Parasitology — MCQs

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?

Q659Easy

What is the infectious stage of Plasmodium?

Q660Medium

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?

Parasitology Indian Medical PG Practice Questions and MCQs

Question 651: Tick is involved in the transmission of all the following diseases except?

A. Tick typhus
B. Tularaemia
C. Lyme disease
D. Q fever (Correct Answer)

Explanation: **Explanation:** The correct answer is **Q fever**. While *Coxiella burnetii* (the causative agent of Q fever) can be found in ticks, human transmission occurs primarily through the **inhalation of contaminated aerosols** or dust from infected livestock (cattle, sheep, goats) [1], [2]. It is considered an occupational hazard for farmers and veterinarians. Unlike the other options, a tick bite is not the primary or common mode of transmission for Q fever [3]. **Analysis of other options:** * **Tick typhus:** Caused by *Rickettsia conorii* (Indian Tick Typhus), it is transmitted via the bite of hard ticks (*Rhipicephalus sanguineus*) [3]. * **Tularaemia:** Caused by *Francisella tularensis*, it is transmitted through various routes, including the bite of infected ticks (*Dermacentor* species), handling infected animal carcasses, or contaminated water. * **Lyme disease:** Caused by *Borrelia burgdorferi*, it is classically transmitted by the bite of *Ixodes* (hard) ticks. **High-Yield Clinical Pearls for NEET-PG:** 1. **Q Fever Unique Features:** It is the only Rickettsial disease that **does not present with a rash** and gives a **negative Weil-Felix reaction** [1]. 2. **Diagnosis:** The most common clinical presentation is an undifferentiated febrile illness, pneumonia, or hepatitis [1]. Chronic Q fever often manifests as culture-negative endocarditis [2]. 3. **Vector Mnemonic:** Remember "Ticks" for **L**yme, **E**hrlichiosis, **B**abesiosis, and **R**ickettsial diseases (except Epidemic/Endemic typhus) [3]. 4. **Infectivity:** *Coxiella burnetii* is highly infectious; a single organism can cause disease, making it a potential bioterrorism agent.

Question 652: Which of the following parasite infestations may be found in the extraocular eye muscles?

A. Ascariasis
B. Ankylostoma duodenale
C. Cysticercosis (Correct Answer)
D. Trypanosomiasis

Explanation: **Explanation:** **Cysticercosis** is caused by the larval stage (*Cysticercus cellulosae*) of the pork tapeworm, *Taenia solium*. While the central nervous system is the most common site (Neurocysticercosis), **Ocular Cysticercosis** occurs in about 13–46% of infected individuals. Within the eye, the parasite most frequently involves the subretinal space or the vitreous; however, **extraocular muscle involvement** (orbital cysticercosis) is a well-documented clinical entity. It typically presents with proptosis, ptosis, or restricted ocular motility, often mimicking an orbital mass or myositis. **Analysis of Incorrect Options:** * **Ascariasis (*Ascaris lumbricoides*):** These are intestinal nematodes. While larvae migrate through the lungs (Loeffler’s syndrome), they do not typically encyst in extraocular muscles. * **Ankylostoma duodenale (Hookworm):** These parasites primarily cause iron-deficiency anemia and cutaneous larva migrans. They do not have a predilection for ocular muscle tissue. * **Trypanosomiasis:** *T. cruzi* (Chagas disease) can cause unilateral palpebral edema (Romaña's sign), but this is an inflammatory response to the bite/feces near the eye, not an infestation of the extraocular muscles themselves. **High-Yield Clinical Pearls for NEET-PG:** * **Most common site for Ocular Cysticercosis:** Subretinal space. * **Most common extraocular muscle involved:** Superior rectus. * **Diagnosis:** B-scan Ultrasonography or MRI showing a cystic lesion with a high-amplitude "scolex" (the bright spot). * **Differential Diagnosis:** **Trichinellosis** (*Trichinella spiralis*) is another parasite famous for encysting in striated muscles, including extraocular muscles, often presenting with periorbital edema and myalgia.

