Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 371: An AIDS patient presents with headaches and disorientation. A clinical diagnosis of Toxoplasma encephalitis is made, and Toxoplasma cysts are observed in a brain section. Which of the following antibody results would be most likely in this patient?

A. IgM nonreactive, IgG nonreactive
B. IgM nonreactive, IgG reactive (low titer) (Correct Answer)
C. IgM reactive (low titer), IgG reactive (high titer)
D. IgM reactive (high titer), IgG reactive (high titer)

Explanation: ### Explanation **1. Why Option B is Correct:** In patients with AIDS, Toxoplasma encephalitis is almost always a result of **reactivation of a latent infection** rather than a primary (new) infection. * **IgG:** Since the infection is a reactivation, the patient will have pre-existing IgG antibodies. However, because these patients are severely immunocompromised (typically CD4 <100 cells/mm³), they often fail to mount a robust anamnestic response, leading to **low or stable IgG titers**. * **IgM:** IgM is a marker of acute/primary infection. In reactivation cases, IgM is typically **nonreactive (negative)**. **2. Why Other Options are Incorrect:** * **Option A:** If both are nonreactive, it suggests the patient has never been exposed to *Toxoplasma gondii*. While rare cases of seronegative toxoplasmosis occur in profound immunosuppression, a reactive IgG is the standard diagnostic expectation for reactivation. * **Options C & D:** High titers of IgG and the presence of IgM are characteristic of **primary (acute) toxoplasmosis** in an immunocompetent host. In AIDS patients, the immune system is usually too suppressed to produce IgM or a high-titer IgG surge during reactivation. **3. Clinical Pearls for NEET-PG:** * **Most common cause** of CNS mass lesions in AIDS patients. * **Imaging:** Classic "Ring-enhancing lesions" on CT/MRI (often multiple and involving basal ganglia). * **Definitive Diagnosis:** Brain biopsy (showing tachyzoites or cysts), though usually diagnosed empirically. * **Prophylaxis:** Started when CD4 count <100 cells/mm³. Drug of choice: **Trimethoprim-Sulfamethoxazole (TMP-SMX)**. * **Treatment:** Pyrimethamine + Sulfadiazine + Folinic acid.

Question 372: Schistosomiasis is a disease characterized by granulomatous reactions to the ova or to products of the parasite at the place of oviposition. Clinical manifestations include which one of the following?

A. Bladder wall hyperplasia
B. Pulmonary embolism
C. Splenomegaly (Correct Answer)
D. Cardiac abnormalities

Explanation: **Explanation:** The clinical manifestations of Schistosomiasis (Bilharziasis) are primarily driven by the host’s **granulomatous immune response** to eggs trapped in tissues, rather than the adult worms themselves. **Why Splenomegaly is Correct:** In infections caused by *Schistosoma mansoni* and *S. japonicum*, adult worms reside in the mesenteric veins. Eggs are deposited and travel via the portal circulation to the liver, where they trigger periportal (Symmers' pipe-stem) fibrosis. This leads to **portal hypertension**, which subsequently causes congestive **splenomegaly** and esophageal varices. This "hepatosplenic schistosomiasis" is a classic presentation in chronic cases. **Analysis of Incorrect Options:** * **A. Bladder wall hyperplasia:** While *S. haematobium* affects the urinary tract, it typically causes bladder wall **calcification**, ulceration, and squamous cell carcinoma. "Hyperplasia" is not the characteristic pathological description used for these lesions. * **B. Pulmonary embolism:** While eggs can reach the lungs causing pulmonary hypertension (cor pulmonale), they do not typically cause classic thromboembolism. * **D. Cardiac abnormalities:** Heart involvement is rare and usually secondary to pulmonary hypertension (Right heart failure), not a primary manifestation of oviposition. **NEET-PG High-Yield Pearls:** * **Intermediate Host:** Freshwater snails (*Biomphalaria* for *S. mansoni*; *Bulinus* for *S. haematobium*). * **Infective Stage:** Cercaria (penetrates skin during swimming). * **Diagnostic Feature:** Eggs with spines (*S. haematobium*: Terminal spine; *S. mansoni*: Lateral spine). * **Drug of Choice:** Praziquantel. * **Katayama Fever:** An acute serum sickness-like reaction occurring weeks after infection.

