Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 691: Cyclodevelopmental type of transmission is seen in which of the following?

A. Malaria
B. Filaria (Correct Answer)
C. Plague
D. Cholera

Explanation: ### Explanation In medical entomology, the relationship between a parasite and its vector is classified based on whether the parasite multiplies or changes its form within the vector. **1. Why Filaria is Correct:** **Cyclodevelopmental transmission** occurs when the parasite undergoes **morphological changes** (developmental stages) within the vector but **does not multiply** in number. In Filariasis, the *Culex* mosquito ingests microfilariae, which develop into L1, L2, and finally infective L3 larvae. Throughout this process, one microfilaria results in only one L3 larva; no numerical increase occurs. **2. Analysis of Incorrect Options:** * **Malaria (Cyclo-propagative):** The parasite undergoes both developmental changes (gametocytes to sporozoites) and significant multiplication (sporogony). * **Plague (Propagative):** *Yersinia pestis* simply multiplies within the gut of the rat flea (*Xenopsylla cheopis*) without undergoing any change in form or life stage. * **Cholera (Mechanical):** This is a non-biological transmission. The housefly acts as a mechanical carrier, transporting *Vibrio cholerae* on its feet or proboscis without any biological interaction. **High-Yield Clinical Pearls for NEET-PG:** * **Propagative:** Multiplication only (e.g., Plague, Yellow Fever, Dengue). * **Cyclo-developmental:** Developmental change only (e.g., Filaria, Guinea worm). * **Cyclo-propagative:** Both change and multiplication (e.g., Malaria, Leishmaniasis, Sleeping Sickness). * **Transovarial Transmission:** Seen in Tick-borne diseases (e.g., Babesiosis, Rocky Mountain Spotted Fever) where the pathogen passes to the vector's offspring.

Question 692: Which one of the following is detected by the antigen detection test used for the diagnosis of P. falciparum malaria?

A. Circum-sporozoite protein
B. Merozoite surface antigen
C. Histidine-Rich-Protein I (HRP-I)
D. Histidine-Rich-Protein II (HRP-II) (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Histidine-Rich-Protein II (HRP-II)** Rapid Diagnostic Tests (RDTs) for malaria are immunochromatographic assays that detect specific parasite antigens in the blood. **Histidine-Rich Protein II (HRP-II)** is a water-soluble protein produced by the asexual stages and young gametocytes of ***Plasmodium falciparum***. It is the most common target for *P. falciparum*-specific RDTs because it is secreted in large quantities into the host's bloodstream. A key clinical feature of HRP-II is its persistence; it can remain detectable in the blood for 2–4 weeks even after successful parasite clearance, potentially leading to false-positive results in recently treated patients. **Analysis of Incorrect Options:** * **A. Circum-sporozoite protein:** This is the major surface protein of the sporozoite stage (the infective stage injected by mosquitoes). While it is a primary target for vaccine development (e.g., RTS,S/AS01), it is not used in routine diagnostic antigen detection tests. * **B. Merozoite surface antigen:** These proteins are involved in the attachment and invasion of RBCs by merozoites. Although immunogenic, they are not the standard biomarkers used in commercial RDT kits. * **C. Histidine-Rich-Protein I (HRP-I):** While *P. falciparum* produces several histidine-rich proteins, HRP-II is the specific isomer utilized for diagnostic sensitivity and standardized testing. **High-Yield Clinical Pearls for NEET-PG:** * **Pan-malarial markers:** To detect non-falciparum species (*P. vivax, P. ovale, P. malariae*), RDTs target **Parasite Lactate Dehydrogenase (pLDH)** or **Plasmodium Aldolase**. * **Prozone Effect:** Very high parasitemia can occasionally cause a false-negative RDT result due to the prozone phenomenon. * **Gene Deletion:** Emerging strains of *P. falciparum* with **pfhrp2/3 gene deletions** are a major public health concern as they cause HRP-II based RDTs to show false negatives.

