Parasitology Practice Questions

Q: What is a definitive host?

One in which sexual multiplication takes place. In parasitology, hosts are classified based on the stage of the parasite’s life cycle they support. **Correct Answer: A. One in which sexual multiplication takes place** The **definitive host** (or final host) is defined as the host in which the parasite reaches **sexual maturity** and undergoes **sexual reproduction**. For example, in the life cycle of *Plasmodium* (malaria), the female *Anopheles* mosquito is the definitive host because the sexual phase (sporogony) occurs within it. In most helminthic infections, humans serve as the definitive host. **Explanation of Incorrect Options:** * **B. One in which asexual multiplication takes place:** This defines the **Intermediate Host**. In malaria, humans are the intermediate host because the parasite undergoes asexual multiplication (schizogony) in the liver and RBCs. * **C. One that harbors the adult form:** While the definitive host often harbors the adult form, this is not the primary biological definition. The defining characteristic is the occurrence of the sexual cycle. * **D. One that harbors the larval form:** This is characteristic of an **Intermediate Host**, which harbors the larval or asexual stages of the parasite. **High-Yield Clinical Pearls for NEET-PG:** * **Accidental Host:** A host that is not required for the parasite's maintenance but becomes infected (e.g., humans in *Echinococcus granulosus*). * **Paratenic Host:** A "transport" host where the parasite survives but undergoes **no development**. * **Reservoir Host:** An animal host that maintains the parasite in nature and serves as a source of infection to humans. * **Exception to Remember:** In *Taenia solium*, humans are the definitive host (harboring the adult worm), but if humans ingest the eggs, they can act as an intermediate host (developing Cysticercosis).

Q: Which of the following are NOT seen in the peripheral smear in Plasmodium falciparum infection?

Maurer's dots and Schizonts. In *Plasmodium falciparum* infection, the peripheral blood smear typically shows only **early trophozoites (ring forms)** and **gametocytes**. ### Why the Correct Answer is Right **Maurer’s dots and Schizonts** are generally absent from the peripheral circulation in *P. falciparum*: 1. **Schizonts:** *P. falciparum* exhibits a phenomenon called **sequestration**. Mature stages (late trophozoites and schizonts) express PfEMP-1 proteins on the RBC surface, causing them to adhere to the endothelial lining of deep capillary beds (brain, kidneys, etc.). Therefore, they are rarely seen in peripheral blood unless the infection is extremely heavy or terminal. 2. **Maurer’s dots:** These are coarse granulations seen in the cytoplasm of infected RBCs. While they are characteristic of *P. falciparum*, they are usually only visible in the mature stages that have been sequestered, making them an uncommon finding in a standard peripheral smear. ### Analysis of Other Options * **Accolé (Appliqué) forms:** These are early ring forms found at the very edge of the RBC. They are a hallmark of *P. falciparum* and are **frequently seen** in peripheral smears. * **Schuffner’s dots:** These are characteristic of *P. vivax* and *P. ovale*, not *P. falciparum*. ### NEET-PG High-Yield Pearls * **Multiple rings per RBC** and **Accolé forms** are diagnostic of *P. falciparum*. * **Gametocytes:** *P. falciparum* gametocytes are uniquely **crescent or banana-shaped**. * **Sequestration** is the primary reason why *P. falciparum* causes **Cerebral Malaria** (cytoadherence in brain capillaries). * **Ziemann’s dots** are associated with *P. malariae*.

Q: Auto infection occurs in which of the following organisms?

All of the above. **Explanation:** **Autoinfection** is a process where an individual serves as both the reservoir and the host, becoming reinfected by a pathogen already present in their body without the need for an external environment or intermediate host. * **Hymenolepis nana (Dwarf Tapeworm):** This is the most common cause of autoinfection. Eggs released in the intestine can hatch immediately into oncospheres, which penetrate the villi and develop into cysticercoid larvae, eventually maturing into adult worms within the same host (**Internal Autoinfection**). * **Enterobius vermicularis (Pinworm):** Eggs deposited on the perianal skin can hatch into larvae that migrate back into the anus (**Retroinfection**) or be transferred to the mouth via contaminated fingers (**External Autoinfection/Fecal-oral**). * **Taenia solium (Pork Tapeworm):** If a person harboring the adult worm ingests eggs (via contaminated food or reverse peristalsis), the eggs hatch into larvae that migrate to tissues, causing **Cysticercosis**. This is a critical clinical distinction from T. saginata, which does not cause autoinfection. **High-Yield NEET-PG Pearls:** 1. **Other organisms causing autoinfection:** *Strongyloides stercoralis* (Internal autoinfection via filariform larvae) and *Cryptosporidium parvum*. 2. **H. nana** is unique because it is the only cestode that does not mandatory require an intermediate host. 3. **Hyperinfection syndrome:** Seen in *Strongyloides* in immunocompromised patients (e.g., those on steroids) due to massive internal autoinfection. 4. **Diagnosis:** *Enterobius* is best diagnosed via the **NIH Swab/Scotch Tape test**, not routine stool microscopy.