Question 653: The enteric cycle of Toxoplasma gondii occurs in which host?

A. Rat
B. Cat (Correct Answer)
C. Cow
D. Sheep

Explanation: ### Explanation **Correct Answer: B. Cat** *Toxoplasma gondii* is an obligate intracellular protozoan with a complex life cycle involving two distinct phases: the **Enteric (Sexual) cycle** and the **Exo-enteric (Asexual) cycle**. 1. **Why Cat is Correct:** Members of the family **Felidae** (domestic cats and their relatives) are the **definitive hosts**. The enteric cycle occurs exclusively in the epithelial cells of the cat's small intestine. Here, the parasite undergoes gametogony and zygote formation, resulting in the production of **oocysts**, which are then excreted in the feces. This is the only stage where environmental contamination via oocysts occurs. 2. **Why Other Options are Incorrect:** * **A, C, and D (Rat, Cow, Sheep):** These are **intermediate hosts**. In these animals (and humans), only the **exo-enteric cycle** occurs. The parasite exists as rapidly multiplying **tachyzoites** (acute phase) or slow-growing **bradyzoites** within tissue cysts (chronic phase). They do not produce oocysts; therefore, the enteric cycle cannot take place in them. ### NEET-PG High-Yield Pearls: * **Definitive Host:** Cat (Sexual cycle). * **Intermediate Host:** Humans, mammals, and birds (Asexual cycle). * **Infective Stages:** 1. **Oocysts** (from cat feces). 2. **Bradyzoites** (in undercooked meat/tissue cysts). 3. **Tachyzoites** (transplacental transmission). * **Diagnosis:** Sabin-Feldman Dye Test (Gold Standard), though rarely used now; IgM/IgG ELISA is standard. * **Congenital Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Treatment of Choice:** Pyrimethamine + Sulfadiazine.

Question 654: Which of the following is used for the diagnosis of falciparum malaria?

A. HRP I
B. HRP II (Correct Answer)
C. HRP III
D. HRP IV

Explanation: **Explanation:** The diagnosis of *Plasmodium falciparum* malaria using Rapid Diagnostic Tests (RDTs) primarily relies on the detection of the **Histidine-Rich Protein II (HRP II)**. **Why HRP II is the Correct Answer:** HRP II is a water-soluble protein produced specifically by the asexual stages and young gametocytes of *Plasmodium falciparum*. It is secreted into the host’s bloodstream, making it an ideal biomarker for immunochromatographic tests (RDTs). Its high sensitivity and specificity for *P. falciparum* allow for rapid bedside diagnosis, even when microscopy is unavailable. **Analysis of Incorrect Options:** * **HRP I:** While *P. falciparum* produces other histidine-rich proteins like HRP I (Knob-associated HRP), it is not used in standard diagnostic kits as it is not as secreted or stable in the peripheral blood as HRP II. * **HRP III:** This protein shares structural similarities (epitopes) with HRP II. While some RDTs may show cross-reactivity with HRP III, it is not the primary target for diagnosis. Deletions in both *pfhrp2* and *pfhrp3* genes are a rising concern for "false negative" RDT results. * **HRP IV:** This is not a recognized diagnostic biomarker for malaria. **High-Yield Clinical Pearls for NEET-PG:** 1. **Other Biomarkers:** While HRP II is specific to *P. falciparum*, **pLDH (Parasite Lactate Dehydrogenase)** and **Aldolase** are used as "pan-malarial" markers to detect other species like *P. vivax*. 2. **Persistence:** HRP II can persist in the blood for **2–4 weeks** even after successful treatment. Therefore, a positive HRP II test does not always indicate an active, current infection in a recently treated patient. 3. **Prognosis:** The concentration of HRP II in the blood correlates with the total parasite biomass, often reflecting the severity of the disease.

