Parasitology Practice Questions

Q: Which of the following statements best describes intestinal amebae?

They can cause peritonitis and liver abscesses.. ### Explanation **Correct Option: C. They can cause peritonitis and liver abscesses.** *Entamoeba histolytica* is the primary pathogen among intestinal amebae. It possesses proteolytic enzymes (histolysin) that allow it to invade the colonic mucosa, causing "flask-shaped" ulcers. If the ulcer perforates the bowel wall, it leads to **peritonitis**. Furthermore, trophozoites can enter the portal circulation and travel to the liver, where they cause **Amoebic Liver Abscess (ALA)**, characterized by "anchovy sauce" pus. **Why other options are incorrect:** * **Option A:** While many species (like *E. coli* or *E. dispar*) are nonpathogenic, the group includes *E. histolytica*, a major cause of global morbidity. In a clinical/exam context, "intestinal amebae" typically focuses on the significant pathology of *E. histolytica*. * **Option B:** Transmission occurs via the **fecal-oral route** through the ingestion of mature **quadrinucleate cysts**. Trophozoites are labile and are destroyed by gastric acid; they are not the infectious stage. * **Option D:** *E. histolytica* primarily inhabits the **large intestine** (cecum and colon), not the duodenum. (Note: *Giardia* is the parasite typically associated with the duodenum/jejunum). **NEET-PG High-Yield Pearls:** * **Infective Stage:** Mature quadrinucleate cyst. * **Diagnostic Stage:** Trophozoite (containing ingested RBCs/erythrophagocytosis) or cyst in stool. * **Pathognomonic Sign:** Erythrophagocytosis by trophozoites is the definitive feature of *E. histolytica* (distinguishing it from the morphologically identical *E. dispar*). * **Drug of Choice:** Metronidazole or Tinidazole (followed by a luminal amebicide like Paromomycin to eradicate cysts).

Q: Man is the intermediate host for which of the following parasitic infections?

Hydatid cyst. **Explanation** In parasitology, the **Definitive Host** is where the parasite reaches maturity and undergoes sexual reproduction, while the **Intermediate Host** harbors the larval or asexual stages. **Why Hydatid Cyst is correct:** Hydatid disease is caused by the tapeworm *Echinococcus granulosus*. * **Definitive Host:** Dogs (and other canines), which harbor the adult worm in their intestines. * **Intermediate Host:** Normally sheep or cattle. **Humans act as accidental intermediate hosts** by ingesting eggs (via contaminated food/water or contact with dogs). In humans, the eggs hatch into oncospheres that migrate to organs (liver, lungs) to form **larval cysts** (Hydatid cysts). Because the cycle usually ends with the human, we are also considered "dead-end hosts." **Why other options are incorrect:** * **Kala-azar (Visceral Leishmaniasis):** Humans are the **definitive host** (harboring the amastigote stage), while the Sandfly (*Phlebotomus*) is the intermediate host/vector. * **Filariasis (*W. bancrofti*):** Humans are the **definitive host** (harboring adult worms in lymphatics), while the Mosquito (*Culex*) is the intermediate host/vector. **High-Yield Clinical Pearls for NEET-PG:** 1. **Man as Intermediate Host:** Remember the mnemonic **"THE"** — **T**aenia solium (Cysticercosis), **H**ydatid disease, **E**chinococcus, and Malaria (*Plasmodium*). 2. **Malaria Exception:** In Malaria, humans are the **intermediate host** (asexual cycle), and the Female Anopheles mosquito is the **definitive host** (sexual cycle). 3. **Hydatid Cyst Diagnosis:** Look for "Eggshell calcification" on X-ray or "Water lily sign" on USG/CT. Casoni’s test is a historical skin test for this.

Q: Which of the following is FALSE about Leishmaniasis?

