP2 (Rapid Diagnostic Test):** This detects the Histidine-Rich Protein 2 of *P. falciparum*. While fast, it can yield false negatives in low parasitemia or "prozone effect" scenarios and false positives due to persistent antigens after treatment. [1] * **Pan plasmodial LDH:** This enzyme-based RDT is less sensitive than QBC and HRP2, particularly at low parasite levels, and is primarily used to monitor treatment response as LDH is only produced by live parasites. [1] **Clinical Pearls for NEET-PG:** * **Gold Standard:** Light microscopy (Thick and Thin smears) remains the "Gold Standard" for routine diagnosis. * **Thick Smear:** Used for **screening** (more sensitive than thin smear). * **Thin Smear:** Used for **species identification**. * **Most Sensitive Overall:** PCR (Polymerase Chain Reaction) is the most sensitive test available, but among the clinical/microscopic options listed, QBC is superior. [1] [2]

Q: How is primary amoebic meningoencephalitis most likely acquired?

Diving or swimming in contaminated water. **Explanation:** **Primary Amoebic Meningoencephalitis (PAM)** is caused by ***Naegleria fowleri***, often referred to as the "brain-eating amoeba." This free-living amoeba thrives in warm, stagnant freshwater (lakes, ponds, and poorly chlorinated swimming pools). 1. **Why Option A is correct:** The infection is acquired when water containing the amoebae is forcefully pushed into the nasal cavity, typically during **diving or swimming**. The amoebae penetrate the **nasal mucosa**, cross the **cribriform plate**, and migrate along the **olfactory nerves** to reach the brain. This leads to rapid, fulminant destruction of brain tissue and meningeal inflammation. 2. **Why other options are incorrect:** * **Option B:** IV drug abuse is associated with infections like HIV, Hepatitis B/C, or fungal endocarditis, but not PAM. * **Option C:** Using human excrement (night soil) as fertilizer is a common transmission route for soil-transmitted helminths (e.g., *Ascaris*) or feco-oral protozoa (e.g., *Entamoeba histolytica*), which cause intestinal or liver abscesses, not PAM. * **Option D:** Raw fish/seafood consumption is linked to parasites like *Diphyllobothrium latum* (fish tapeworm) or *Anisakis*, not *Naegleria*. **High-Yield Clinical Pearls for NEET-PG:** * **Pathogen:** *Naegleria fowleri* is a thermophilic amoeba (grows at temperatures up to 45°C). * **Diagnosis:** Look for **motile trophozoites** in a fresh wet mount of **CSF**. * **CSF Findings:** Resembles bacterial meningitis (high neutrophils, low glucose, high protein) but with RBCs (hemorrhagic). * **Treatment:** Drug of choice is **Amphotericin B**. * **Note:** Do not confuse PAM with **Granulomatous Amoebic Encephalitis (GAE)**, which is caused by *Acanthamoeba* or *Balamuthia* and typically occurs in immunocompromised patients via skin or respiratory routes.

Q: Which nematode resides in the caecum and appendix?

Enterobius vermicularis. **Explanation:** The correct answer is **Enterobius vermicularis** (Pinworm or Seatworm). **1. Why Enterobius vermicularis is correct:** The adult worms of *Enterobius vermicularis* primarily inhabit the **caecum, appendix, and adjacent portions of the ascending colon**. They attach to the mucosa using their mouth parts. A unique feature of their life cycle is that the gravid females migrate nocturnally through the anal canal to deposit eggs on the perianal skin, leading to the classic symptom of **pruritus ani**. **2. Why the other options are incorrect:** * **Ascaris lumbricoides (Roundworm):** The adult worms reside in the **lumen of the small intestine** (jejunum). While they can occasionally migrate into the appendix causing appendicitis, their primary habitat is not the caecum. * **Mansonella ozzardi:** This is a filarial nematode. The adult worms reside in the **mesentery, subperitoneal tissues, or thoracic cavity**, while the microfilariae circulate in the blood. They do not inhabit the intestinal lumen. **3. NEET-PG Clinical Pearls:** * **Diagnosis:** The "Gold Standard" is the **NIH Swab** or **Scotch Tape technique** performed early in the morning. Stool examination for eggs is usually negative (only 5% sensitivity) because eggs are laid on perianal skin, not in feces. * **Transmission:** Autoinfection and retroinfection are common. It is often a "familial infection." * **Drug of Choice:** Albendazole or Mebendazole (single dose, repeated after 2 weeks to kill newly hatched larvae). * **Ectopic sites:** In females, the worm can migrate into the vulva and vagina, causing vulvovaginitis or salpingitis.

