Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 121: Which of the following is NOT true about toxoplasmosis?

A. In adults, toxoplasmosis is usually asymptomatic.
B. IgG antibodies are diagnostic in congenital toxoplasmosis. (Correct Answer)
C. It is an antroponotic disease.
D. Encephalitis is uncommon (rare) in immunocompetent individuals.

Explanation: ### Explanation **Why Option B is the correct answer (False statement):** In congenital toxoplasmosis, **IgG antibodies are NOT diagnostic**. Maternal IgG antibodies (specifically IgG) can cross the placenta and persist in the infant’s circulation for up to 6–12 months. Therefore, a positive IgG test in a neonate may simply reflect maternal infection rather than active fetal infection. To diagnose congenital toxoplasmosis, the detection of **IgM or IgA antibodies** in the neonate is required, as these large molecules do not cross the placenta and their presence indicates a fetal immune response. **Analysis of other options:** * **Option A:** In immunocompetent adults, *Toxoplasma gondii* infection is **asymptomatic in approximately 80–90%** of cases. When symptoms occur, they are usually mild and self-limiting (e.g., lymphadenopathy). * **Option C:** Toxoplasmosis is **NOT an anthroponotic disease** (human-to-human). It is a **zoonotic** disease. While the question asks for the "NOT true" statement, Option B is the primary clinical "falsehood" tested in exams. However, technically, Toxoplasma is a classic zoonosis with felids (cats) as definitive hosts. * **Option D:** Toxoplasmic encephalitis is a reactivation disease seen almost exclusively in **immunocompromised** patients (especially those with HIV/AIDS and CD4 counts <100 cells/μL). It is extremely rare in immunocompetent individuals. **High-Yield Clinical Pearls for NEET-PG:** * **Definitive Host:** Domestic cat (sexual cycle occurs in the intestinal epithelium). * **Infective Forms:** Oocysts (from cat feces), Tissue cysts (undercooked meat), and Tachyzoites (transplacental). * **Sabin-Feldman Dye Test:** The gold standard serological test (detects IgG). * **Congenital Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Imaging:** "Ring-enhancing lesions" on Brain MRI/CT in AIDS patients. * **Treatment:** Pyrimethamine + Sulfadiazine (plus Folinic acid to prevent bone marrow suppression).

Question 122: Which statement is true regarding malaria?

A. Rods forms are seen in Plasmodium malariae
B. Red blood cell size is increased in Plasmodium vivax infections (Correct Answer)
C. Relapse is seen in Plasmodium falciparum infections
D. Both male and female Anopheles mosquitoes transmit the disease

Explanation: **Explanation:** **1. Why Option B is Correct:** *Plasmodium vivax* and *Plasmodium ovale* have a specific predilection for infecting **young red blood cells (reticulocytes)**. These immature cells are naturally larger and more flexible than mature erythrocytes. As the parasite grows into the trophozoite stage (the "amoeboid" form), it further distends the host cell, making the infected RBC appear significantly enlarged and pale compared to neighboring uninfected cells. **2. Why the Other Options are Incorrect:** * **Option A:** **Ziemann’s dots** (not rods) are seen in *P. malariae*. "Rod" or "Cigar" shaped gametocytes are characteristic of *P. falciparum*. *P. malariae* is typically associated with "Band forms." * **Option C:** Relapse occurs due to **hypnozoites** (dormant liver stages), which are only found in *P. vivax* and *P. ovale*. *P. falciparum* does not have a hypnozoite stage; instead, it may show **recrudescence** due to the survival of erythrocytic forms in the blood. * **Option D:** Only **female** *Anopheles* mosquitoes transmit malaria. They require a blood meal for egg production, whereas males feed on plant nectar. **3. High-Yield NEET-PG Pearls:** * **Schüffner’s dots:** Seen in *P. vivax* and *P. ovale*. * **Maurer’s clefts:** Seen in *P. falciparum*. * **Multiple rings/Accole forms:** Highly suggestive of *P. falciparum*. * **Drug of Choice for Relapse:** Primaquine (contraindicated in G6PD deficiency). * **RBC Age Preference:** *P. vivax* (Young RBCs), *P. malariae* (Old RBCs), *P. falciparum* (All ages—hence high parasitemia).