Q: Which organism's filariform larva is infective?

Necator americanus. **Explanation:** The correct answer is **Necator americanus**. In the life cycle of hookworms (*Necator americanus* and *Ancylostoma duodenale*), the eggs hatch in the soil into rhabditiform larvae, which then transform into non-feeding, highly motile **filariform larvae (L3 stage)**. This filariform larva is the infective stage that penetrates human skin (usually the feet) to cause infection. **Analysis of Options:** * **Necator americanus (Hookworm):** Infective stage is the **filariform larva** (skin penetration). *Strongyloides stercoralis* also shares this infective stage. * **Enterobius vermicularis (Pinworm):** Infective stage is the **embryonated egg** containing a larva, typically acquired via ingestion (autoinoculation or fomites). * **Ascaris lumbricoides (Roundworm):** Infective stage is the **embryonated egg** (containing L2 larva) acquired via ingestion of contaminated food or water. * **Trichuris trichura (Whipworm):** Infective stage is the **embryonated egg** acquired via the feco-oral route. **High-Yield NEET-PG Pearls:** 1. **Skin Penetrators:** Remember the mnemonic **"S-A-N-D"** for organisms that penetrate the skin: ***S**trongyloides*, ***A**ncylostoma*, ***N**ecator*, and ***D**ermatobia*. 2. **Lung Migration:** Hookworms, *Ascaris*, and *Strongyloides* all exhibit a heart-lung migration phase, which can lead to **Loeffler’s syndrome** (eosinophilic pneumonia). 3. **Hookworm Clinical Feature:** Chronic infection leads to **Iron Deficiency Anemia** due to blood-sucking by adult worms in the small intestine. 4. **Diagnostic Stage:** For hookworms, the diagnostic stage is the **non-bile stained, segmented egg** in stool.

Q: The Sabin Feldman dye test is used for the diagnosis of which of the following conditions?

Toxoplasmosis. **Explanation:** The **Sabin-Feldman Dye Test (SFDT)** is the gold standard serological test for the diagnosis of **Toxoplasmosis**, caused by the protozoan *Toxoplasma gondii*. **Mechanism:** The test is based on the principle that specific antibodies present in the patient's serum will bind to live *Toxoplasma* tachyzoites. When these antibody-bound tachyzoites are exposed to **complement** (the "accessory factor") and **methylene blue dye**, the antibodies prevent the dye from entering the organism. * **Positive result:** Tachyzoites remain **unstained** (colorless) because they have been neutralized by antibodies. * **Negative result:** Tachyzoites take up the dye and appear **blue** (indicating no antibodies are present). **Analysis of Incorrect Options:** * **Trypanosomiasis:** Diagnosed via peripheral blood smears (African) or CATT (Card Agglutination Test for Trypanosomiasis). * **Kala-azar (Visceral Leishmaniasis):** The classic screening test is the **rK39 antigen strip test** or the Aldehyde test of Napier. * **Yellow Fever:** Being a viral hemorrhagic fever, it is diagnosed via IgM ELISA or PCR, not dye exclusion tests. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard:** SFDT is highly sensitive and specific but rarely performed now due to the requirement of live tachyzoites (biohazard risk). * **Toxoplasmosis Triad (Congenital):** Chorioretinitis, Hydrocephalus, and Intracranial calcifications. * **Drug of Choice:** Pyrimethamine + Sulfadiazine. * **Alternative Diagnosis:** PCR is preferred for congenital toxoplasmosis (amniotic fluid) and immunocompromised patients.

Q: Which drug is NOT used in the treatment of visceral leishmaniasis?

Hydroxychloroquine. **Explanation:** Visceral Leishmaniasis (Kala-azar), caused by *Leishmania donovani*, requires specific antiprotozoal therapy. **Hydroxychloroquine (Option D)** is the correct answer because it is an antimalarial and immunomodulatory drug (used in SLE and Rheumatoid Arthritis) with no clinical efficacy against *Leishmania* species. **Analysis of Options:** * **Stibogluconate (Option A):** A pentavalent antimonial (SbV) that was historically the first-line treatment. However, significant resistance has developed, particularly in the Bihar region of India. * **Paromomycin (Option B):** An aminoglycoside antibiotic that acts as a potent leishmanicidal agent by inhibiting protein synthesis. It is often used in combination therapies. * **Miltefosine (Option C):** This is the **only oral drug** available for visceral leishmaniasis. It is highly effective but contraindicated in pregnancy due to its teratogenic potential. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice (DOC):** Liposomal **Amphotericin B** is currently the drug of choice for Visceral Leishmaniasis in India (single dose 10mg/kg). * **Post-Kala-azar Dermal Leishmaniasis (PKDL):** Miltefosine is commonly used for the extended treatment required in PKDL cases. * **Vector:** The disease is transmitted by the bite of the female sandfly (*Phlebotomus argentipes*). * **Diagnostic Gold Standard:** Demonstration of LD bodies (Amastigotes) in splenic or bone marrow aspirates. The rK39 rapid antigen test is used for field diagnosis.