Question 693: The Sabin-Feldman dye test is used for the diagnosis of which condition?

A. Toxoplasmosis (Correct Answer)
B. Syphilis
C. Herpes genitalis
D. Gardnerella vaginalis

Explanation: **Explanation:** The **Sabin-Feldman Dye Test** is the gold standard serological test for the diagnosis of **Toxoplasmosis**, caused by the protozoan *Toxoplasma gondii*. **1. Why Toxoplasmosis is correct:** The test is a neutralization assay based on the principle that live *Toxoplasma* tachyzoites are lysed in the presence of specific IgG antibodies and complement. * **Mechanism:** Normally, live tachyzoites take up **Methylene blue** dye and appear blue under a microscope. * **Positive Result:** If the patient’s serum contains anti-Toxoplasma antibodies, they bind to the tachyzoites and activate the complement system, causing membrane damage. Consequently, the tachyzoites lose their ability to take up the dye and appear **colorless/unstained**. **2. Why other options are incorrect:** * **Syphilis:** Diagnosed via Treponemal (TPHA, FTA-ABS) and Non-treponemal tests (VDRL, RPR). * **Herpes genitalis (HSV-2):** Diagnosed via Tzanck smear (showing multinucleated giant cells), PCR, or viral culture. * **Gardnerella vaginalis:** Diagnosed using **Amsel’s criteria**, which includes the presence of **Clue cells** on a saline wet mount and a positive Whiff test (KOH). **3. High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard:** While the Sabin-Feldman test is the reference standard, it is rarely used today because it requires live tachyzoites, posing a laboratory risk. ELISA is now the preferred screening method. * **Congenital Toxoplasmosis Triad:** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Treatment of Choice:** Pyrimethamine + Sulfadiazine (with Folinic acid to prevent bone marrow suppression). * **Alternative Test:** The **Indirect Fluorescent Antibody (IFA)** test is often used as it does not require live organisms.

Question 694: How is primary amoebic meningoencephalitis most likely acquired?

A. Diving or swimming in contaminated water (Correct Answer)
B. Intravenous drug abuse
C. Using human excrement as vegetable fertilizer
D. Eating raw fish or seafood

Explanation: **Explanation:** **Primary Amoebic Meningoencephalitis (PAM)** is caused by ***Naegleria fowleri***, often referred to as the "brain-eating amoeba." This free-living amoeba thrives in warm, stagnant freshwater (lakes, ponds, and poorly chlorinated swimming pools). 1. **Why Option A is correct:** The infection is acquired when water containing the amoebae is forcefully pushed into the nasal cavity, typically during **diving or swimming**. The amoebae penetrate the **nasal mucosa**, cross the **cribriform plate**, and migrate along the **olfactory nerves** to reach the brain. This leads to rapid, fulminant destruction of brain tissue and meningeal inflammation. 2. **Why other options are incorrect:** * **Option B:** IV drug abuse is associated with infections like HIV, Hepatitis B/C, or fungal endocarditis, but not PAM. * **Option C:** Using human excrement (night soil) as fertilizer is a common transmission route for soil-transmitted helminths (e.g., *Ascaris*) or feco-oral protozoa (e.g., *Entamoeba histolytica*), which cause intestinal or liver abscesses, not PAM. * **Option D:** Raw fish/seafood consumption is linked to parasites like *Diphyllobothrium latum* (fish tapeworm) or *Anisakis*, not *Naegleria*. **High-Yield Clinical Pearls for NEET-PG:** * **Pathogen:** *Naegleria fowleri* is a thermophilic amoeba (grows at temperatures up to 45°C). * **Diagnosis:** Look for **motile trophozoites** in a fresh wet mount of **CSF**. * **CSF Findings:** Resembles bacterial meningitis (high neutrophils, low glucose, high protein) but with RBCs (hemorrhagic). * **Treatment:** Drug of choice is **Amphotericin B**. * **Note:** Do not confuse PAM with **Granulomatous Amoebic Encephalitis (GAE)**, which is caused by *Acanthamoeba* or *Balamuthia* and typically occurs in immunocompromised patients via skin or respiratory routes.

