Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 181: Terminal spined eggs are seen in which parasite?

A. Schistosoma haematobium (Correct Answer)
B. Schistosoma mansoni
C. Schistosoma Japonicum
D. Chlonorchis sinensis

Explanation: The identification of *Schistosoma* species is a high-yield topic in NEET-PG, primarily based on the morphology of their eggs. **Correct Answer: A. Schistosoma haematobium** *Schistosoma haematobium* is uniquely characterized by eggs that possess a distinct **terminal spine** at one end. These eggs are typically excreted in the **urine** (and occasionally feces). Clinically, this parasite inhabits the vesical venous plexuses, leading to hematuria and an increased risk of squamous cell carcinoma of the urinary bladder. **Explanation of Incorrect Options:** * **B. Schistosoma mansoni:** These eggs are characterized by a prominent **lateral spine**. They are found in the feces and are associated with intestinal schistosomiasis and portal hypertension. * **C. Schistosoma japonicum:** These eggs are more rounded/oval and possess a very small, inconspicuous **lateral knob** (rudimentary spine) rather than a prominent spine. * **D. Clonorchis sinensis:** Also known as the Chinese Liver Fluke, its eggs are much smaller, flask-shaped, and possess an **operculum** (lid) at one pole and a small knob at the other, but they do not have spines. **High-Yield Clinical Pearls for NEET-PG:** * **Intermediate Host:** All Schistosomes require **snails** as intermediate hosts (e.g., *Bulinus* for *S. haematobium*). * **Infective Stage:** **Cercaria** (penetrates unbroken skin during swimming). * **Diagnostic Test:** Urine microscopy (10 AM to 2 PM sample) for *S. haematobium*; Kat-Katz technique for stool samples. * **Drug of Choice:** **Praziquantel** is the gold standard for all Schistosoma species.

Question 182: Casoni's test is used in the diagnosis of:

A. Sarcoidosis
B. Hydatid disease (Correct Answer)
C. Kala-azar
D. Cutaneous microfilaria

Explanation: **Explanation:** **Casoni’s test** is an immediate hypersensitivity skin test (Type I Hypersensitivity) used for the diagnosis of **Hydatid disease**, caused by the larval stage of the tapeworm *Echinococcus granulosus*. 1. **Why Hydatid Disease is correct:** The test involves the intradermal injection of 0.2 ml of sterile "hydatid fluid" (derived from human or sheep cysts). A positive result is indicated by the formation of a large wheal (>1.5 cm) with pseudopodia within 20 minutes. While historically significant, it has largely been replaced by more specific serological tests (ELISA) and imaging (USG/CT) due to its low specificity and risk of anaphylaxis. 2. **Why other options are incorrect:** * **Sarcoidosis:** The diagnostic skin test for Sarcoidosis is the **Kveim-Siltzbach test**, which uses an injection of spleen/lymph node extract from a known sarcoid patient. * **Kala-azar (Visceral Leishmaniasis):** The **Montenegro (Leishmanin) skin test** is used here. It is a delayed-type hypersensitivity (Type IV) test, which is typically negative in active Kala-azar but positive in recovered patients or those with Post-Kala-azar Dermal Leishmaniasis (PKDL). * **Cutaneous Microfilaria:** Diagnosis is primarily made via skin snip biopsy or peripheral blood smears. There is no specific "Casoni-like" skin test routinely used for microfilaria. **High-Yield Facts for NEET-PG:** * **Gold Standard Diagnosis:** Ultrasonography (WHO classification: CL to CE5) is the primary tool for Hydatid disease. * **Serology:** ELISA for IgG antibodies is the preferred screening method. * **Treatment Pearl:** The **PAIR** technique (Puncture, Aspiration, Injection, Re-aspiration) is used for certain cyst stages, always under the cover of **Albendazole** to prevent secondary hydatidosis from spillage.

Question 183: Which is not a feature of tropical eosinophilia?