Q: What is the natural habitat of Schistosoma (blood flukes)?

All of the above. **Explanation:** The correct answer is **D. All of the above**. Schistosomes, unlike other trematodes (flukes), are unique because they reside in the **venous system** of their definitive host (humans) rather than the intestine or liver. They are dioecious (separate sexes) and live in permanent copulation within the veins. 1. **Why the answer is correct:** The term "Schistosoma" refers to a genus that includes several species with specific anatomical preferences. * ***S. haematobium*** primarily inhabits the **vesical and pelvic venous plexuses** (surrounding the urinary bladder). * ***S. mansoni*** and ***S. japonicum*** reside in the **portal venous system** and mesenteric veins. Since the question asks for the habitat of "Schistosoma" (the genus) generally, all listed venous sites are correct. 2. **Analysis of Options:** * **Option A & C:** These are the specific habitats for *S. haematobium*. Eggs are deposited in the bladder wall, leading to terminal hematuria. * **Option B:** The portal vein is the site where schistosomes mature, and the pelvic/mesenteric veins are where they reside as adults. **High-Yield NEET-PG Pearls:** * **Infective stage:** Cercaria (enters via skin penetration, often during swimming). * **Diagnostic stage:** Non-operculated eggs with characteristic spines (*S. haematobium*: Terminal spine; *S. mansoni*: Lateral spine; *S. japonicum*: Rudimentary spine). * **Intermediate host:** Freshwater snails (*Biomphalaria*, *Bulinus*, *Oncomelania*). * **Clinical Association:** *S. haematobium* is a known risk factor for **Squamous Cell Carcinoma of the bladder**. * **Treatment of choice:** Praziquantel.

Q: A patient from a tribal area of Jharkhand presents with fever for the last 3 days. Peripheral blood is collected and stained with Giemsa. A diagnosis of malaria is made. The smear is shown in the figure. What is the likely causative species?

Plasmodium falciparum. ***Plasmodium falciparum*** - **Multiple ring forms** per RBC and **double chromatin dots** are characteristic features seen on Giemsa-stained smears, along with **appliqué position** (rings attached to RBC membrane). - **No RBC enlargement** is observed, and **crescent-shaped gametocytes** are pathognomonic when present; high prevalence in **tribal areas of Jharkhand**. *Plasmodium vivax* - Shows **enlarged RBCs** with **Schüffner's dots** and typically **single ring forms** per infected cell. - **Oval-shaped gametocytes** and **amoeboid trophozoites** are characteristic, unlike the multiple rings seen in P. falciparum. *Plasmodium malariae* - Produces **band-form trophozoites** that span across the RBC diameter and **rosette-pattern schizonts**. - **72-hour fever cycle** and **no RBC enlargement**, but lacks the multiple ring forms typical of P. falciparum. *Plasmodium ovale* - Shows **oval-shaped RBCs** with **fimbriated edges** and **Schüffner's dots** similar to P. vivax. - **Single ring forms** per RBC and **compact trophozoites**, not the multiple rings characteristic of P. falciparum infections.

Q: Diphyllobothrium latum is transmitted by which of the following modes?