Question 655: Which compound is used for the fixation of protozoa found in stool?

A. Phenol
B. Hypochlorite
C. Formalin (Correct Answer)
D. Alcohol

Explanation: **Explanation:** The preservation of stool samples is critical for the accurate diagnosis of parasitic infections, as trophozoites and cysts can degenerate rapidly after collection. **1. Why Formalin is the Correct Answer:** **Formalin (10% aqueous solution)** is the most widely used preservative for stool specimens. It is highly effective at preserving the morphology of **protozoan cysts** and helminth eggs/larvae for long periods. It is the gold standard for concentration techniques (like the Formalin-Ether sedimentation method) and is compatible with direct wet mounts and automated immunoassay kits. **2. Analysis of Incorrect Options:** * **Phenol:** While phenol has disinfectant properties, it is not used as a primary fixative for stool parasites because it can distort delicate cellular structures. * **Hypochlorite:** Sodium hypochlorite (bleach) is a powerful disinfectant used for surface decontamination. It is **contraindicated** for parasite preservation as it destroys the morphology of cysts and trophozoites, making microscopic identification impossible. * **Alcohol:** While 70% ethanol is used for preserving adult worms (helminths), it is not the primary choice for protozoa in stool. However, Polyvinyl Alcohol (PVA) is often used as a "glue" to attach stool to slides for permanent staining (like Trichrome), but the active fixative in that mixture is usually Schaudinn’s fluid (mercuric chloride). **Clinical Pearls for NEET-PG:** * **Two-Vial System:** Standard protocol often involves one vial of **10% Formalin** (for concentration/wet mounts) and one vial of **PVA** (for permanent staining). * **Trophozoite Preservation:** Formalin preserves cysts well, but for the fragile **trophozoite** stage, Schaudinn’s fixative or SAF (Sodium acetate-acetic acid-formalin) is preferred. * **MIF (Merthiolate-Iodine-Formalin):** A common field stain/fixative that both preserves and stains the specimen simultaneously.

Question 656: How many nuclei are present in the mature cyst of E. histolytica?

A. 1
B. 2
C. 4 (Correct Answer)
D. 8

Explanation: ### Explanation The life cycle of *Entamoeba histolytica* involves two stages: the **trophozoite** (motile, feeding stage) and the **cyst** (infective, resistant stage). **Why Option C is correct:** The process of encystation begins when a trophozoite undergoes dehydration in the colon. It first forms a **precyst**, which contains a single nucleus. This nucleus undergoes two successive mitotic divisions to form a **mature quadrinucleate cyst**. This 4-nucleated stage is the infective form for humans; it is resistant to gastric acid and environmental stressors. **Analysis of Incorrect Options:** * **Option A (1 nucleus):** This represents the early **uninucleate cyst**. While present in the life cycle, it is immature and not the diagnostic hallmark of a "mature" cyst. * **Option B (2 nuclei):** This represents the intermediate **binucleate cyst** stage. * **Option D (8 nuclei):** This is a classic "distractor" in NEET-PG. An 8-nucleated mature cyst is the characteristic feature of ***Entamoeba coli***, a non-pathogenic commensal. Differentiating between 4 nuclei (*E. histolytica*) and 8 nuclei (*E. coli*) is a frequent exam topic. **Clinical Pearls for NEET-PG:** * **Infective dose:** As few as 10–100 cysts can cause infection. * **Morphology:** Mature cysts also contain **chromidial bars** with rounded/blunt ends (cigar-shaped), composed of ribosomes. In contrast, *E. coli* chromidial bars have splintered/frayed ends. * **Excystation:** Occurs in the small intestine, where one quadrinucleate cyst gives rise to eight small metacystic trophozoites. * **Nuclear Morphology:** Look for a central **karyosome** and fine, uniform peripheral chromatin (the "bull's eye" appearance).

Question 657: Cysticercus cellulosae is a larval form seen in infection with which of the following parasites?