Question 695: Which nematode resides in the caecum and appendix?

A. Ascaris lumbricoides
B. Mansonella ozzardi
C. Enterobius vermicularis (Correct Answer)
D. All of these

Explanation: **Explanation:** The correct answer is **Enterobius vermicularis** (Pinworm or Seatworm). **1. Why Enterobius vermicularis is correct:** The adult worms of *Enterobius vermicularis* primarily inhabit the **caecum, appendix, and adjacent portions of the ascending colon**. They attach to the mucosa using their mouth parts. A unique feature of their life cycle is that the gravid females migrate nocturnally through the anal canal to deposit eggs on the perianal skin, leading to the classic symptom of **pruritus ani**. **2. Why the other options are incorrect:** * **Ascaris lumbricoides (Roundworm):** The adult worms reside in the **lumen of the small intestine** (jejunum). While they can occasionally migrate into the appendix causing appendicitis, their primary habitat is not the caecum. * **Mansonella ozzardi:** This is a filarial nematode. The adult worms reside in the **mesentery, subperitoneal tissues, or thoracic cavity**, while the microfilariae circulate in the blood. They do not inhabit the intestinal lumen. **3. NEET-PG Clinical Pearls:** * **Diagnosis:** The "Gold Standard" is the **NIH Swab** or **Scotch Tape technique** performed early in the morning. Stool examination for eggs is usually negative (only 5% sensitivity) because eggs are laid on perianal skin, not in feces. * **Transmission:** Autoinfection and retroinfection are common. It is often a "familial infection." * **Drug of Choice:** Albendazole or Mebendazole (single dose, repeated after 2 weeks to kill newly hatched larvae). * **Ectopic sites:** In females, the worm can migrate into the vulva and vagina, causing vulvovaginitis or salpingitis.

Question 696: What are the major causative agents of Cutaneous larva migrans?

A. Ancylostoma braziliense (Correct Answer)
B. Brugia malayi
C. Loa loa
D. Wuchereria bancrofti

Explanation: **Explanation:** **Cutaneous Larva Migrans (CLM)**, also known as "creeping eruption," is a zoonotic infection caused by the larvae of animal hookworms. 1. **Why Option A is Correct:** **Ancylostoma braziliense** (the cat hookworm) is the most common cause of CLM. Humans are accidental hosts; when larvae in soil (contaminated by animal feces) penetrate human skin, they find themselves in an unnatural host. Because they lack the enzymes necessary to penetrate the deeper dermis and enter the bloodstream, they remain trapped in the epidermis. They migrate aimlessly, creating the characteristic **serpiginous, erythematous, and intensely pruritic tracks.** 2. **Why the Other Options are Incorrect:** * **Brugia malayi & Wuchereria bancrofti (Options B & D):** These are the causative agents of **Lymphatic Filariasis**. They are transmitted by mosquito bites and reside in the lymphatic system, leading to elephantiasis, not cutaneous migratory tracks. * **Loa loa (Option C):** This causes **Loiasis** (African eye worm). While it involves migration, it presents as transient **Calabar swellings** (localized angioedema) or the visible migration of the adult worm across the subconjunctiva of the eye. **High-Yield NEET-PG Pearls:** * **Other causes of CLM:** *Ancylostoma caninum* (dog hookworm). * **Larva Currens:** Often confused with CLM, this is caused by ***Strongyloides stercoralis***. It is much faster (moving 5–10 cm/hr vs. CLM’s 1–2 cm/day) and typically occurs in the perianal region. * **Treatment of choice:** Topical or oral **Albendazole** or **Ivermectin**. * **Diagnosis:** Primarily clinical; biopsy is usually not recommended as the larva is often ahead of the visible track.

Question 697: All of the following are intracellular parasites, except?