Question 373: Dwarf tapeworm refers to which of the following?

A. Echinococcus
B. Loa Loa
C. Hymenolepsis nana (Correct Answer)
D. Schistosoma mansoni

Explanation: **Explanation:** **Hymenolepis nana (H. nana)** is known as the **Dwarf Tapeworm** because it is the smallest intestinal cestode infecting humans, typically measuring only 15–40 mm in length. **Why H. nana is the correct answer:** It is unique among tapeworms because it does not mandatory require an intermediate host; it can complete its entire life cycle in a single host (Man). It is the only cestode capable of **internal autoinfection**, where eggs hatch within the intestine and develop into larvae (cysticercoids) in the villi, leading to heavy parasite loads. **Analysis of Incorrect Options:** * **A. Echinococcus granulosus:** Known as the **Dog Tapeworm**. It causes Hydatid disease and is characterized by the formation of slow-growing cysts in the liver and lungs. * **B. Loa loa:** Known as the **African Eye Worm**. It is a nematode (roundworm) transmitted by the *Chrysops* fly, characterized by Calabar swellings and subconjunctival migration. * **C. Schistosoma mansoni:** Known as a **Blood Fluke**. It is a trematode that resides in the mesenteric veins and causes intestinal schistosomiasis and portal hypertension. **High-Yield Clinical Pearls for NEET-PG:** * **Smallest Cestode:** *H. nana* (Dwarf tapeworm). * **Largest Cestode:** *Diphyllobothrium latum* (Fish tapeworm). * **Infective Stage:** Embryonated eggs (most common) or cysticercoid larvae (via ingestion of infected insects). * **Diagnosis:** Stool microscopy showing characteristic eggs with **polar filaments** (distinguishes it from *H. diminuta*). * **Treatment of Choice:** Praziquantel.

Question 374: All the following diseases are spread by Hard Ticks except?

A. Relapsing fever (Correct Answer)
B. Kyasanur Forest Disease (KFD)
C. Tularemia
D. Tick paralysis

Explanation: **Explanation:** The correct answer is **Relapsing fever** because it is primarily transmitted by **Soft Ticks** (*Ornithodoros*) or **Lice**, rather than Hard Ticks. 1. **Why Relapsing Fever is the correct answer:** * **Endemic Relapsing Fever** is caused by *Borrelia duttoni* and is transmitted by the **Soft Tick** (*Ornithodoros moubata*). * **Epidemic Relapsing Fever** is caused by *Borrelia recurrentis* and is transmitted by the **Human Body Louse**. * Hard ticks (*Ixodidae*) do not serve as vectors for these specific pathogens. 2. **Analysis of Incorrect Options (Diseases spread by Hard Ticks):** * **Kyasanur Forest Disease (KFD):** A viral hemorrhagic fever transmitted by the hard tick *Haemaphysalis spinigera*. It is highly relevant in the Indian context (Karnataka). * **Tularemia:** Caused by *Francisella tularensis*, it can be transmitted by various hard ticks (e.g., *Dermacentor*, *Amblyomma*), as well as deer flies and direct animal contact. * **Tick Paralysis:** Caused by a neurotoxin in the saliva of certain female hard ticks (e.g., *Dermacentor andersoni*). It presents as an ascending flaccid paralysis. **High-Yield Clinical Pearls for NEET-PG:** * **Hard Ticks (Ixodidae):** Remember the mnemonic **"K-B-R-T"** (KFD, Babesiosis, Rocky Mountain Spotted Fever/Rickettsioses, Tularemia). They have a dorsal shield (scutum) and feed for long periods. * **Soft Ticks (Argasidae):** They lack a scutum and feed rapidly. The most important medical association is **Endemic Relapsing Fever**. * **Lyme Disease:** Also transmitted by a hard tick (*Ixodes ricinus/scapularis*).