Aldehyde Test of Napier is a good test for diagnosis.. **Explanation:** The correct answer is **A** because the **Aldehyde Test of Napier** is **not** a "good" (specific) test for the diagnosis of Visceral Leishmaniasis (Kala-azar). It is a non-specific biochemical test that relies on hypergammaglobulinemia. It only becomes positive after 3 months of infection and can be falsely positive in other conditions like Multiple Myeloma, Schistosomiasis, and Cirrhosis. Modern diagnosis relies on the **rK39 immunochromatographic test** (highly sensitive/specific) or bone marrow/splenic aspiration. **Analysis of other options:** * **Option B:** Indian Leishmaniasis (*L. donovani*) is unique because it is **anthroponotic** (man is the sole reservoir). In contrast, Leishmaniasis in other parts of the world (e.g., Mediterranean or South America) is often zoonotic, involving canines or rodents. * **Option C:** **Leishmania-HIV co-infection** is a significant emerging public health challenge. HIV increases the risk of developing clinical Leishmaniasis by 100 to 2320 times, and Leishmaniasis accelerates the progression of HIV. * **Option D:** Currently, there are **no vaccines or chemoprophylactic drugs** available for personal prophylaxis against Leishmaniasis. Prevention relies entirely on vector control (sandfly) and personal protective measures (nets/repellents). **High-Yield NEET-PG Pearls:** * **Vector:** Female Sandfly (*Phlebotomus argentipes*). * **Infective stage:** Promastigote; **Diagnostic stage:** Amastigote (LD bodies). * **Drug of Choice:** Liposomal Amphotericin B (Single dose is now the standard in India). * **Post-Kala-azar Dermal Leishmaniasis (PKDL):** Occurs in 10% of cases in India after apparent cure; serves as an important reservoir for transmission.

Q: Which of the following is true about Plasmodium falciparum?

Accole forms are seen. **Explanation:** *Plasmodium falciparum* is the most virulent species of malaria, characterized by high levels of parasitemia and specific morphological features in peripheral blood smears. **1. Why "Accole forms" is correct:** In *P. falciparum* infections, young trophozoites (rings) are often seen at the very periphery of the Red Blood Cell (RBC), appearing as if they are "stuck" to the external margin of the cell membrane. These are known as **Accole or Applique forms**. This occurs because *P. falciparum* can infect RBCs of all ages, leading to high density and multiple rings per cell. **2. Why other options are incorrect:** * **James dots:** These are characteristic of *Plasmodium ovale*. In contrast, *P. falciparum* exhibits **Maurer’s dots**, while *P. vivax* shows **Schüffner’s dots**. * **Relapses:** Relapses occur due to the activation of dormant liver stages called **hypnozoites**. These are only found in *P. vivax* and *P. ovale*. *P. falciparum* does not have a hypnozoite stage; therefore, it causes **recrudescence** (due to surviving blood stages), not relapse. * **Longest incubation period:** *P. falciparum* has the **shortest** incubation period (approx. 12 days). The longest incubation period is seen in *P. malariae* (up to 30 days or more). **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Look for **crescent/banana-shaped gametocytes** and multiple rings per RBC. * **Sequestration:** *P. falciparum* causes RBCs to develop "knobs," leading to cytoadherence and sequestration in deep capillaries, which results in **Cerebral Malaria**. * **RBC Age:** It infects RBCs of **all ages**, unlike *P. vivax* (reticulocytes) or *P. malariae* (old RBCs).

Q: What is the cause of larva currens?

Strongyloides stercoralis. **Explanation:** **1. Why Strongyloides stercoralis is Correct:** Larva currens (meaning "racing larva") is a pathognomonic cutaneous manifestation of **Strongyloides stercoralis** infection. It is a form of cutaneous larva migrans caused by the rapid migration of filariform larvae in the dermis. Unlike other larval migrations, larva currens is characterized by its **extreme speed** (moving up to 5–10 cm per hour). It typically presents as an intensely pruritic, erythematous, linear or serpiginous wheal, most commonly found around the perianal region, buttocks, or thighs due to the parasite's unique **autoinfection** cycle. **2. Why the Other Options are Incorrect:** * **Necator americanus & Ancylostoma duodenale (Hookworms):** These cause **Cutaneous Larva Migrans (Ground Itch)**. However, the classic "creeping eruption" is more commonly associated with animal hookworms (*A. braziliense*). Compared to larva currens, these migrations are much slower (only a few millimeters to centimeters per day). * **Hymenolepis nana (Dwarf Tapeworm):** This is a cestode that resides in the intestine. While it also features an internal autoinfection cycle, it does not have a larval skin-migration phase and therefore does not cause larva currens. **3. High-Yield NEET-PG Pearls:** * **Autoinfection:** *S. stercoralis* is unique because rhabditiform larvae can transform into infective filariform larvae within the host's intestine, leading to chronic infection lasting decades. * **Hyperinfection Syndrome:** In immunocompromised patients (especially those on **corticosteroids**), the autoinfection cycle accelerates, leading to massive larval dissemination to organs like the lungs and CNS. * **Diagnosis:** The gold standard is the **Baermann culture technique** or agar plate culture to detect larvae in stool. * **Drug of Choice:** **Ivermectin** is the preferred treatment (superior to Albendazole).