A. Leishmania
B. Plasmodium
C. Toxoplasma
D. None of these (Correct Answer)

Explanation: **Explanation:** The correct answer is **None of these** because all three organisms listed (Leishmania, Plasmodium, and Toxoplasma) are obligate or facultative intracellular parasites during their life cycles in the human host. **1. Why "None of these" is correct:** In medical parasitology, parasites are classified based on their habitat. Intracellular parasites must enter host cells to survive, evade the immune system, or replicate. Since A, B, and C are all intracellular, the statement "except" applies to none of them. **2. Analysis of Options:** * **Leishmania (Option A):** These are **obligate intracellular** protozoa. In humans, the *amastigote* form resides and multiplies exclusively within the phagolysosomes of **macrophages** (Reticuloendothelial system). * **Plasmodium (Option B):** The causative agents of malaria are intracellular parasites. They replicate first in **hepatocytes** (exo-erythrocytic schizogony) and subsequently in **erythrocytes** (erythrocytic schizogony). * **Toxoplasma gondii (Option C):** This is an **obligate intracellular** coccidian parasite. It can infect almost any nucleated cell in the body, typically residing within a "parasitophorous vacuole" to avoid lysosomal fusion. **Clinical Pearls for NEET-PG:** * **Leishmania:** Look for "LD bodies" (amastigotes) in bone marrow or splenic aspirates. * **Plasmodium:** *P. falciparum* is unique because it causes infected RBCs to develop "knobs," leading to sequestration in capillaries (cytoadherence). * **Toxoplasma:** Classic triad of Congenital Toxoplasmosis: Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Other Intracellular Parasites:** *Trypanosoma cruzi* (amastigote stage), *Babesia*, and *Cryptosporidium*.

Question 698: A man working in a construction company presented with watery, foul-smelling diarrhea since 3 weeks. There is no blood in the stools. If giardiasis is suspected, what is the best diagnostic method?

A. Complement fixation test (CFT)
B. Presence of both cysts and trophozoites in stools (Correct Answer)
C. Presence of cysts only
D. Haemagglutination

Explanation: ### Explanation **Correct Answer: B. Presence of both cysts and trophozoites in stools** **Medical Concept:** *Giardia lamblia* (also known as *G. duodenalis* or *G. intestinalis*) is a flagellated protozoan that colonizes the upper small intestine. In a patient with symptomatic giardiasis (watery, foul-smelling, fatty diarrhea), the diagnosis is primarily established by **stool microscopy**. * **Cysts** are the infective and resistant forms typically found in formed or semi-formed stools. * **Trophozoites** (the pear-shaped, "monkey-face" active forms) are found in loose or diarrheic stools due to rapid transit time. Finding both stages in a stool sample provides the highest diagnostic yield for routine microscopy. **Why Other Options are Incorrect:** * **Option C (Cysts only):** While cysts are common, excluding trophozoites reduces the sensitivity of the stool examination, especially in acute diarrheal phases where trophozoites are frequently shed. * **Options A & D (CFT and Haemagglutination):** These are serological tests. Serology is generally **not useful** for Giardia because the parasite is intraluminal and non-invasive; it does not typically elicit a significant systemic antibody response that can distinguish between past and current infection. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Characterized by "Steatorrhea" (fatty, foul-smelling stools that float) and malabsorption. It does **not** cause blood in stools (non-invasive). * **Stool Pattern:** Cysts are shed intermittently. Therefore, at least **three consecutive stool samples** should be examined to rule out infection. * **String Test (Entero-test):** Used if stool microscopy is negative but suspicion remains high; it samples duodenal fluid. * **Morphology:** Trophozoites have a characteristic "falling leaf" motility and a "monkey-face" appearance (two nuclei and four pairs of flagella). * **Treatment:** Drug of choice is **Tinidazole** (single dose) or Metronidazole.

Question 699: Which parasite commonly causes pulmonary eosinophilia syndrome?

