Parasitology Practice Questions

Q: A farmer's wife develops abdominal pain and diarrhea, followed several days later by fever, periorbital edema, eosinophilia, and myalgia. She does not remember eating anything unusual recently but notes that she makes her own pork sausage. Which of the following diagnostic techniques would be most helpful for this patient?

Muscle biopsy. ### Explanation The clinical presentation of abdominal pain followed by the triad of **periorbital edema, myalgia, and significant eosinophilia** in a patient consuming homemade pork sausage is classic for **Trichinellosis**, caused by the nematode *Trichinella spiralis*. **Why Muscle Biopsy is Correct:** The life cycle of *Trichinella* involves the ingestion of undercooked meat containing encysted larvae. After maturing in the small intestine (enteral phase), the female releases newborn larvae that migrate via the bloodstream to highly oxygenated skeletal muscles (parenteral phase). Here, they encyst within "nurse cells." A **muscle biopsy** (typically from the deltoid or gastrocnemius) performed 2–4 weeks after infection is the definitive diagnostic test to visualize these **encysted coiled larvae**. **Why Other Options are Incorrect:** * **Stool for ova and parasites:** Unlike most intestinal helminths, *Trichinella* eggs hatch within the female worm, and adults are rarely shed in feces. Therefore, stool examination is almost always negative and unreliable. * **Scotch tape test:** This is the diagnostic gold standard for *Enterobius vermicularis* (pinworm) to detect eggs deposited on the perianal skin. * **Gastric biopsy:** The parasite resides in the small intestine during the early phase and the muscles during the late phase; it does not involve the gastric mucosa. **High-Yield NEET-PG Pearls:** * **Source:** Undercooked pork (domestic cycle) or wild game like bear/boar (sylvatic cycle). * **Key Lab Finding:** Marked **Eosinophilia** (often >20%) and elevated **Creatine Kinase (CK)** due to muscle inflammation. * **Splinter hemorrhages:** Often seen under the fingernails alongside periorbital edema. * **Treatment:** Albendazole or Mebendazole (effective against intestinal adults); corticosteroids are added for severe systemic/myocardial symptoms.

Q: A 25-year-old patient presented with signs of meningoencephalitis following swimming in a nearby local pond one week back. The CSF on wet mount microscopy revealed motile unicellular microorganisms. What is the most likely organism?

Naegleria fowleri. ### **Explanation** **Correct Option: A. *Naegleria fowleri*** The clinical presentation describes a classic case of **Primary Amoebic Meningoencephalitis (PAM)**. *Naegleria fowleri* is a free-living thermophilic amoeba found in warm freshwater bodies (ponds, lakes). * **Mechanism:** The organism enters the nasal cavity during swimming, penetrates the **cribriform plate**, and migrates via the olfactory nerves to the brain. * **Diagnosis:** The presence of **motile trophozoites** (showing eruptive pseudopodia) in a wet mount of fresh CSF is the gold standard for rapid diagnosis. **Why other options are incorrect:** * **B. *Entamoeba histolytica*:** Primarily causes intestinal amoebiasis and liver abscesses. While it can rarely cause brain abscesses, it does not present as acute meningoencephalitis following swimming. * **C. *Giardia lamblia*:** An intestinal flagellate causing malabsorption and diarrhea; it has no CNS involvement. * **D. *Trypanosoma* species:** *T. brucei* causes African Sleeping Sickness, which is a chronic CNS infection transmitted by the Tsetse fly, not via water exposure. --- ### **High-Yield Clinical Pearls for NEET-PG** * **Drug of Choice:** **Amphotericin B** (often combined with Rifampicin or Miltefosine), though the prognosis remains extremely poor (mortality >95%). * **Differentiating Feature:** Unlike *Acanthamoeba* (which causes Granulomatous Amoebic Encephalitis in immunocompromised hosts), *Naegleria* causes **acute** infection in **previously healthy** individuals. * **Culture:** Can be grown on **Non-nutrient agar (NNA)** seeded with *E. coli*. * **CSF Findings:** Resembles pyogenic meningitis (high neutrophils, low sugar, high protein), but the presence of motile amoebae distinguishes it.