Question 123: K 39 antigen is used in the diagnosis of which disease?

A. Malaria
B. Typhus fever
C. Kala azar (Correct Answer)
D. Enteric fever

Explanation: **Explanation:** **K39 (rK39)** is a recombinant protein derived from a 39-amino acid repeat unit found in a kinesin-like gene of ***Leishmania donovani***. It is the gold standard for the serological diagnosis of **Kala-azar (Visceral Leishmaniasis)** in field settings. 1. **Why Kala-azar is correct:** The rK39 antigen is highly sensitive (up to 98%) and specific for detecting antibodies against *L. donovani*. It is typically used in an **Immunochromatographic Test (ICT)** format (rapid dipstick test). A positive result indicates a current or past infection, as antibodies can persist for months after clinical cure. 2. **Why other options are incorrect:** * **Malaria:** Diagnosis primarily relies on peripheral blood smears (Gold standard) or **Rapid Diagnostic Tests (RDTs)** targeting antigens like **HRP-2** (*P. falciparum*) or **Parasite Lactate Dehydrogenase (pLDH)**. * **Typhus Fever:** Caused by *Rickettsia* species. Diagnosis is traditionally via the **Weil-Felix reaction** (heterophile agglutination) or specific immunofluorescence assays (IFA). * **Enteric Fever:** Caused by *Salmonella Typhi/Paratyphi*. Diagnosis involves **Blood culture** (1st week), **Widal test** (2nd week), or stool/urine cultures in later stages. **High-Yield Clinical Pearls for NEET-PG:** * **RK39 Limitations:** It cannot distinguish between active infection and past relapse/recovery. It may also be negative in HIV-coinfected patients due to poor antibody response. * **Montenegro Skin Test:** This is **negative** in active Kala-azar but becomes positive after recovery (delayed hypersensitivity). * **Definitive Diagnosis:** Demonstration of **LD bodies** (Amastigotes) in bone marrow or splenic aspirates. Splenic aspirate is more sensitive but carries a risk of hemorrhage.

Question 124: Iron deficiency anemia is associated with which type of helminth?

A. Ascaris lumbricoides
B. Ancylostoma duodenale/Necator americanus (Correct Answer)
C. Taenia species
D. Dipylidium caninum

Explanation: **Explanation:** **Ancylostoma duodenale** and **Necator americanus**, commonly known as hookworms, are the primary helminths associated with **Iron Deficiency Anemia (IDA)**. The underlying mechanism is chronic intestinal blood loss. These parasites attach to the small intestinal mucosa using buccal capsules (teeth in *A. duodenale* or cutting plates in *N. americanus*). They secrete anticoagulants (e.g., factor Xa inhibitors) and actively suck blood from the host capillaries. A single *A. duodenale* can cause up to 0.2 ml of blood loss per day, leading to microcytic hypochromic anemia when the host's iron stores are depleted. **Analysis of Incorrect Options:** * **Ascaris lumbricoides:** Primarily causes malnutrition, Vitamin A deficiency, and intestinal obstruction. While it competes for nutrients, it does not suck blood or cause significant IDA. * **Taenia species:** *T. saginata* and *T. solium* usually cause vague abdominal symptoms or cysticercosis. They do not cause significant blood loss. * **Dipylidium caninum:** A common tapeworm of dogs/cats that occasionally infects children; it is generally asymptomatic and not linked to anemia. **High-Yield Clinical Pearls for NEET-PG:** * **Ground Itch:** The pruritic dermatitis at the site of larval entry (skin penetration). * **Loeffler’s Syndrome:** Transient eosinophilic pneumonia occurring during the pulmonary migration phase of hookworms and *Ascaris*. * **Diagnosis:** Presence of non-bile stained, oval, segmented eggs with a clear space between the shell and embryo on stool microscopy. * **Treatment:** Albendazole (400mg single dose) is the drug of choice.