A. Strongyloides (Correct Answer)
B. Enterobiasis
C. Hookworm
D. Trichinella

Explanation: **Explanation:** The correct answer is **Strongyloides stercoralis**. Pulmonary eosinophilia (often manifesting as Loeffler’s syndrome) occurs during the **hepatopulmonary phase** of larval migration. When larvae penetrate the skin and travel via the bloodstream to the lungs, they break into the alveoli, causing an inflammatory response characterized by cough, dyspnea, and a significant rise in peripheral blood eosinophils. **Why Strongyloides is the best fit:** While several helminths migrate through the lungs, *Strongyloides stercoralis* is unique due to its **autoinfection cycle**. This allows the parasite to persist for decades and causes recurrent bouts of pulmonary symptoms and chronic eosinophilia. In immunocompromised patients, this can escalate into "Hyperinfection Syndrome," leading to severe pulmonary hemorrhage and secondary bacterial pneumonia. **Analysis of Incorrect Options:** * **Enterobiasis (Pinworm):** This parasite does not have a tissue migratory phase. The life cycle is limited to the gastrointestinal tract; therefore, it does not cause pulmonary symptoms or significant systemic eosinophilia. * **Hookworm:** While *Ancylostoma duodenale* and *Necator americanus* do undergo pulmonary migration, they are less commonly associated with persistent pulmonary eosinophilia compared to *Strongyloides*. Their primary clinical manifestation is iron-deficiency anemia. * **Trichinella spiralis:** This parasite causes marked systemic eosinophilia, but its larvae migrate to and encyst in **striated muscle**, not the lungs. Clinical features include periorbital edema and myalgia. **High-Yield NEET-PG Pearls:** * **Loeffler’s Syndrome:** Classically caused by *Ascaris lumbricoides* (most common), *Strongyloides*, and Hookworms (mnemonic: **NAS** - *Necator, Ascaris, Strongyloides*). * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to microfilariae (*Wuchereria bancrofti*); characterized by nocturnal cough and extremely high IgE levels. * **Strongyloides Diagnosis:** Look for **rhabditiform larvae** in the stool (eggs are rarely seen).

Question 700: Leishmania is cultured in which medium?

A. Chocolate agar
B. NNN (Correct Answer)
C. Tellurite
D. Sabouraud's agar

Explanation: **Explanation:** **1. Why NNN Medium is Correct:** *Leishmania* species (the causative agents of Kala-azar and Cutaneous Leishmaniasis) are traditionally cultured in **NNN (Novy-MacNeal-Nicolle) medium**. This is a specialized **biphasic medium** consisting of a solid phase (blood agar made with rabbit blood) and a liquid phase (overlay of saline or broth). In this medium, the parasite transforms from the amastigote form (found in humans) into the **flagellated promastigote form**, which multiplies in the liquid phase. **2. Why Other Options are Incorrect:** * **Chocolate Agar:** This is an enriched medium used for fastidious bacteria like *Haemophilus influenzae* and *Neisseria meningitidis*. It is essentially blood agar where the red cells have been lysed by heat. * **Tellurite (Potassium Tellurite Agar):** This is a selective medium used for **Corynebacterium diphtheriae**. The bacteria reduce tellurite to metallic tellurium, resulting in characteristic black-colored colonies. * **Sabouraud’s Dextrose Agar (SDA):** This is the standard medium used for the cultivation of **Fungi** (molds and yeasts). Its low pH inhibits bacterial growth. **3. High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Diagnosis:** While NNN culture is highly specific, the gold standard for Kala-azar diagnosis remains the demonstration of **LD bodies (Amastigotes)** in splenic or bone marrow aspirates. * **Other Media for Leishmania:** Apart from NNN, **Schneider’s Drosophila medium** (liquid medium) is also used. * **Vector:** *Leishmania donovani* is transmitted by the bite of the female **Sandfly (*Phlebotomus argentipes*)**. * **Drug of Choice:** Liposomal Amphotericin B is currently the preferred treatment for Visceral Leishmaniasis.

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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