A. Eosinophilia greater than 3000/mm3
B. Microfilaria in tissue
C. Microfilaria in blood (Correct Answer)
D. Lymphadenopathy

Explanation: **Explanation:** Tropical Pulmonary Eosinophilia (TPE) is a distinct clinical manifestation of lymphatic filariasis (caused by *Wuchereria bancrofti* or *Brugia malayi*). It represents a **hypersensitivity reaction** (Type I and Type IV) to the microfilarial antigens rather than a typical infection. **Why "Microfilaria in blood" is the correct answer:** In TPE, the immune system becomes hyper-responsive and rapidly clears microfilariae from the peripheral circulation. The microfilariae are trapped and destroyed in the pulmonary capillaries and reticuloendothelial tissues. Consequently, **microfilariae are characteristically absent from the peripheral blood**, making this a "cryptic" form of filariasis. **Analysis of other options:** * **A. Eosinophilia >3000/mm³:** This is a hallmark feature. Patients typically present with massive absolute eosinophil counts, often exceeding 3,000/mm³ (frequently >10,000/mm³). * **B. Microfilaria in tissue:** While absent in blood, degenerating microfilariae can be found in lung biopsies, liver, or lymph nodes, often surrounded by eosinophilic aggregates (Meyers-Kouwenaar bodies). * **D. Lymphadenopathy:** Along with hepatosplenomegaly, lymphadenopathy is a common systemic finding in TPE due to the generalized immune activation. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Triad:** Paroxysmal nocturnal cough/wheezing, massive eosinophilia, and high serum IgE levels (>1000 units/ml). * **Chest X-ray:** Shows bilateral diffuse miliary mottling or increased bronchovascular markings (predominantly in lower zones). * **Drug of Choice:** **Diethylcarbamazine (DEC)** for 21 days. A rapid clinical response to DEC is often used as a diagnostic criterion. * **Key Difference:** Unlike classical filariasis, TPE does not typically present with lymphedema or elephantiasis.

Question 184: Which of the following organisms uses man as an intermediate host?

A. Brugia malayi
B. Wuchereria bancrofti
C. Plasmodium (Correct Answer)
D. Taenia saginata

Explanation: ### Explanation In parasitology, the classification of hosts is determined by the stage of the parasite's life cycle: * **Definitive Host:** Where the **sexual cycle** occurs or the adult parasite resides. * **Intermediate Host:** Where the **asexual cycle** occurs or the larval stages develop. **Why Plasmodium is Correct:** In the life cycle of *Plasmodium* (Malaria), the **sexual cycle (sporogony)** occurs within the female *Anopheles* mosquito, making it the definitive host. The **asexual cycle (schizogony)** occurs in humans (hepatic and erythrocytic stages), thus making **man the intermediate host**. **Analysis of Incorrect Options:** * **Brugia malayi & Wuchereria bancrofti:** For these filarial nematodes, **man is the definitive host** because the adult worms reside in the human lymphatic system. The mosquito acts as the intermediate host where larval development (L1 to L3) occurs. * **Taenia saginata (Beef Tapeworm):** **Man is the definitive host** (harbors the adult worm in the intestine). Cattle serve as the intermediate host. *Note: In Taenia solium, man can be both the definitive host (taeniasis) and the accidental intermediate host (cysticercosis).* **NEET-PG High-Yield Pearls:** * **Man as Intermediate Host:** Remember the mnemonic **"MPT"** — **M**alaria (*Plasmodium*), **P**neumocystis (rarely asked this way), and **T**oxoplasma. Also includes *Echinococcus granulosus* (Hydatid disease). * **Exception:** In *Hymenolepis nana*, man serves as both definitive and intermediate host in the same individual. * **Accidental Host:** Man is the "dead-end" intermediate host for *Echinococcus granulosus* and *Toxocara canis*.

Question 185: A man presented with diarrhea and lower abdominal pain. The stool is heme-positive. What is the investigation of choice for amoebiasis?

