Parasitology — MCQs

Parasitology Indian Medical PG Practice Questions and MCQs

Question 171: Which of the following acts as an intermediate host for hydatid disease?

A. Man (Correct Answer)
B. Dog
C. Cat
D. Foxes

Explanation: **Explanation:** Hydatid disease is caused by the larval stage of the cestode **_Echinococcus granulosus_** (Dog tapeworm). Understanding the life cycle is crucial for NEET-PG: 1. **Why Man is the Correct Answer:** In the life cycle of *E. granulosus*, the **Intermediate Host** is the one that harbors the larval stage (hydatid cyst). Naturally, this role is played by sheep and cattle. However, **Humans** act as **accidental intermediate hosts** when they ingest eggs (oncospheres) via contaminated food or water. In humans, the cycle ends (dead-end host) because the larvae cannot be transmitted back to the definitive host. 2. **Why Other Options are Incorrect:** * **B. Dog:** The dog is the **Definitive Host**. It harbors the adult tapeworm in its intestine and passes eggs in its feces. * **D. Foxes:** Along with wolves and jackals, foxes act as definitive hosts for *E. granulosus* or *E. multilocularis*. * **C. Cat:** Cats are generally not involved in the transmission cycle of *E. granulosus*. **High-Yield Clinical Pearls for NEET-PG:** * **Infective Form for Man:** Eggs (Oncospheres) found in dog feces. * **Most Common Site:** Liver (Right lobe), followed by the Lungs. * **Diagnosis:** Casoni’s test (immediate hypersensitivity, now largely replaced), USG (Gharbi’s classification), and "Water Lily sign" on imaging. * **Management:** PAIR (Puncture, Aspiration, Injection, Re-aspiration) and Albendazole. * **Microscopy:** Look for "Hydatid sand" (brood capsules and protoscolices).

Question 172: Ova in the stool are not of diagnostic significance in which of the following parasitic infections?

A. Strongyloides (Correct Answer)
B. Enterobius
C. Trichuris
D. Ankylostoma

Explanation: **Explanation:** The correct answer is **Strongyloides stercoralis**. The primary diagnostic stage found in the stool for this parasite is the **Rhabditiform larva**, not the egg (ova). **1. Why Strongyloides is correct:** In *Strongyloides stercoralis* infections, the adult female lives in the mucosal epithelium of the small intestine. She lays eggs that hatch almost immediately within the intestinal mucosa. Therefore, by the time the parasite reaches the stool, it is already in the **L1 (Rhabditiform) larval stage**. Finding eggs in the stool is extremely rare and usually only occurs in cases of severe purgation. **2. Why the other options are incorrect:** * **Trichuris trichiura (Whipworm):** Diagnosis is confirmed by identifying characteristic **barrel-shaped eggs** with bipolar plugs in the stool. * **Ankylostoma duodenale (Hookworm):** Diagnosis relies on finding **oval, segmented, thin-shelled eggs** (usually at the 4-8 cell stage) in the feces. * **Enterobius vermicularis (Pinworm):** While the **NIH swab or Scotch tape test** is the gold standard (detecting eggs on the perianal skin), the eggs are the definitive diagnostic stage. Although rarely seen in routine stool samples, they remain the diagnostic unit of the parasite. **NEET-PG High-Yield Pearls:** * **Strongyloides:** Unique for its **autoinfection** cycle and the ability to cause **Hyperinfection Syndrome** in immunocompromised patients (e.g., those on steroids). * **Larva Currens:** A rapidly moving serpiginous cutaneous eruption pathognomonic for Strongyloidiasis. * **Stool Examination:** If larvae are not found in routine stool, the **Baermann technique** or **Agar plate culture** can be used to increase sensitivity.

Question 173: Fasciolopsis hepatica is also known as:

A. Intestinal fluke
B. Garrison's fluke
C. Lane's fluke
D. Liver fluke (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. Liver fluke**. *Fasciola hepatica* (commonly confused with *Fasciolopsis buski*) is a major trematode that primarily inhabits the **bile ducts** of the liver in humans and herbivorous animals (sheep and cattle). It is clinically significant as the causative agent of **Fascioliasis**. Humans typically acquire the infection by ingesting metacercariae encysted on aquatic plants, such as watercress. **Analysis of Options:** * **A. Intestinal fluke:** This refers to ***Fasciolopsis buski***. It is the largest fluke infecting humans but resides in the duodenum and jejunum, not the liver. * **B. Garrison's fluke:** This is the common name for ***Echinostoma ilocanum***, a small intestinal fluke prevalent in Southeast Asia (particularly the Philippines). * **C. Lane's fluke:** This is a historical synonym for ***Artyfechinostomum sufrartyfex***, another rare intestinal echinostome. **High-Yield Clinical Pearls for NEET-PG:** * **Intermediate Hosts:** 1st intermediate host is the snail (*Lymnaea* species); 2nd intermediate hosts are aquatic plants. * **Clinical Presentation:** Presents with a triad of fever, hepatomegaly, and marked **eosinophilia**. Chronic infection leads to biliary colic, jaundice, and "Halzoun" (pharyngeal fascioliasis from eating raw infected liver). * **Diagnosis:** Detection of large, operculated, unembryonated eggs in stool or bile. * **Drug of Choice:** Unlike most flukes (where Praziquantel is used), the DOC for *Fasciola hepatica* is **Triclabendazole**.