Ingestion of plerocercoids through raw or undercooked fish. **Explanation:** *Diphyllobothrium latum* (the Fish Tapeworm) is the largest parasite infecting humans. Its complex life cycle involves two intermediate hosts: first, a **copepod** (crustacean), and second, a **freshwater fish**. **1. Why Option C is Correct:** The infective stage for humans is the **Plerocercoid larva** (also known as the sparganum). After a fish consumes an infected copepod, the larvae migrate into the fish's muscle. Humans acquire the infection by **ingesting raw or undercooked fish** containing these plerocercoids. Once inside the human intestine, they develop into adult worms. **2. Why the Other Options are Incorrect:** * **Options A & B:** **Cercariae** are the infective stages for Trematodes (Flukes), such as *Schistosoma*, not Cestodes (Tapeworms). In the *D. latum* cycle, the stage found in copepods is the *procercoid* larva, not cercariae. * **Option D:** **Metacercariae** are the infective stages for hermaphroditic flukes (e.g., *Fasciola hepatica*, *Clonorchis sinensis*). While copepods are involved in the life cycle of *D. latum*, they harbor *procercoids*, not metacercariae. **Clinical Pearls for NEET-PG:** * **Vitamin B12 Deficiency:** *D. latum* competes with the host for Vitamin B12 absorption in the jejunum, leading to **Megaloblastic Anemia** and subacute combined degeneration of the spinal cord. * **Operculated Eggs:** It is the only human tapeworm that produces operculated eggs (similar to fluke eggs) and has a ciliated larval stage called **Coracidium**. * **Treatment:** Praziquantel is the drug of choice.

Q: What is the basis for the 'Dipstick Test' used for the rapid diagnosis of Plasmodium falciparum?

Histidine-rich protein. ### Explanation The correct answer is **D. Histidine-rich protein (HRP-2)**. **1. Why Histidine-rich protein is correct:** Rapid Diagnostic Tests (RDTs) for Malaria, often called the 'Dipstick Test', utilize immunochromatographic methods to detect specific circulating antigens. **Histidine-rich protein 2 (HRP-2)** is a water-soluble protein produced specifically by the asexual stages and young gametocytes of ***Plasmodium falciparum***. Because HRP-2 is secreted into the host’s bloodstream, it serves as a highly sensitive biomarker for diagnosing *P. falciparum* infections, even when parasite density is low. **2. Why the other options are incorrect:** * **Arginine, Serine, and Tyrosine-rich proteins:** While *Plasmodium* species do possess various proteins rich in these amino acids (e.g., Serine-repeat antigen), they are not utilized in commercial rapid diagnostic dipsticks. HRP-2 is uniquely targeted because of its high expression levels and specificity to the *falciparum* species. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Target Antigens:** * **HRP-2:** Specific for *P. falciparum* only. * **pLDH (Parasite Lactate Dehydrogenase):** Produced by all four species (*P. falciparum, P. vivax, P. ovale, P. malariae*). It indicates the presence of **viable** parasites. * **Persistence:** HRP-2 can persist in the blood for **2–4 weeks** even after successful treatment. Therefore, a positive dipstick test immediately after treatment may represent a "false positive" for active infection. * **Prozone Effect:** Very high parasitemia can sometimes lead to a false-negative result in RDTs due to the prozone phenomenon. * **Gold Standard:** Despite the convenience of RDTs, **Microscopy** (Peripheral Smear) remains the gold standard for malaria diagnosis.

Q: Which of the following is false about Echinococcus granulosus?