A. Taenia solium (Correct Answer)
B. Taenia saginata
C. Echinococcus granulosus
D. None of the above

Explanation: **Explanation:** The correct answer is **Taenia solium**. **Cysticercus cellulosae** is the larval stage of *Taenia solium* (Pork Tapeworm). In the normal life cycle, pigs ingest eggs and develop these larvae in their muscles. Humans typically become the definitive host by eating undercooked pork containing these larvae, leading to intestinal taeniasis. However, if a human accidentally ingests *T. solium* **eggs** (via contaminated food/water or autoinfection), they act as an accidental intermediate host. The eggs hatch, and the larvae (Cysticercus cellulosae) migrate to various tissues, most critically the brain, causing **Neurocysticercosis (NCC)**. **Analysis of Incorrect Options:** * **Taenia saginata (Beef Tapeworm):** Its larval form is called **Cysticercus bovis**. Unlike *T. solium*, humans are only definitive hosts for *T. saginata*; ingestion of eggs does not lead to cysticercosis in humans. * **Echinococcus granulosus (Dog Tapeworm):** The larval form of this parasite is the **Hydatid cyst**. It causes Hydatid disease, primarily affecting the liver and lungs. **NEET-PG High-Yield Pearls:** * **Definitive Host:** Human (for both *Taenia* species). * **Intermediate Host:** Pig (*T. solium*); Cattle (*T. saginata*). * **Infective Stage for Cysticercosis:** Eggs of *T. solium*. * **Infective Stage for Intestinal Taeniasis:** Cysticercus larvae in undercooked meat. * **Diagnostic Feature:** *T. solium* has a scolex with four suckers and a rostellum with hooks ("Armed Tapeworm"), whereas *T. saginata* lacks hooks ("Unarmed").

Question 658: 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?

A. Gastric biopsy
B. Muscle biopsy (Correct Answer)
C. Scotch tape test
D. Stool for ova and parasites

Explanation: ### 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.

Question 659: What is the infectious stage of Plasmodium?

A. Trophozoite
B. Cryptozoite
C. Sporozoite (Correct Answer)
D. Merozoite

Explanation: ### Explanation **Correct Answer: C. Sporozoite** The life cycle of *Plasmodium* involves two hosts: the female *Anopheles* mosquito (definitive host) and the human (intermediate host). The **sporozoite** is the infectious stage for humans. When an infected mosquito bites a human, it inoculates sporozoites from its salivary glands into the bloodstream. These sporozoites quickly migrate to the liver to initiate the **Pre-erythrocytic (Exo-erythrocytic) schizogony**. #### Analysis of Incorrect Options: * **A. Trophozoite:** This is the metabolically active, feeding stage found within the host's Red Blood Cells (RBCs). The "ring form" is the early trophozoite stage used for diagnosis on peripheral smears. * **B. Cryptozoite:** These are the progeny produced during the first generation of hepatic (liver) schizogony. They are not the stage that initiates infection upon entry. * **C. Merozoite:** These are released when a liver cell or an RBC ruptures. Merozoites are responsible for infecting new RBCs, leading to the clinical manifestations of malaria (fever paroxysms), but they are not the stage introduced by the mosquito. #### NEET-PG High-Yield Pearls: * **Infective stage for Mosquito:** Gametocytes (taken up during a blood meal). * **Site of Sporogony:** Occurs in the mosquito (extrinsic incubation period). * **Hypnozoites:** Dormant liver stages found in *P. vivax* and *P. ovale*, responsible for **relapse**. * **Recrudescence:** Seen in *P. falciparum* due to sub-therapeutic treatment or waning immunity (not from liver stages). * **Gold Standard Diagnosis:** Thick and thin peripheral blood smears (Giemsa stain).

Question 660: 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?

A. Naegleria fowleri (Correct Answer)
B. Entamoeba histolytica
C. Giardia lamblia
D. Trypanosoma species

Explanation: ### **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.

Practice by Chapter

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