Question 375: Strawberry appearance of the cervix is characteristically seen in which of the following conditions?

A. Candidiasis
B. Chlamydia infection
C. Genital herpes
D. Trichomoniasis (Correct Answer)

Explanation: **Explanation:** **Trichomoniasis** is caused by the flagellated protozoan *Trichomonas vaginalis*. The "Strawberry Cervix" (Colpitis macularis) is a pathognomonic clinical sign where the cervix appears erythematous with punctate hemorrhages. This occurs due to the inflammatory response and capillary dilation caused by the parasite. **Why the other options are incorrect:** * **Candidiasis:** Typically presents with a "cottage-cheese" like, thick white discharge and intense pruritus. The vaginal mucosa may be erythematous, but it does not show punctate hemorrhages. * **Chlamydia infection:** Often causes a mucopurulent cervicitis with an erythematous, friable cervix that bleeds easily on contact, but it lacks the specific "strawberry" appearance. * **Genital Herpes:** Characterized by painful, fluid-filled vesicles that rupture to form shallow, exquisitely tender ulcers. **High-Yield Clinical Pearls for NEET-PG:** * **Discharge:** Trichomoniasis features a **foul-smelling, frothy, greenish-yellow** discharge. * **Diagnosis:** The gold standard is **Culture (Diamond’s medium)**. However, the most common bedside test is **Wet Mount microscopy**, showing "jerky/twitchy motility." * **Vaginal pH:** In Trichomoniasis, the pH is typically **>4.5** (elevated). * **Treatment:** The drug of choice is **Metronidazole**. It is crucial to **treat the partner** simultaneously to prevent "ping-pong" reinfection. * **Whiff Test:** May be positive in Trichomoniasis, though more characteristic of Bacterial Vaginosis.

Question 376: Strawberry cervix is seen in which of the following conditions?

A. Gardenella vaginalis infection
B. Trichomonas vaginalis infection (Correct Answer)
C. Candida infection
D. Mycoplasma pneumoniae infection

Explanation: **Explanation:** **Trichomonas vaginalis infection** is the correct answer. The "Strawberry Cervix" (colpitis macularis) is a classic clinical sign characterized by punctate hemorrhages on the cervical epithelium. This occurs because the parasite causes intense local inflammation and capillary dilation, making the cervix appear red and speckled, resembling the surface of a strawberry. While highly specific for Trichomoniasis, it is only visible on physical examination in about 2-5% of cases (more frequently seen via colposcopy). **Analysis of Incorrect Options:** * **A. Gardnerella vaginalis:** This is the primary causative agent of Bacterial Vaginosis (BV). It is characterized by a "thin, homogenous, fishy-smelling discharge" and the presence of **Clue cells** on microscopy, but it does not cause a strawberry cervix. * **C. Candida infection:** Vulvovaginal Candidiasis typically presents with intense pruritus and a thick, white, **"curd-like" or "cottage cheese" discharge**. The vaginal mucosa may be erythematous, but it lacks the punctate hemorrhages of Trichomoniasis. * **D. Mycoplasma pneumoniae:** This is a respiratory pathogen responsible for atypical pneumonia and is not associated with vaginal or cervical infections. **NEET-PG High-Yield Pearls:** * **Trichomoniasis:** Caused by a flagellated protozoan. Look for **"frothy, yellowish-green, foul-smelling discharge"** and a vaginal pH > 4.5. * **Diagnosis:** The gold standard is **NAAT**, but the most common bedside test is **Wet Mount microscopy** showing "jerky/twitching motility." * **Treatment:** Drug of choice is **Metronidazole**. Crucially, the **partner must also be treated** to prevent reinfection (it is an STI). * **Whiff Test:** Positive (fishy odor with KOH) in both Bacterial Vaginosis and Trichomoniasis.

Question 377: What is the treatment of choice for Echinococcus granulosus?