Q: USG guided aspiration of a hepatic cyst shows anchovy sauce appearance of the aspirate. The patient is most probably infected with which of the following?

Entamoeba histolytica. **Explanation:** The correct answer is **Entamoeba histolytica**. **1. Why Entamoeba histolytica is correct:** The "anchovy sauce" appearance is a classic pathognomonic description of the aspirate from an **Amoebic Liver Abscess (ALA)**. This occurs when *E. histolytica* trophozoites travel from the colon to the liver via the portal circulation. The abscess does not contain true pus; instead, it consists of **liquefactive necrosis** of hepatocytes. The characteristic reddish-brown, thick, non-foul-smelling fluid resembles anchovy sauce due to the mixture of necrotic liver tissue and blood. **2. Why the other options are incorrect:** * **Balantidium coli:** While it causes dysentery similar to amoebiasis, it rarely spreads extra-intestinally and does not cause liver abscesses. * **Giardia lamblia:** This parasite inhabits the duodenum and upper jejunum. It causes malabsorption and steatorrhea but does not invade tissues or cause hepatic cysts. * **Toxoplasma gondii:** This is an intracellular parasite that typically presents with lymphadenopathy, encephalitis (in immunocompromised), or congenital infections. It does not produce large necrotic hepatic cysts. **3. High-Yield Clinical Pearls for NEET-PG:** * **Location:** ALA is most commonly found in the **Right Lobe** of the liver (due to the bulk of portal drainage). * **Microscopy:** The "anchovy sauce" aspirate usually contains **no trophozoites in the center**; they are found in the peripheral abscess wall. * **Diagnosis:** Indirect Hemagglutination (IHA) is the most sensitive serological test. * **Treatment:** Drug of choice is **Metronidazole**, followed by a luminal amoebicide (e.g., Paromomycin) to eradicate the intestinal colonization. * **Differential:** Do not confuse with **Hydatid cyst** (*Echinococcus granulosus*), which shows "clear spring water" fluid and "hydatid sand."

Question 1

Which of the following parasites can be detected in a peripheral blood smear?

Accepted Answer

Brucella

Answer

Malaria

Answer

Toxoplasma

Answer

Babesia

Question 2

What is a definitive host?

Accepted Answer

One in which sexual multiplication takes place

Answer

One in which asexual multiplication takes place

Answer

One that harbors the adult form

Answer

One that harbors the larval form

Question 3

What is the correct sequence of the malaria parasite life cycle stages?

Accepted Answer

Exoerythrocytic stage, Erythrocytic stage, Gametocytic stage, Sporogony

Answer

Exoerythrocytic stage, Gametocytic stage, Erythrocytic stage, Sporogony

Answer

Exoerythrocytic stage, Sporogony, Gametocytic stage, Erythrocytic stage

Answer

Exoerythrocytic stage, Sporogony, Erythrocytic stage, Gametocytic stage

Question 4

Which of the following are NOT seen in the peripheral smear in Plasmodium falciparum infection?

Accepted Answer

Maurer's dots and Schizonts

Answer

Schizonts and Acccolé

Answer

Maurer's dots and Acccolé

Answer

Acccolé and Shuffner's dots

Question 5

Auto infection occurs in which of the following organisms?

Accepted Answer

All of the above

Answer

Hymenolepis nana

Answer

Enterobius vermicularis

Answer

Taenia solium

Question 6

Which organism's filariform larva is infective?

Accepted Answer

Necator americanus

Answer

Enterobius vermicularis

Answer

Ascaris lumbricoides

Answer

Trichuris trichura

Question 7

The Sabin Feldman dye test is used for the diagnosis of which of the following conditions?

Accepted Answer

Toxoplasmosis

Answer

Trypanosomiasis

Answer

Kala-azar

Answer

Yellow fever

Question 8

Which drug is NOT used in the treatment of visceral leishmaniasis?

Accepted Answer

Hydroxychloroquine

Answer

Stibogluconate

Answer

Paromomycin

Answer

Miltefosine

Question 9

USG guided aspiration of a hepatic cyst shows anchovy sauce appearance of the aspirate. The patient is most probably infected with which of the following?

Accepted Answer

Entamoeba histolytica

Answer

Balantidium coli

Answer

Giardia lamblia

Answer

Toxoplasma gondii

Question 10

Which of the following helminths show their larval form in stool?

Accepted Answer

Ascaris lumbricoides

Answer

Strongyloides

Answer

Ancylostoma duodenale

Answer

Necator americanus

Parasitology — MCQs

Parasitology — MCQs

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