A. ELISA
B. Colonoscopy
C. Microscopy
D. Microscopy and ELISA (Correct Answer)

Explanation: **Explanation:** The diagnosis of intestinal amoebiasis (caused by *Entamoeba histolytica*) relies on distinguishing the pathogen from non-pathogenic commensals like *E. dispar*. 1. **Why "Microscopy and ELISA" is correct:** While **microscopy** is the traditional first-line test to visualize trophozoites (containing ingested RBCs) or quadrinucleate cysts, it has low sensitivity (approx. 60%) and cannot morphologically distinguish *E. histolytica* from *E. dispar*. **ELISA** for fecal antigen detection (specifically targeting the Gal/GalNAc lectin) provides high specificity and sensitivity, allowing for definitive identification of the pathogen. Combining both methods maximizes diagnostic yield and accuracy. 2. **Why other options are incorrect:** * **ELISA (Option A):** While highly specific, relying solely on ELISA may miss cases if the antigen load is low; microscopy remains a necessary screening tool. * **Colonoscopy (Option B):** This is an invasive procedure. While it may show characteristic "flask-shaped ulcers," it is reserved for cases where stool studies are negative but clinical suspicion remains high. * **Microscopy (Option C):** Insufficient as a standalone test due to its inability to differentiate species and its dependence on the skill of the microscopist. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic finding:** Trophozoites with **ingested RBCs** (Erythrophagocytosis) in stool microscopy. * **Stain of choice:** Iron-hematoxylin or Trichrome stain. * **Serology:** Serum antibody ELISA is more useful for **Extra-intestinal amoebiasis** (e.g., Amoebic Liver Abscess) than for intestinal disease. * **Treatment:** Luminal agents (Diloxanide furoate/Paromomycin) are needed even in asymptomatic cyst passers to prevent transmission.

Question 186: In vivax and ovale malaria, relapses are due to which of the following?

A. Bradyzoites
B. Merozoites
C. Hypnozoites (Correct Answer)
D. Sporozoites

Explanation: **Explanation:** The correct answer is **Hypnozoites**. In the life cycle of *Plasmodium vivax* and *Plasmodium ovale*, some sporozoites do not immediately undergo exo-erythrocytic schizogony upon entering the liver. Instead, they enter a dormant phase known as **hypnozoites** (derived from "hypnos," meaning sleep). These dormant forms can remain in the liver for weeks, months, or even years. When they eventually reactivate, they initiate a new cycle of erythrocytic infection, leading to a clinical **relapse**. **Analysis of Incorrect Options:** * **Bradyzoites (A):** These are the slow-growing, dormant stages of *Toxoplasma gondii* found within tissue cysts. They are not associated with the Malaria parasite. * **Merozoites (B):** These are the stages released from liver schizonts (exo-erythrocytic) or red blood cells (erythrocytic). They are responsible for the clinical symptoms of malaria but do not cause relapses through dormancy. * **Sporozoites (D):** This is the infectious stage injected by the female Anopheles mosquito. While they initiate the primary infection, they do not persist in a dormant state themselves; they either transform into schizonts or hypnozoites. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** **Primaquine** (or Tafenoquine) is the only drug effective against hypnozoites (radical cure). It must be avoided in patients with **G6PD deficiency** due to the risk of acute hemolysis. * **Recrudescence vs. Relapse:** *P. falciparum* and *P. malariae* do **not** have hypnozoites; they cause "recrudescence" due to the persistence of sub-clinical parasites in the blood, not "relapse" from the liver. * **Schüffner’s dots:** Characteristically seen in RBCs infected with *P. vivax* and *P. ovale*.

Question 187: Which of the following is true about amoebic colitis?