Q: Which one of the following immunoglobulins is characteristically elevated in filariasis?

IgE. **Explanation:** In helminthic infections like **Filariasis** (caused by *Wuchereria bancrofti* or *Brugia malayi*), the immune system primarily mounts a **Type 2 helper T cell (Th2) response**. This response is characterized by the secretion of cytokines such as IL-4 and IL-5. IL-4 induces B-cell class switching to produce **IgE**, while IL-5 leads to the recruitment and activation of **eosinophils**. Elevated serum IgE levels and peripheral blood eosinophilia are hallmark laboratory findings in lymphatic filariasis and Tropical Pulmonary Eosinophilia (TPE). **Analysis of Options:** * **IgE (Correct):** It is the primary immunoglobulin involved in the defense against multicellular parasites. It binds to mast cells and basophils, triggering the release of inflammatory mediators that help combat the larvae. * **IgA:** Primarily involved in mucosal immunity (secretory IgA). While it may be present in the gut during intestinal helminthiasis, it is not the characteristic marker for systemic filarial infection. * **IgG:** While filarial-specific IgG (especially IgG4) increases during chronic infection, it is not as characteristically diagnostic or pathognomonic as the elevation of IgE in the context of the Th2 allergic-type response. * **IgM:** This is the first antibody produced in an acute infection (primary response) but is not specifically associated with the chronic, eosinophilic nature of parasitic infestations. **High-Yield Pearls for NEET-PG:** * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to microfilariae in the lungs, characterized by massive elevation of IgE (>1000 IU/mL) and extreme eosinophilia. * **Drug of Choice:** Diethylcarbamazine (DEC) is the standard treatment for filariasis. * **Diagnostic Gold Standard:** Demonstration of microfilariae in a **peripheral blood smear** (collected at night, between 10 PM and 2 AM, due to nocturnal periodicity).

Q: A patient presents with complaints of lower abdominal pain, fever, and repeated stools containing little fecal matter, blood, and mucus. Microscopy of the stool shows a paucity of WBCs and a positive test for heme. Which is the likely causative organism?

Entamoeba. ### Explanation The clinical presentation of lower abdominal pain, fever, and frequent small-volume stools containing blood and mucus is classic for **Amoebic Dysentery**, caused by *Entamoeba histolytica*. **Why Entamoeba is correct:** The defining feature in this question is the **"paucity of WBCs"** (pus cells) in the stool. *E. histolytica* produces a cytotoxin that lyses leukocytes (leukocytolysis). Therefore, despite being an invasive infection, the stool microscopy shows few inflammatory cells, RBCs in clumps (due to erythrophagocytosis), and a positive heme test. This contrasts with Bacillary Dysentery (e.g., *Shigella*), which presents with numerous pus cells. **Why other options are incorrect:** * **Giardia:** Causes malabsorptive "steatorrhea" (foul-smelling, fatty stools). It is non-invasive, so it does **not** cause blood or mucus in the stool. * **Staphylococcus & Clostridium perfringens:** These typically cause **food poisoning** characterized by watery diarrhea and vomiting due to preformed toxins or enterotoxins. They do not typically cause a dysenteric picture with blood and mucus. **NEET-PG High-Yield Pearls:** * **Stool Microscopy:** Look for **Trophozoites with ingested RBCs** (pathognomonic for *E. histolytica*). * **Flask-shaped ulcers:** The characteristic lesion formed in the colon. * **Charcot-Leyden crystals:** Often found in the stool due to eosinophil breakdown. * **Treatment:** Metronidazole or Tinidazole (Tissue amoebicides) followed by Diloxanide furoate (Luminal amoebicide) to clear the carrier state.

Q: The prepatent period in lymphatic filariasis is defined as the time interval between inoculation of infective larvae and which of the following?