Q: Which tissue is most commonly affected in cysticercosis?

Muscle. **Explanation:** Cysticercosis is caused by the larval stage (*Cysticercus cellulosae*) of the pork tapeworm, **Taenia solium**. Humans become accidental intermediate hosts by ingesting eggs through contaminated food or water. **1. Why Muscle is Correct:** While Neurocysticercosis (NCC) is the most clinically significant and symptomatic presentation, **subcutaneous tissue and skeletal muscles** are statistically the **most common** sites of larval lodgment. In many cases, muscular involvement remains asymptomatic or presents as small, palpable, painless nodules, which is why it is often underdiagnosed compared to neurological involvement. **2. Analysis of Incorrect Options:** * **Brain (Option A):** This is the most common site for **symptomatic** cysticercosis and the leading cause of adult-onset seizures worldwide. However, in terms of absolute frequency of larval distribution in the body, it ranks second to muscle/subcutaneous tissue. * **Eye (Option B):** Ocular cysticercosis occurs in about 1–3% of cases. It can involve the subretinal space or vitreous, potentially causing blindness, but it is far less common than muscular or neural involvement. * **Liver (Option C):** The liver is the primary site for **Hydatid disease** (*Echinococcus granulosus*), not cysticercosis. *T. solium* larvae rarely involve the hepatic parenchyma. **High-Yield NEET-PG Pearls:** * **Definitive Host:** Human (harbors adult worm). * **Intermediate Host:** Pig (normal); Human (accidental). * **Mode of Infection for Cysticercosis:** Ingestion of eggs (fecal-oral) or autoinfection. (Note: Ingesting undercooked pork leads to intestinal Taeniasis, not cysticercosis). * **Diagnosis:** MRI is the gold standard for NCC (shows "scolex within a cyst"). * **Treatment:** Albendazole is the drug of choice (combined with steroids to prevent inflammatory response to dying larvae).

Q: What is the gold standard for the diagnosis of echinococcal cyst?

ELISA. **Explanation:** The diagnosis of **Echinococcal cyst (Hydatid disease)**, caused primarily by *Echinococcus granulosus*, relies on a combination of serology and imaging. **Why ELISA is the Correct Answer:** In the context of establishing a definitive diagnosis, **ELISA (Enzyme-Linked Immunosorbent Assay)** for IgG antibodies is considered the **gold standard** (specifically the screening test of choice with high sensitivity). While imaging identifies the lesion, serological confirmation is required to differentiate it from other cystic lesions (like simple cysts or abscesses) and to confirm the parasitic etiology. A positive ELISA is often followed by Western Blot for 100% specificity. **Analysis of Incorrect Options:** * **USG (Ultrasonography):** This is the **investigation of choice (IOC)** for screening and staging (Gharbi/WHO classification). It is excellent for visualizing daughter cysts and "water lily" signs but cannot provide a definitive serological diagnosis. * **CT Scan:** This is the best modality for detecting **wall calcification** and evaluating complications (rupture/infection) or cysts in extrahepatic locations. It is more sensitive than USG for calcification but is not the diagnostic gold standard. * **X-ray:** This may show incidental curvilinear calcification (eggshell calcification) in the right upper quadrant, but it lacks the sensitivity and specificity for a formal diagnosis. **Clinical Pearls for NEET-PG:** * **Pathognomonic Sign:** "Water lily sign" (detached endocyst membrane) seen on USG/CT. * **Treatment of Choice:** Surgical excision (modified PAIR technique or cystectomy) combined with **Albendazole**. * **Caution:** Diagnostic aspiration (FNA) is generally **contraindicated** due to the risk of anaphylactic shock from spillage of cyst fluid. * **Calcification:** A completely calcified cyst usually indicates a dead/inactive parasite.