A. Caused by Entamoeba histolytica (Correct Answer)
B. The cyst contains eight nuclei
C. Flask-shaped ulcers are present
D. The cecum is most commonly affected

Explanation: **Explanation:** Amoebic colitis is an intestinal infection caused by the protozoan parasite **Entamoeba histolytica**. It is a significant cause of diarrheal disease worldwide, particularly in areas with poor sanitation. **1. Why Option A is correct:** *Entamoeba histolytica* is the definitive causative agent of amoebiasis. It exists in two stages: the infective **quadrinucleate cyst** and the invasive **trophozoite**. The trophozoites invade the intestinal mucosa by secreting proteolytic enzymes (histolysins), leading to tissue destruction and colitis. **2. Analysis of Incorrect Options:** * **Option B:** The mature infective cyst of *E. histolytica* contains **four nuclei** (quadrinucleate). A cyst with eight nuclei is characteristic of *Entamoeba coli*, which is a non-pathogenic commensal. * **Option C:** While **flask-shaped ulcers** are indeed a classic pathological hallmark of amoebic colitis, the question asks for the most fundamental truth. (Note: In many competitive exams, if multiple statements are technically true, the primary definition or the most specific causative agent is prioritized. However, in standard pathology, C is also a "true" feature. In the context of this specific MCQ structure, A is the primary identification). * **Option D:** The **cecum and ascending colon** are the most common sites for amoebic lesions due to stasis of contents, followed by the sigmoid colon and rectum. **High-Yield Clinical Pearls for NEET-PG:** * **Pathology:** The "flask-shaped" ulcer has a narrow neck and a broad base. * **Microscopy:** Look for trophozoites containing **ingested RBCs** (erythrophagocytosis)—this is pathognomonic for *E. histolytica* and distinguishes it from the morphologically identical *E. dispar*. * **Complications:** The most common extra-intestinal site is the liver (**Amoebic Liver Abscess**), typically presenting with "anchovy sauce" pus. * **Treatment:** Drug of choice for symptomatic colitis is **Metronidazole** or Tinidazole, followed by a luminal amebicide (e.g., Paromomycin or Diloxanide furoate) to eradicate cysts.

Question 188: Which of the following statements is TRUE regarding visceral leishmaniasis?

A. It is caused by L. tropica.
B. Post-leishmaniasis dermatitis is common.
C. Antimonials are useful drugs for its treatment. (Correct Answer)
D. It is diagnosed by blood smear.

Explanation: **Explanation:** **Visceral Leishmaniasis (Kala-azar)** is a systemic protozoal infection caused by the *Leishmania donovani* complex, transmitted by the bite of the female sandfly (*Phlebotomus argentipes*). 1. **Why Option C is Correct:** **Pentavalent Antimonials** (e.g., Sodium Stibogluconate and Meglumine Antimoniate) have historically been the mainstay of treatment. While resistance is increasing (especially in Bihar, India), they remain a classic pharmacological association for the disease. Currently, **Liposomal Amphotericin B** is the drug of choice due to higher efficacy and lower toxicity. 2. **Why Other Options are Incorrect:** * **Option A:** *L. tropica* and *L. major* cause **Cutaneous Leishmaniasis** (Oriental Sore). Visceral Leishmaniasis is caused by *L. donovani* and *L. infantum*. * **Option B:** The correct term is **Post-Kala-azar Dermal Leishmaniasis (PKDL)**, not "dermatitis." PKDL is a non-ulcerative skin condition that develops months to years after the apparent cure of visceral leishmaniasis, acting as a reservoir for the parasite. * **Option D:** Diagnosis is primarily through **bone marrow or splenic aspiration** (demonstrating Amastigote/LD bodies). Blood smears are rarely sensitive enough; however, the rK39 immunochromatographic test is the preferred rapid diagnostic tool. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad:** Fever, massive splenomegaly, and significant weight loss (cachexia). * **Hematology:** Characterized by **Pancytopenia** and **Hypergammaglobulinemia** (reversed Albumin:Globulin ratio). * **Napier’s Aldehyde Test:** A non-specific screening test based on elevated serum globulins. * **Culture:** NNN (Novy-MacNeal-Nicolle) medium is used to grow the Promastigote stage.