First appearance of detectable microfilaria. ### Explanation **Concept Overview:** In parasitology, the **prepatent period** is the time interval between the entry of the infective stage of a parasite into the host and the earliest time at which its presence can be demonstrated (usually via the detection of eggs, larvae, or microfilariae in clinical samples). **Why Option B is Correct:** In Lymphatic Filariasis, the infective stage is the **L3 larvae** (inoculated by the mosquito). These larvae migrate to the lymphatics and mature into adult worms. The prepatent period ends when these adult worms mate and produce **microfilariae (mf)** that can be detected in the peripheral blood. For *Wuchereria bancrofti*, this period typically lasts **8 to 12 months**. **Analysis of Incorrect Options:** * **Option A & C (Blockage/Lymphoedema):** These represent the **Incubation Period** (time between infection and clinical symptoms) or the chronic stage of the disease. The prepatent period is a biological timeline, whereas these are clinical milestones. * **Option D (Development of adult worm):** While the development of the adult worm occurs during the prepatent period, the period only "ends" once the worm begins producing detectable offspring (microfilariae). **High-Yield NEET-PG Pearls:** * **Infective Stage:** L3 Larvae (transmitted by *Culex quinquefasciatus* for Bancroftian filariasis). * **Diagnostic Stage:** Microfilaria (detected via peripheral blood smear, ideally collected between 10 PM – 2 AM due to nocturnal periodicity). * **Incubation Period:** Usually 8–16 months (longer than the prepatent period). * **Drug of Choice:** Diethylcarbamazine (DEC) 6mg/kg for 12 days. * **National Target:** The Global Programme to Eliminate Lymphatic Filariasis (GPELF) aims for **elimination**, not eradication, primarily through Mass Drug Administration (MDA).

Question 1

Which of the following statements best describes intestinal amebae?

Accepted Answer

They can cause peritonitis and liver abscesses.

Answer

They are usually nonpathogenic.

Answer

They are usually transmitted as trophozoites.

Answer

They occur most abundantly in the duodenum.

Question 2

Man is the intermediate host for which of the following parasitic infections?

Accepted Answer

Hydatid cyst

Answer

Kala azar

Answer

Filariasis

Answer

All of the above

Question 3

Which of the following is FALSE about Leishmaniasis?

Accepted Answer

Aldehyde Test of Napier is a good test for diagnosis.

Answer

Indian Leishmaniasis is a non-zoonotic infection with man as the sole reservoir.

Answer

Co-infection with AIDS is now emerging.

Answer

There are no drugs for personal prophylaxis.

Question 4

Which of the following is true about Plasmodium falciparum?

Accepted Answer

Accole forms are seen

Answer

James dots are seen

Answer

Relapses are frequent

Answer

Longest incubation period

Question 5

Pulmonary eosinophilia is seen in the following parasitic infections except?

Accepted Answer

Babesiosis

Answer

Hookworm infection

Answer

Strongyloidiasis

Answer

Visceral larva migrans

Question 6

What is the cause of larva currens?

Accepted Answer

Strongyloides stercoralis

Answer

Necator americanus

Answer

Ankylostoma duodenale

Answer

Hymenolepis nana

Question 7

Which one of the following immunoglobulins is characteristically elevated in filariasis?

Accepted Answer

IgE

Answer

IgA

Answer

IgG

Answer

IgM

Question 8

A patient presents with complaints of lower abdominal pain, fever, and repeated stools containing little fecal matter, blood, and mucus. Microscopy of the stool shows a paucity of WBCs and a positive test for heme. Which is the likely causative organism?

Accepted Answer

Entamoeba

Answer

Giardia

Answer

Staphylococcus

Answer

Clostridium perfringens

Question 9

The prepatent period in lymphatic filariasis is defined as the time interval between inoculation of infective larvae and which of the following?

Accepted Answer

First appearance of detectable microfilaria

Answer

Blockage of lymphatics

Answer

Development of lymphoedema

Answer

Development of adult worm

Question 10

Which of the following statements is true regarding Acanthamoeba keratitis?

Accepted Answer

Acanthamoeba does not depend upon a human host for the completion of its life-cycle.

Answer

For the isolation of the causative agent, corneal scraping should be cultured on a nutrient agar plate.

Answer

The causative agent, Acanthamoeba is a helminth whose normal habitat is soil.

Answer

Keratitis due to Acanthamoeba is not seen in the immunocompromised patient.

Parasitology — MCQs

Parasitology — MCQs

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