Question 174: Congenital toxoplasmosis is characterized by which of the following statements?

A. IgA is better than IgM in detection
B. Diagnosis is made by the detection of IgM in cord blood
C. IgG is diagnostic (Correct Answer)
D. It is not recalled

Explanation: **Explanation:** **Congenital Toxoplasmosis** occurs due to the transplacental transmission of *Toxoplasma gondii* during a primary maternal infection. **Why IgG is Diagnostic:** In the context of this specific question, the detection of **IgG** is a cornerstone of diagnosis, particularly when assessing maternal status and long-term infant monitoring. While maternal IgG crosses the placenta, a **persistent or rising titer of IgG** in the infant over the first year of life (beyond the point where maternal antibodies should wane) is definitive for congenital infection. Furthermore, the **Sabin-Feldman Dye Test**, which measures IgG, remains the "Gold Standard" reference for toxoplasmosis serology. **Analysis of Incorrect Options:** * **Option B (IgM in cord blood):** While IgM is produced by the fetus and does not cross the placenta, cord blood is often contaminated with maternal blood, leading to **false positives**. Therefore, testing the infant’s peripheral blood after birth is preferred over cord blood. * **Option A (IgA vs. IgM):** IgM is generally the first-line screening antibody for acute neonatal infection. While IgA ELISA can be more sensitive than IgM in some neonatal cases, it is not universally "better" or the primary diagnostic standard compared to the established role of IgG/IgM. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Triad (Sabin’s Triad):** Chorioretinitis, Hydrocephalus, and Intracranial calcifications (typically diffuse). * **Transmission Risk:** The risk of transmission increases with gestational age (highest in the 3rd trimester), but the **severity** of fetal damage is highest if infected in the 1st trimester. * **Treatment:** The standard regimen is **Pyrimethamine, Sulfadiazine, and Folinic acid** (Leucovorin). * **Diagnosis in Pregnancy:** Spiramycin is used to prevent transmission if the mother is infected but the fetus is not yet affected.

Question 175: Which of the following tests does NOT help in the laboratory diagnosis of Kala-azar?

A. Bone marrow examination
B. Immobilization test (Correct Answer)
C. Blood smear examination
D. Aldehyde test

Explanation: **Explanation:** Kala-azar (Visceral Leishmaniasis), caused by *Leishmania donovani*, is diagnosed through direct parasite visualization, serology, or non-specific biochemical tests. **Why "Immobilization Test" is the correct answer:** The **TPI (Treponema Pallidum Immobilization) test** is a highly specific historical test used for the diagnosis of **Syphilis**, not Kala-azar. It involves observing the loss of motility of *T. pallidum* in the presence of patient antibodies. It has no application in leishmaniasis. **Analysis of Incorrect Options:** * **Bone Marrow Examination:** This is the **gold standard** for diagnosis. Aspiration (usually from the sternum or iliac crest) reveals the **Amastigote forms** (LD bodies) within macrophages. It is safer than splenic aspiration. * **Blood Smear Examination:** While less sensitive than bone marrow, a thick or thin peripheral blood smear can demonstrate LD bodies within monocytes or neutrophils, especially in heavy infections. * **Aldehyde Test (Napier’s Test):** This is a non-specific biochemical test based on **hypergammaglobulinemia**. When formalin is added to the patient's serum, it turns opaque and solidifies (like the white of a boiled egg). It becomes positive only after 3 months of infection. **High-Yield Clinical Pearls for NEET-PG:** 1. **Splenic Aspiration:** Most sensitive (95%+) but carries a risk of hemorrhage; Bone marrow is the preferred routine diagnostic. 2. **rK39 Immunochromatographic Test:** The rapid diagnostic test of choice for field use (high sensitivity and specificity). 3. **Culture Medium:** NNN (Novy-MacNeal-Nicolle) medium is used to grow the **Promastigote** form. 4. **Montenegro (Leishmanin) Skin Test:** It is **negative** in active Kala-azar and becomes positive only after recovery (delayed hypersensitivity).