Question 125: Which of the following infections is not transmitted by the ingestion of contaminated food or water?

A. Leishmaniasis (Correct Answer)
B. Taenia solium
C. Guinea worm
D. Toxoplasmosis

Explanation: ### Explanation The correct answer is **Leishmaniasis**. This question tests your knowledge of the modes of transmission of common parasites. **1. Why Leishmaniasis is the correct answer:** Leishmaniasis (caused by *Leishmania donovani*) is a **vector-borne disease**. It is transmitted to humans through the bite of an infected female **Phlebotomine sandfly**. It is not transmitted via the fecal-oral route or ingestion of contaminated food/water. **2. Analysis of incorrect options:** * **Taenia solium (Pork Tapeworm):** Transmitted by the ingestion of undercooked pork containing cysticerci (Taeniasis) or by the ingestion of food/water contaminated with eggs (Cysticercosis). * **Guinea worm (*Dracunculus medinensis*):** Transmitted by drinking water containing **Cyclops** (water fleas) infected with L3 larvae. * **Toxoplasmosis (*Toxoplasma gondii*):** Primarily transmitted by the ingestion of oocysts from soil/water contaminated by cat feces or by eating undercooked meat containing tissue cysts. **Clinical Pearls for NEET-PG:** * **Sandfly Facts:** The sandfly is also the vector for *Bartonella bacilliformis* (Carrion's disease) and Sandfly fever (Pappataci fever). * **Leishmaniasis Diagnosis:** The gold standard is the demonstration of **Amastigotes (LD bodies)** in bone marrow or splenic aspirates. * **Guinea Worm:** India was declared Guinea worm-free in 2000. It is the only parasitic disease currently targeted for global eradication without a vaccine or medicine, solely through water filtration. * **Toxoplasmosis:** It is a classic "TORCH" infection; look for the triad of chorioretinitis, hydrocephalus, and intracranial calcifications in congenital cases.

Question 126: What is the method for diagnosing Hydatid disease?

A. Biopsy
B. X-ray
C. Casoni test
D. Serum examination (Correct Answer)

Explanation: **Explanation:** Hydatid disease, caused by the larval stage of *Echinococcus granulosus*, is primarily diagnosed through a combination of imaging and serology. **1. Why Serum Examination is the Correct Answer:** Serology (Serum examination) is the mainstay of diagnosis. It detects specific antibodies (IgG) against hydatid antigens. The most commonly used tests include **ELISA** and **Indirect Hemagglutination (IHA)**. For confirmation, the **Immunoblot (Western Blot)** for the 'Arc 5' antigen is highly specific. Serology is preferred because it is non-invasive and carries no risk of anaphylaxis. **2. Why Other Options are Incorrect:** * **Biopsy (A):** This is strictly **contraindicated**. Aspiration or biopsy of a hydatid cyst can lead to the leakage of hydatid fluid, which contains highly antigenic protoscolices. This can trigger life-threatening **anaphylactic shock** or lead to secondary peritoneal hydatidosis (seeding). * **X-ray (B):** While X-rays may show a "water lily sign" or calcification of the cyst wall, they are non-specific and less sensitive than Ultrasound or CT scans. * **Casoni Test (C):** This is an immediate hypersensitivity skin test. While historically important, it is now **obsolete** due to low sensitivity, low specificity, and the risk of inducing sensitivity in the patient. **Clinical Pearls for NEET-PG:** * **Gold Standard Imaging:** Ultrasound is the first-line investigation (look for "Gharbi classification"). * **Treatment of Choice:** Surgical excision (PAIR technique: Puncture, Aspiration, Injection, Re-aspiration) combined with **Albendazole**. * **Microscopy:** Look for "Hydatid sand" (protoscolices, hooklets, and calcareous corpuscles) in the fluid. * **Eosinophilia:** Present in only about 20-25% of cases; its absence does not rule out the disease.