Q: Black water fever is caused by?

P. falciparum. **Explanation:** **Blackwater Fever** is a severe and life-threatening complication of malaria specifically caused by **Plasmodium falciparum**. **Why P. falciparum is correct:** The condition is characterized by massive **intravascular hemolysis** (destruction of red blood cells within the blood vessels). This leads to severe hemoglobinemia and subsequent **hemoglobinuria**, which turns the urine a dark red, brown, or black color (hence the name "Blackwater"). The underlying mechanism involves a Type II hypersensitivity-like reaction, often triggered in patients with repeated infections or those treated irregularly with Quinine. The massive release of hemoglobin can lead to acute tubular necrosis and **acute renal failure**, which is the primary cause of mortality. **Why other options are incorrect:** * **P. vivax:** While it causes significant morbidity and "Benign Tertian Malaria," it rarely causes the massive intravascular hemolysis required to produce blackwater fever. * **Kala-azar / Leishmaniasis:** These are caused by *Leishmania donovani*. While they cause pancytopenia and massive splenomegaly, they do not cause acute intravascular hemolysis or hemoglobinuria. **NEET-PG High-Yield Pearls:** * **Key Triad:** Hemolysis, hemoglobinuria, and acute renal failure. * **Parasite Load:** *P. falciparum* is the most severe because it infects RBCs of all ages (unlike *P. vivax* which prefers reticulocytes). * **Sequestration:** *P. falciparum* causes RBCs to develop "knobs" (PfEMP-1), leading to cytoadherence and microvascular occlusion (Cerebral Malaria). * **Drug Association:** Historically associated with **Quinine** therapy.

Q: What is the infective form of Plasmodium falciparum in the mosquito?

Gametocytes. **Explanation:** The life cycle of *Plasmodium falciparum* involves two hosts: the human (intermediate host) and the female *Anopheles* mosquito (definitive host). **Why Gametocytes are correct:** For the mosquito to become infected, it must ingest the sexual stages of the parasite present in human peripheral blood. These are the **Gametocytes** (male microgametocytes and female macrogametocytes). Once inside the mosquito's midgut, these gametocytes undergo fertilization to begin the sporogonic cycle, eventually leading to the production of sporozoites. Therefore, gametocytes are the **infective form for the mosquito**. **Why other options are incorrect:** * **Sporozoites (Option B):** These are the **infective form for humans**. They are inoculated into the human bloodstream via the mosquito's saliva during a blood meal. * **Merozoites (Option A):** These are released from hepatic cells (exo-erythrocytic stage) or red blood cells (erythrocytic stage). They infect new RBCs but are digested if ingested by a mosquito. * **Trophozoites (Option D):** This is the metabolically active, feeding stage within the human RBC (e.g., "ring forms"). Like merozoites, they do not survive the mosquito's digestive tract. **High-Yield NEET-PG Pearls:** * **Definitive Host:** Female *Anopheles* mosquito (where the sexual cycle occurs). * **Intermediate Host:** Humans (where the asexual cycle/schizogony occurs). * **P. falciparum Gametocytes:** Characteristically **crescent or banana-shaped**, appearing in peripheral blood 7–10 days after the initial infection. * **Primaquine:** The drug of choice for its gametocidal action against *P. falciparum*, used to prevent the transmission of malaria back to the mosquito.

Q: Which of the following diseases are transmitted by the sandfly?