A. Albendazole (Correct Answer)
B. Thio-bendazole
C. Mebendazole
D. Praziquantel

Explanation: **Explanation:** **Echinococcus granulosus**, the causative agent of Cystic Echinococcosis (Hydatid cyst), is primarily managed through a combination of surgery, aspiration (PAIR), and chemotherapy. **Why Albendazole is the Correct Choice:** **Albendazole** is the drug of choice because it is a broad-spectrum anthelmintic with superior pharmacokinetic properties compared to other benzimidazoles. It is a prodrug that is converted into **albendazole sulfoxide**, which achieves high concentrations in the hydatid cyst fluid and wall. It works by inhibiting microtubule synthesis, leading to glucose depletion and death of the scolex. In clinical practice, it is used as a primary treatment for small/multiple cysts or as an adjuvant before and after surgery/PAIR to reduce the risk of secondary seeding. **Analysis of Incorrect Options:** * **B. Thiabendazole:** While it is a benzimidazole, it is rarely used now due to significant systemic toxicity and lower efficacy compared to newer agents. * **C. Mebendazole:** It was previously used but is less effective than Albendazole because it is poorly absorbed from the gastrointestinal tract, leading to inconsistent therapeutic levels within the cyst. * **D. Praziquantel:** It is highly effective against adult tapeworms and is often used as an **adjunct** to Albendazole to kill protoscolices more rapidly, but it is not the primary "treatment of choice" for the cyst itself. **High-Yield Clinical Pearls for NEET-PG:** * **PAIR Technique:** Puncture, Aspiration, Injection (of scolicidal agents like hypertonic saline or 95% ethanol), and Re-aspiration. * **Diagnosis:** "Egg-shell calcification" on X-ray; "Water-lily sign" or "Camel-back sign" on USG/CT. * **Casoni’s Test:** An immediate hypersensitivity skin test (now largely replaced by ELISA). * **Surgical Precaution:** Extreme care must be taken to prevent cyst rupture, which can lead to life-threatening **anaphylaxis**.

Question 378: Which of the following is a flagellated amoeba?

A. Entamoeba histolytica
B. Naegleria fowleri (Correct Answer)
C. Acanthamoeba
D. Balamuthia

Explanation: **Explanation:** The correct answer is **Naegleria fowleri**. This organism is classified as a **Free-Living Amoeba (FLA)** and is unique because it is "amphizoic," meaning it can exist as both a free-living organism and a pathogen. **Why Naegleria fowleri is correct:** *Naegleria fowleri* is known as a **"transformer"** because it exists in three stages: the trophozoite, the cyst, and the **flagellated stage**. When environmental conditions change (such as a decrease in nutrient concentration or exposure to distilled water), the trophozoite develops two long flagella to move quickly to a more favorable environment. This transient flagellated form is a key diagnostic feature. **Why the other options are incorrect:** * **Entamoeba histolytica:** This is an obligate intestinal parasite. It exists only as a trophozoite (moving via pseudopodia) and a cyst. It never develops flagella. * **Acanthamoeba:** While it is a free-living amoeba, it only has two stages: trophozoite and cyst. It lacks a flagellated stage. It is characterized by "acanthopodia" (spine-like projections). * **Balamuthia:** Similar to *Acanthamoeba*, *Balamuthia mandrillaris* exists only in trophozoite and cyst forms and does not possess flagella. **High-Yield Clinical Pearls for NEET-PG:** * **Disease:** *Naegleria fowleri* causes **Primary Amoebic Meningoencephalitis (PAM)**, a rapidly fatal CNS infection typically seen in healthy children/young adults with a history of swimming in warm freshwater. * **Path of Entry:** Through the **cribriform plate** via the olfactory nerves. * **Diagnosis:** Wet mount of CSF shows **actively motile trophozoites**. Note: Only the trophozoite form is found in human tissue; cysts are not seen in brain sections (unlike *Acanthamoeba*). * **Drug of Choice:** Amphotericin B.

Question 379: The malaria card test for P. falciparum detects which antigen?