Question 189: Acute toxoplasmosis is commonly associated with all of the following except?

A. Cervical lymphadenopathy
B. Axillary lymphadenopathy
C. Muscle pain
D. Myocarditis (Correct Answer)

Explanation: **Explanation:** **Toxoplasmosis**, caused by the protozoan *Toxoplasma gondii*, presents differently depending on the host's immune status. In **immunocompetent individuals**, acute infection is asymptomatic in 80–90% of cases. When symptoms do occur, the most common clinical manifestation is **painless lymphadenopathy**. 1. **Why Myocarditis is the Correct Answer:** While *Toxoplasma* can theoretically affect any organ, **myocarditis** is an extremely rare complication in acute, immunocompetent cases. It is typically seen only in **severely immunocompromised patients** (e.g., advanced HIV/AIDS) or as part of a disseminated infection in neonates. Therefore, it is not "commonly associated" with standard acute toxoplasmosis. 2. **Analysis of Incorrect Options:** * **Cervical and Axillary Lymphadenopathy (Options A & B):** These are the hallmark signs of acute toxoplasmosis. The cervical nodes are most frequently involved, followed by axillary and inguinal nodes. The nodes are usually discrete and non-suppurative. * **Muscle Pain (Option C):** A "mononucleosis-like syndrome" is common in acute toxoplasmosis, characterized by fever, headache, fatigue, and **myalgia** (muscle pain) due to the systemic spread of tachyzoites. **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Cat (sexual cycle occurs in the intestinal epithelium). * **Intermediate Host:** Humans and other mammals (asexual cycle). * **Infective Forms:** Oocysts (from cat feces), Tissue cysts (undercooked meat), and Tachyzoites (transplacental). * **Diagnosis:** Serology (Sabin-Feldman Dye Test is the gold standard; IgM indicates acute infection). * **Congenital Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Treatment of Choice:** Pyrimethamine + Sulfadiazine (with Folinic acid).

Question 190: Which of the following is characteristic of a hemoflagellate?

A. Requires an intermediate host (Correct Answer)
B. Grows in living tissue
C. Does not grow in culture media
D. Has an undulating membrane

Explanation: **Explanation:** Hemoflagellates (Genera: *Leishmania* and *Trypanosoma*) are obligate heteroxenous parasites, meaning they **require an intermediate host** (an insect vector) to complete their life cycle. They alternate between a vertebrate host (man) and an invertebrate host (sandfly or tsetse/triatomine bug). This complex life cycle involves distinct morphological stages like amastigotes, promastigotes, epimastigotes, and trypomastigotes. **Analysis of Options:** * **Option A (Correct):** All medically important hemoflagellates are transmitted by insect vectors (e.g., *Leishmania* by Sandfly, *T. brucei* by Tsetse fly). * **Option B (Incorrect):** While they inhabit living tissue, this is not a defining characteristic unique to hemoflagellates; many other parasites (like *Toxoplasma*) also grow in living tissue. * **Option C (Incorrect):** Hemoflagellates **can** be grown in specialized artificial culture media. The most common is **NNN (Novy-MacNeal-Nicolle) medium**, where they typically grow in the promastigote or epimastigote stage. * **Option D (Incorrect):** While *Trypanosoma* species possess an undulating membrane, *Leishmania* species (specifically the amastigote form found in humans) do not. Therefore, it is not a characteristic shared by all hemoflagellates. **NEET-PG High-Yield Pearls:** * **Kinetoplast:** A specialized mitochondrial DNA structure found in all hemoflagellates, located near the base of the flagellum. * **Culture:** NNN medium is the gold standard; look for "water of condensation" where the parasites multiply. * **Vector Summary:** * *Leishmania donovani*: Female Sandfly (*Phlebotomus*). * *Trypanosoma cruzi*: Triatomine (Reduviid) bug. * *Trypanosoma brucei*: Tsetse fly (*Glossina*).

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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