Question 127: Espundia is a condition seen in which of the following?

A. Endemic syphilis
B. Malaria
C. Lymphogranuloma venereum
D. Mucocutaneous leishmaniasis (Correct Answer)

Explanation: **Explanation:** **Espundia** is the clinical term for **Mucocutaneous Leishmaniasis**, a chronic granulomatous disease caused primarily by the *Leishmania braziliensis* complex. It occurs when the parasite spreads from an initial skin lesion via the lymphatic or hematogenous route to the mucous membranes of the nose, mouth, and pharynx. This leads to progressive, disfiguring destruction of the nasal septum and soft tissues (often referred to as "Tapir nose"). **Analysis of Options:** * **Option D (Correct):** Espundia is specifically associated with New World Leishmaniasis. It is transmitted by the bite of the **Sandfly** (*Lutzomyia*). * **Option A (Incorrect):** Endemic syphilis (Bejel) is caused by *Treponema pallidum endemicum* and presents with oral papules and gummas, but is not termed Espundia. * **Option B (Incorrect):** Malaria is caused by *Plasmodium* species and presents with paroxysmal fever and splenomegaly, involving the RBCs rather than mucosal destruction. * **Option C (Incorrect):** Lymphogranuloma venereum (LGV) is caused by *Chlamydia trachomatis* (L1-L3) and primarily affects the inguinal lymph nodes (Groove sign). **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** Sandfly (*Phlebotomus* in Old World; *Lutzomyia* in New World). * **Diagnostic Gold Standard:** Demonstration of **LD bodies** (Amastigotes) in macrophages on Giemsa stain. * **Culture:** NNN (Novy-MacNeal-Nicolle) medium shows Promastigotes. * **Montenegro Skin Test:** Positive in Mucocutaneous and Cutaneous forms, but **negative** in active Visceral Leishmaniasis (Kala-azar). * **Drug of Choice:** Liposomal Amphotericin B or Sodium Stibogluconate.

Question 128: Transmission of all of the following intestinal parasites takes place by the feco-oral route except?

A. Giardia lambia
B. Ascaris lumbricoides
C. Strongyloides (Correct Answer)
D. Entamoeba histolytica

Explanation: **Explanation:** The core concept tested here is the **mode of transmission** of common intestinal parasites. While many intestinal parasites follow the feco-oral route (ingestion of eggs or cysts), others utilize **skin penetration** by larval forms. **Why Strongyloides is the correct answer:** *Strongyloides stercoralis* (Threadworm) is primarily transmitted via **larval skin penetration**. The filariform larvae present in contaminated soil penetrate the intact skin of a human host (usually through bare feet), enter the venous circulation, and migrate to the lungs before reaching the small intestine. It does not require ingestion for infection. **Analysis of Incorrect Options:** * **Giardia lamblia:** Transmission occurs via the feco-oral route through the ingestion of mature **cysts** in contaminated water or food. * **Entamoeba histolytica:** Transmission is feco-oral, specifically by ingesting the **quadrinucleate cyst** found in contaminated food/water or via flies/vectors. * **Ascaris lumbricoides:** Transmission is feco-oral through the ingestion of **embryonated eggs** from soil-contaminated hands or food. **NEET-PG High-Yield Pearls:** 1. **Skin Penetrators:** Remember the mnemonic **"ASH"** for parasites that infect via skin penetration: **A**nkylostoma duodenale (Hookworm), **S**trongyloides stercoralis, and **H**ookworm (*Necator americanus*). 2. **Autoinfection:** *Strongyloides* is unique because it can cause **internal autoinfection**, leading to "Hyperinfection Syndrome" in immunocompromised patients (especially those on steroids). 3. **Diagnostic Stage:** Unlike most helminths where eggs are found in stool, for *Strongyloides*, the **Rhabditiform larva** is the diagnostic stage found in stool samples.

Question 129: What is true about Trichomonas vaginalis?