Question 176: All of the following are spread by autoinfection except?

A. Taenia solium
B. Strongyloides stercoralis
C. Hymenolepis nana
D. Ascaris lumbricoides (Correct Answer)

Explanation: **Explanation:** The concept of **autoinfection** refers to a process where an individual serves as both the reservoir and the host, re-infecting themselves without the parasite needing to undergo a mandatory developmental cycle in the external environment. **Why Ascaris lumbricoides is the correct answer:** *Ascaris lumbricoides* (Giant Roundworm) **cannot** cause autoinfection. The eggs passed in the feces are unembryonated and non-infective. They require a period of 2–3 weeks in the soil to become embryonated (infective stage). Since the eggs are not immediately infective upon excretion, direct person-to-person or self-infection is biologically impossible. **Why the other options are incorrect:** * **Taenia solium (Pork Tapeworm):** Can cause **internal autoinfection** if gravid proglottids are regurgitated into the stomach or **external autoinfection** via the feco-oral route (leading to Cysticercosis). * **Strongyloides stercoralis:** Known for **internal autoinfection**, where rhabditiform larvae transform into filariform (infective) larvae within the host's intestine, penetrating the perianal skin or intestinal mucosa. This can lead to life-threatening hyperinfection syndrome. * **Hymenolepis nana (Dwarf Tapeworm):** The only cestode that completes its life cycle in a single host. Eggs can hatch within the intestine, leading to **internal autoinfection**. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Autoinfection:** "**S**top **H**is **E**ntire **T**aenia" (**S**trongyloides, **H**ymenolepis nana, **E**nterobius vermicularis, **T**aenia solium). * *Enterobius vermicularis* (Pinworm) causes autoinfection via the **retro-infection** route or finger-to-mouth transfer due to perianal itching. * *Cryptosporidium parvum* is a protozoan that also exhibits autoinfection via thin-walled oocysts.

Question 177: Which is a Plasmodium falciparum vaccine strain?

A. RTS, S/AS01 (Correct Answer)
B. RTS, RS
C. Spfl6
D. NYVAC-PF01

Explanation: **Explanation:** **RTS,S/AS01 (Mosquirix)** is the first malaria vaccine to receive WHO recommendation for widespread use in children. It is a recombinant protein vaccine that targets the **circumsporozoite protein (CSP)** of *Plasmodium falciparum*. * **Mechanism:** It induces antibodies and T-cells to prevent the parasite from infecting the liver (pre-erythrocytic stage). * **Composition:** The "RTS" refers to the repeat (R) and T-cell epitope (T) regions of the CSP fused to the Hepatitis B surface antigen (S). "AS01" is the chemical adjuvant system used to enhance the immune response. **Analysis of Incorrect Options:** * **RTS, RS:** This is a distractor; no such nomenclature exists for a validated malaria vaccine. * **Spf66:** Developed by Manuel Patarroyo, this was a synthetic peptide vaccine. While historically significant as one of the first candidates tested in field trials, it showed low efficacy and is not currently used. * **NYVAC-Pf7:** This was an early multi-antigen DNA vaccine candidate using a poxvirus vector. It failed to show significant protection in clinical trials. **High-Yield Clinical Pearls for NEET-PG:** * **R21/Matrix-M:** The second malaria vaccine recently recommended by the WHO (2023). It is highly effective and easier to manufacture than RTS,S. * **Target Stage:** Both RTS,S and R21 target the **pre-erythrocytic (sporozoite) stage** to prevent the blood-stage infection that causes clinical symptoms. * **Species Specificity:** These vaccines are specific to ***P. falciparum*** and do not protect against *P. vivax*. * **Dosing:** RTS,S requires a 4-dose schedule in children starting from 5 months of age.

Question 178: The egg of which helminth can be concentrated in a saturated salt solution?