A. Lactate dehydrogenase (LDH)
B. Aldolase
C. Histidine-rich protein (Correct Answer)
D. None of the above

Explanation: **Explanation:** The Malaria Rapid Diagnostic Test (RDT), commonly known as the "Malaria Card Test," utilizes immunochromatographic techniques to detect specific parasite antigens in the blood. **Why Histidine-rich protein (HRP-2) is correct:** HRP-2 is a water-soluble protein produced specifically by **_Plasmodium falciparum_** during its growth and erythrocyte invasion. Because it is secreted into the bloodstream and remains stable, it serves as a highly sensitive biomarker. Most commercial "PF-only" or "Combo" cards use monoclonal antibodies against HRP-2 to identify _P. falciparum_ infections. **Analysis of Incorrect Options:** * **Lactate dehydrogenase (LDH):** While pLDH is used in RDTs, it is an enzyme produced by all four human malaria species. It is typically used as a marker for **pan-malarial** infection or to assess parasite viability (as LDH levels drop rapidly after successful treatment), rather than being the specific primary marker for _P. falciparum_ card tests. * **Aldolase:** Similar to LDH, aldolase is a glycolytic enzyme produced by all _Plasmodium_ species. It is used in "Pan-specific" RDTs to detect the presence of any malaria parasite (non-specific to _falciparum_). **NEET-PG High-Yield Pearls:** * **HRP-2 Persistence:** HRP-2 can persist in the blood for up to 2–4 weeks even after successful parasite clearance, leading to potential **false-positive** results in recently treated patients. * **Prozone Effect:** Very high parasitemia can sometimes cause a false-negative result in RDTs due to the prozone phenomenon. * **Species Specificity:** * **HRP-2:** Specific for _P. falciparum_. * **pLDH/Aldolase:** Common to all species (_P. vivax, P. falciparum, P. ovale, P. malariae_).

Question 380: In which type of malarial parasite is the exoerythrocytic stage absent?

A. P. ovale
B. P. vivax
C. P. falciparum (Correct Answer)
D. P. malariae

Explanation: ### Explanation The life cycle of *Plasmodium* in humans consists of two main stages: the **Exoerythrocytic (Hepatic) cycle** and the **Erythrocytic cycle**. The correct answer is **P. falciparum** (and also **P. malariae**). In these species, once the sporozoites enter the liver cells and mature into schizonts, they are released into the bloodstream to begin the erythrocytic phase. There is **no persistent liver stage** (hypnozoite). Once the liver is cleared, it remains clear unless a new mosquito bite occurs. **Analysis of Options:** * **P. vivax & P. ovale (Options A & B):** These species possess a "dormant" exoerythrocytic stage known as **hypnozoites**. These forms can remain latent in the liver for months or years, leading to **relapses** of malaria even after the blood stage has been treated. * **P. malariae (Option D):** Like *P. falciparum*, it lacks a true exoerythrocytic (hypnozoite) stage. However, it is known for **recrudescence** (survival of low-level parasites in the blood), not relapse from the liver. In many competitive exams, if both are options, *P. falciparum* is the classic textbook answer for the absence of a persistent liver phase. **High-Yield NEET-PG Pearls:** 1. **Relapse vs. Recrudescence:** Relapse is due to hypnozoites in the liver (*P. vivax/ovale*). Recrudescence is due to persistent sub-clinical parasites in the blood (*P. falciparum/malariae*). 2. **Drug of Choice for Hypnozoites:** **Primaquine** or **Tafenoquine** must be administered to achieve a "radical cure" in *P. vivax* and *P. ovale* infections. 3. **Primaquine Caution:** Always screen for **G6PD deficiency** before administration to prevent acute hemolysis. 4. **P. falciparum** is the most common cause of cerebral malaria and lacks the Schuffner’s dots seen in *P. vivax*.

Practice by Chapter

Classification of Parasites

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Intestinal Protozoa

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Blood and Tissue Protozoa

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Malaria Parasites

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Leishmaniasis

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Intestinal Helminths: Nematodes

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Tissue Nematodes

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Trematodes

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Cestodes

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Ectoparasites

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Antiparasitic Drugs

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Laboratory Diagnosis of Parasitic Infections

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