Kala-azar. **Explanation:** The sandfly (genus *Phlebotomus* in the Old World and *Lutzomyia* in the New World) is a significant medical vector. The correct answer is **Kala-azar** (Visceral Leishmaniasis), caused by *Leishmania donovani*. The sandfly transmits the parasite in its **promastigote** stage through a bite, which then transforms into the **amastigote** stage within the host's macrophages. **Analysis of Options:** * **A. Kala-azar (Correct):** Transmitted by *Phlebotomus argentipes*. It is characterized by the classic triad of fever, hepatosplenomegaly, and pancytopenia. * **B. Oriental Sore:** While also transmitted by the sandfly (*P. papatasi*), it refers to **Cutaneous Leishmaniasis**. In many competitive exams, if "Kala-azar" is an option, it is prioritized as the primary disease associated with sandflies in the Indian subcontinent. * **C. Relapsing Fever:** Epidemic relapsing fever is transmitted by the **body louse** (*Pediculus humanus corporis*), while endemic relapsing fever is transmitted by **soft ticks** (*Ornithodoros*). * **D. Oroya Fever:** This is the acute febrile phase of **Carrion’s disease** (caused by *Bartonella bacilliformis*). It is indeed transmitted by the sandfly (*Lutzomyia*), but it is geographically restricted to the Andes region of South America, making Kala-azar the more globally and locally relevant answer for NEET-PG. **High-Yield Clinical Pearls:** * **Sandfly-borne diseases mnemonic (6 O's):** **O**roya fever, **O**riental sore, **O**ld world Leishmaniasis, **O**ndansetron (not related, but helps memory), **O**ther Leishmaniasis, and **O**ropouche virus. * **Sandfly characteristics:** They are small (1/4 size of a mosquito), crawl rather than fly (short hops), and are nocturnal. * **Drug of Choice for Kala-azar:** Liposomal Amphotericin B is currently the first-line treatment.

Question 1

A farmer's wife develops abdominal pain and diarrhea, followed several days later by fever, periorbital edema, eosinophilia, and myalgia. She does not remember eating anything unusual recently but notes that she makes her own pork sausage. Which of the following diagnostic techniques would be most helpful for this patient?

Accepted Answer

Muscle biopsy

Answer

Gastric biopsy

Answer

Scotch tape test

Answer

Stool for ova and parasites

Question 2

A 25-year-old patient presented with signs of meningoencephalitis following swimming in a nearby local pond one week back. The CSF on wet mount microscopy revealed motile unicellular microorganisms. What is the most likely organism?

Accepted Answer

Naegleria fowleri

Answer

Entamoeba histolytica

Answer

Giardia lamblia

Answer

Trypanosoma species

Question 3

Which tissue is most commonly affected in cysticercosis?

Accepted Answer

Muscle

Answer

Brain

Answer

Eye

Answer

Liver

Question 4

A 28-year-old man presents with vague muscle pain involving his right arm that developed several weeks after eating undercooked meat. A biopsy from the affected muscle reveals encysted forms of Trichinella spiralis. What type of white blood cell is most likely to be increased in numbers in the peripheral blood of this individual?

Accepted Answer

Eosinophil

Answer

Basophil

Answer

Macrophage

Answer

Neutrophil

Question 5

Dracunculosis infection occurs through which mode of transmission?

Accepted Answer

Ingestion of water containing cyclops infected with the parasite

Answer

Ingestion of water containing the parasite directly

Answer

Ingestion of contaminated fish

Answer

Penetration of skin by the parasite

Question 6

Sputum examination is not useful in the diagnosis of which of the following parasitic infections?

Accepted Answer

Trichuris trichura

Answer

Ancylostoma duodenale

Answer

Paragonimiasis

Answer

Strongyloides stercoralis

Question 7

What is the gold standard for the diagnosis of echinococcal cyst?

Accepted Answer

ELISA

Answer

X-ray

Answer

CT scan

Answer

USG

Question 8

Black water fever is caused by?

Accepted Answer

P. falciparum

Answer

Kala azar

Answer

P. vivax

Answer

Leishmaniasis

Question 9

What is the infective form of Plasmodium falciparum in the mosquito?

Accepted Answer

Gametocytes

Answer

Merozoites

Answer

Sporozoites

Answer

Trophozoites

Question 10

Which of the following diseases are transmitted by the sandfly?

Accepted Answer

Kala-azar

Answer

Oriental sore

Answer

Relapsing fever

Answer

Oraya fever

Parasitology — MCQs

Parasitology — MCQs

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