A. Flagellated parasite
B. Fungal infection
C. Curdy white discharge
D. Pruritus (Correct Answer)

Explanation: **Explanation:** *Trichomonas vaginalis* is a flagellated protozoan that causes Trichomoniasis, one of the most common non-viral sexually transmitted infections (STIs) worldwide. **Why Option D is Correct:** **Pruritus (itching)** is a hallmark clinical feature of Trichomoniasis. The parasite causes significant inflammation of the vaginal and vulvar epithelium, leading to intense irritation, itching, and burning. While other symptoms like discharge are common, pruritus is a primary reason for patient presentation. **Analysis of Incorrect Options:** * **Option A (Flagellated parasite):** While *T. vaginalis* is indeed a flagellated protozoan, in the context of NEET-PG clinical questions, the focus is often on the **most characteristic clinical presentation**. While technically true, "Pruritus" is the specific clinical manifestation being tested here. (Note: In some exam patterns, if multiple options are factually correct, the most specific clinical sign is preferred). * **Option B (Fungal infection):** This is incorrect. *T. vaginalis* is a **protozoan**, not a fungus. Fungal vulvovaginitis is typically caused by *Candida albicans*. * **Option C (Curdy white discharge):** This is the classic description for **Vaginal Candidiasis**. In contrast, *Trichomonas* typically presents with a **profuse, frothy, yellowish-green, foul-smelling discharge**. **High-Yield Clinical Pearls for NEET-PG:** * **Strawberry Cervix:** Colpitis macularis (punctate hemorrhages on the cervix) is a pathognomonic sign. * **Diagnosis:** The gold standard is **NAAT**, but the most common bedside test is **Wet Mount microscopy** showing "jerky/twitching motility." * **pH:** Vaginal pH is typically **>4.5** (elevated). * **Treatment:** The drug of choice is **Metronidazole**. It is crucial to **treat the partner** simultaneously to prevent reinfection. * **Morphology:** It exists only in the **Trophozoite stage**; there is no cyst stage.

Question 130: Cysticercosis is caused by which of the following parasites?

A. Taenia solium (Correct Answer)
B. Taenia saginata
C. Ancylostoma duodenale
D. Echinococcus granulosus

Explanation: **Explanation:** **Cysticercosis** is a systemic parasitic infection caused by the larval stage (*Cysticercus cellulosae*) of the pork tapeworm, **Taenia solium**. 1. **Why Taenia solium is correct:** In the normal life cycle, humans are definitive hosts (harboring the adult worm) by eating undercooked pork containing cysticerci. However, if a human accidentally ingests **T. solium eggs** (via contaminated food/water or autoinfection), the human acts as an **accidental intermediate host**. The eggs hatch in the intestine, and oncospheres penetrate the gut wall to migrate to muscles, eyes, and the brain, forming cysticerci. **Neurocysticercosis** is the most common cause of acquired epilepsy worldwide. 2. **Why other options are incorrect:** * **Taenia saginata (Beef tapeworm):** Humans are only definitive hosts. Ingesting *T. saginata* eggs does **not** cause cysticercosis in humans because the eggs do not hatch in the human gut. * **Ancylostoma duodenale (Hookworm):** This is a nematode that causes iron-deficiency anemia; it does not form cysts in tissues. * **Echinococcus granulosus (Dog tapeworm):** This causes **Hydatid disease**, characterized by slow-growing unilocular cysts, typically in the liver or lungs. **High-Yield Clinical Pearls for NEET-PG:** * **Mode of Infection:** Cysticercosis is caused by ingesting **eggs**; Taeniasis (intestinal) is caused by ingesting **larvae** (cysticerci). * **Diagnosis:** MRI/CT shows "starry sky appearance" (multiple calcified cysts) or a cyst with a **scolex (dot sign)**. * **Treatment:** Albendazole is the drug of choice; steroids are added to manage inflammation from dying larvae.

Practice by Chapter

Classification of Parasites

Practice Questions

Intestinal Protozoa

Practice Questions

Blood and Tissue Protozoa

Practice Questions

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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