A. Taenia saginata
B. Taenia solium
C. Unfertilized egg of Ascaris
D. Ancylostoma duodenale (Correct Answer)

Explanation: **Explanation:** The concentration of eggs in a stool sample depends on the principle of **Specific Gravity**. In the **Saturated Salt Floatation Technique** (using a saturated solution of NaCl with a specific gravity of approximately 1.200), eggs that have a lower specific gravity than the solution will float to the surface and can be collected. **Why Ancylostoma duodenale is correct:** The eggs of Hookworms (*Ancylostoma duodenale* and *Necator americanus*) have a relatively low specific gravity (approx. 1.055). Since this is significantly lower than that of saturated salt solution (1.200), the eggs float effectively, making this a standard method for their concentration. **Why the other options are incorrect:** * **Unfertilized eggs of Ascaris lumbricoides:** These are the heaviest helminthic eggs. Due to their high specific gravity (approx. 1.130) and the presence of a heavy, mammillated albuminous coat, they are too heavy to float in saturated salt solution and typically sink. (Note: Fertilized eggs *can* float). * **Taenia saginata and Taenia solium:** The eggs of *Taenia* species are relatively heavy (specific gravity approx. 1.100). While they may occasionally float, the technique is unreliable for them. They are better concentrated using sedimentation methods. **High-Yield NEET-PG Pearls:** * **Floaters (Light eggs):** Hookworm, *Ascaris* (Fertilized), *Enterobius vermicularis*, and *Hymenolepis nana*. * **Sinkers (Heavy eggs):** Unfertilized *Ascaris* eggs, *Taenia* spp., and all operculated eggs (e.g., *Fasciola*, *Diphyllobothrium*). * **Modified Floatation:** For heavier eggs like *Taenia*, a solution with higher specific gravity (e.g., Zinc Sulfate, sp. gr. 1.180–1.200) is used. * **Formal-Ether Sedimentation:** This is the preferred "gold standard" for concentrating almost all types of eggs and cysts, including those that sink.

Question 179: Schistosoma is transmitted by which of the following?

A. Cyclops
B. Fish
C. Snail (Correct Answer)
D. Cattle

Explanation: **Explanation:** **Schistosoma** (Blood Flukes) are unique trematodes that cause Schistosomiasis. The correct answer is **Snail** because all trematodes (flukes) require a specific freshwater snail as their **obligate intermediate host** to complete their life cycle. 1. **Why Snail is Correct:** In the life cycle, eggs excreted in human feces or urine hatch into **miracidia** upon reaching water. These miracidia must infect a specific snail (e.g., *Biomphalaria* for *S. mansoni*, *Bulinus* for *S. haematobium*). Inside the snail, they undergo asexual reproduction to emerge as **Cercariae**, which are the infective stage for humans. Infection occurs via direct **skin penetration** while wading in contaminated water. 2. **Why other options are incorrect:** * **Cyclops:** This is the intermediate host for *Dracunculus medinensis* (Guinea worm), *Diphyllobothrium latum* (Fish tapeworm), and *Gnathostoma spinigerum*. * **Fish:** Freshwater fish act as the second intermediate host for *Clonorchis sinensis* (Chinese liver fluke) and *Opisthorchis*, but not for Schistosoma. * **Cattle:** Cattle serve as the intermediate host for *Taenia saginata* (Beef tapeworm). **High-Yield Clinical Pearls for NEET-PG:** * **Infective stage:** Cercaria (specifically fork-tailed cercaria). * **Diagnostic stage:** Non-operculated eggs with spines (e.g., *S. haematobium* has a **terminal spine**). * **Unique feature:** Unlike other flukes, Schistosomes are **dioecious** (separate sexes) and do not have a redia stage in their life cycle. * **Clinical association:** *S. haematobium* is strongly linked to **Squamous Cell Carcinoma of the bladder**. * **Drug of Choice:** Praziquantel.

Question 180: What is the common name for Echinococcus granulosus?

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

Explanation: **Explanation:** The question asks for the common name of *Echinococcus granulosus*. However, based on the provided answer key, there is a discrepancy: **Hymenolepis nana** is the common name for the **Dwarf Tapeworm**, not *Echinococcus granulosus*. The common name for ***Echinococcus granulosus*** is the **Hydatid Tapeworm** or Dog Tapeworm. Assuming the question intends to test the identification of common names for major helminths: 1. **Hymenolepis nana (Correct per key):** Known as the **Dwarf Tapeworm**, it is the smallest intestinal cestode infecting humans. It is unique because it does not require an intermediate host (direct life cycle) and is the most common cause of all cestode infections worldwide. 2. **Echinococcus granulosus (Option A):** Known as the **Hydatid Tapeworm**. It causes Cystic Echinococcosis (Hydatid disease), typically presenting as slow-growing cysts in the liver or lungs. 3. **Loa loa (Option B):** Known as the **African Eye Worm**. It is a nematode transmitted by the *Chrysops* (deer fly) and is famous for causing "Calabar swellings" and migrating across the subconjunctiva of the eye. 4. **Schistosoma mansoni (Option D):** Known as **Manson’s Blood Fluke**. It resides in the mesenteric veins and is a major cause of intestinal schistosomiasis and portal hypertension. **NEET-PG Clinical Pearls:** * **H. nana:** Only tapeworm that can complete its entire life cycle in a single host (Human). * **E. granulosus:** Diagnosis involves the "Casoni skin test" (historical) and imaging showing "water lily sign" or "hydatid sand." * **Treatment:** Albendazole is the drug of choice for *Echinococcus*, while Praziquantel is used for *H. nana* and *Schistosoma*.

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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