Hydatid fluid is secreted by the ectocyst. **Explanation:** The correct answer is **D**. In *Echinococcus granulosus* (Hydatid disease), the cyst wall consists of three layers. The **ectocyst** is the outermost, thick, fibrous layer formed by the **host’s inflammatory response**. It is not a part of the parasite itself and does not secrete fluid. The hydatid fluid is actually secreted by the **endocyst** (germinal layer), which is the innermost, metabolically active layer of the parasite. **Analysis of Options:** * **A. Man is the dead-end host:** True. Humans act as accidental intermediate hosts. Since the life cycle is broken (human-to-dog transmission does not occur), they are considered dead-end hosts. * **B. It causes hydatid disease:** True. *E. granulosus* is the causative agent of cystic echinococcosis, commonly known as hydatid disease, primarily affecting the liver and lungs. * **C. Casoni's test is sensitive:** True. This is an immediate hypersensitivity skin test. While it has high sensitivity (approx. 90%), it is rarely used today due to low specificity and the risk of anaphylaxis; it has been replaced by serology (ELISA) and imaging. **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Dog (adult worm lives in the intestine). * **Intermediate Host:** Sheep (natural) and Man (accidental). * **Infective Stage:** Embryonated eggs (found in dog feces). * **Hydatid Sand:** Consists of free scolices, daughter cysts, and hooklets found within the fluid. * **Water Lily Sign:** Seen on imaging when the endocyst ruptures and floats within the ectocyst. * **Treatment:** PAIR (Puncture, Aspiration, Injection, Re-aspiration) technique and Albendazole. Avoid cyst rupture to prevent life-threatening **anaphylactic shock**.

Question 1

The most sensitive among the following tests for the diagnosis of malaria is?

Accepted Answer

Quantitative buffy coat test

Answer

Thin peripheral blood smear

Answer

PfHRP2 antigen test

Answer

Pan plasmodial LDH test

Question 2

How is primary amoebic meningoencephalitis most likely acquired?

Accepted Answer

Diving or swimming in contaminated water

Answer

Intravenous drug abuse

Answer

Using human excrement as vegetable fertilizer

Answer

Eating raw fish or seafood

Question 3

Which nematode resides in the caecum and appendix?

Accepted Answer

Enterobius vermicularis

Answer

Ascaris lumbricoides

Answer

Mansonella ozzardi

Answer

All of these

Question 4

A man working in a construction company presented with watery, foul-smelling diarrhea since 3 weeks. There is no blood in the stools. If giardiasis is suspected, what is the best diagnostic method?

Accepted Answer

Presence of both cysts and trophozoites in stools

Answer

Complement fixation test (CFT)

Answer

Presence of cysts only

Answer

Haemagglutination

Question 5

Which parasite commonly causes pulmonary eosinophilia syndrome?

Accepted Answer

Strongyloides

Answer

Enterobiasis

Answer

Hookworm

Answer

Trichinella

Question 6

What is the natural habitat of Schistosoma (blood flukes)?

Accepted Answer

All of the above

Answer

Veins of the urinary bladder

Answer

Portal and pelvic veins

Answer

Vesical plexuses

Question 7

A patient from a tribal area of Jharkhand presents with fever for the last 3 days. Peripheral blood is collected and stained with Giemsa. A diagnosis of malaria is made. The smear is shown in the figure. What is the likely causative species?

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium vivax

Answer

Plasmodium malariae

Answer

Plasmodium ovale

Question 8

Diphyllobothrium latum is transmitted by which of the following modes?

Accepted Answer

Ingestion of plerocercoids through raw or undercooked fish

Answer

Ingestion of cercariae through copepods

Answer

Ingestion of cercariae through fish meal

Answer

Ingestion of metacercariae in copepods

Question 9

What is the basis for the 'Dipstick Test' used for the rapid diagnosis of Plasmodium falciparum?

Accepted Answer

Histidine-rich protein

Answer

Arginine-rich protein

Answer

Serine-rich protein

Answer

Tyrosine-rich protein

Question 10

Which of the following is false about Echinococcus granulosus?

Accepted Answer

Hydatid fluid is secreted by the ectocyst

Answer

Man is the dead-end host

Answer

It causes hydatid disease

Answer

Casoni's test is sensitive

Parasitology — MCQs

Parasitology — MCQs

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