Parasitology Practice Questions

Q: This is a schematic diagram depicting the body structure of which of these helminths?

Brugia malayi. ***Brugia malayi*** - Microfilariae have a **sheath** and **two discrete nuclei at the tail tip**, which are key distinguishing features visible in microscopic examination. - Causes **lymphatic filariasis** in Southeast Asia and is transmitted by **Mansonia** and **Anopheles** mosquitoes. *Onchocerca volvulus* - Microfilariae are **unsheathed** and have **no nuclei in the tail**, making them easily distinguishable from sheathed filariae. - Causes **river blindness (onchocerciasis)** and is transmitted by **Simulium** blackflies, primarily in Africa. *Loa loa* - Microfilariae have a **sheath** but show **nuclei extending to the tail tip** in a continuous pattern, unlike the discrete tail nuclei of Brugia. - Causes **loiasis** with characteristic **calabar swellings** and **eye worm** migration, endemic to Central and West Africa. *Wuchereria bancrofti* - Microfilariae have a **sheath** but **no nuclei in the tail tip**, distinguishing it from Brugia malayi's discrete tail nuclei. - Most common cause of **lymphatic filariasis** globally, transmitted by **Culex**, **Aedes**, and **Anopheles** mosquitoes.

Q: An immigrant from the Far East develops malaise, fever, and rigors, followed by upper right quadrant abdominal pain, vomiting, jaundice, and itching. His urine is dark and his feces are pale. Infestation with which of the following parasites is most strongly suggested by this patient's presentation?

Clonorchis sinensis. **Explanation:** The patient presents with **obstructive jaundice** (dark urine, pale stools, itching, and jaundice) and symptoms of **acute cholangitis** (fever, rigors, and RUQ pain). Given the patient's origin from the **Far East**, the most likely diagnosis is infestation with **Clonorchis sinensis** (Chinese Liver Fluke). 1. **Why Clonorchis sinensis is correct:** This parasite is endemic to East Asia. Humans are infected by consuming undercooked freshwater fish containing metacercariae. The larvae migrate to the **biliary tree**, where adult flukes cause mechanical obstruction, inflammation, and hyperplasia of the biliary epithelium. This leads to biliary stasis, secondary bacterial cholangitis, and pigment stone formation. 2. **Why other options are incorrect:** * **Enterobius vermicularis:** Causes perianal pruritus (pinworm), not biliary obstruction or jaundice. * **Plasmodium ovale:** Causes malaria with cyclical fever and hemolysis. While it can cause jaundice (pre-hepatic), it does not cause RUQ pain typical of biliary obstruction or pale stools. * **Taenia solium:** Causes intestinal taeniasis or cysticercosis (neurocysticercosis). It does not typically involve the biliary tract. **High-Yield Clinical Pearls for NEET-PG:** * **Classic Association:** Chronic *Clonorchis sinensis* infection is a major risk factor for **Cholangiocarcinoma** (bile duct cancer). * **Diagnosis:** Identification of characteristic **operculated eggs** with "shoulders" and a small knob at the posterior pole in stool or bile. * **Treatment:** **Praziquantel** is the drug of choice. * **Intermediate Hosts:** 1st—Snail; 2nd—Freshwater (Cyprinid) fish.

Q: Autoinfection is a mode of transmission in which of the following parasites?

Cysticercosis. **Explanation:** **Autoinfection** occurs when an individual serves as both the reservoir and the host, leading to a cycle of infection without an external environmental stage. **Why Cysticercosis is Correct:** Cysticercosis is caused by the larval stage of *Taenia solium* (Pork tapeworm). While humans are the definitive hosts for the adult worm, they can become intermediate hosts for the larvae through **internal or external autoinfection**. * **External:** Fecal-oral contamination (ingesting eggs from one’s own stool). * **Internal:** Reverse peristalsis carries gravid proglottids from the intestine back to the stomach, where eggs hatch, penetrate the mucosa, and disseminate to tissues (brain, muscles). **Analysis of Incorrect Options:** * **A. Trichinella spiralis:** Transmission occurs via the ingestion of undercooked meat containing encysted larvae. There is no autoinfection cycle; the larvae must be ingested from an external source. * **C. Ancylostoma duodenale:** Transmission occurs via the penetration of the skin by filariform larvae found in the soil. * **D. Ascaris lumbricoides:** Infection occurs by ingesting embryonated eggs from contaminated soil. Eggs require a period of maturation (3 weeks) outside the host to become infective, making autoinfection impossible. **NEET-PG High-Yield Pearls:** * **Other parasites showing autoinfection:** *Strongyloides stercoralis* (most common cause of hyperinfection), *Enterobius vermicularis* (Pinworm), *Hymenolepis nana* (Dwarf tapeworm), and *Cryptosporidium hominis*. * **Neurocysticercosis (NCC):** The most common cause of adult-onset seizures in India; "Starry sky" appearance on CT/MRI is a classic finding. * **Strongyloides:** Unique because the rhabditiform larvae can transform into infective filariform larvae *within* the host's gut.

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).

Question 1

This is a schematic diagram depicting the body structure of which of these helminths?

Accepted Answer

Brugia malayi

Answer

Onchocerca volvulus

Answer

Loa loa

Answer

Wuchereria bancrofti

Question 2

An immigrant from the Far East develops malaise, fever, and rigors, followed by upper right quadrant abdominal pain, vomiting, jaundice, and itching. His urine is dark and his feces are pale. Infestation with which of the following parasites is most strongly suggested by this patient's presentation?

Accepted Answer

Clonorchis sinensis

Answer

Enterobius vermicularis

Answer

Plasmodium ovale

Answer

Taenia solium

Question 3

Autoinfection is a mode of transmission in which of the following parasites?

Accepted Answer

Cysticercosis

Answer

Trichinella

Answer

Ankylostoma

Answer

Ascaris

Question 4

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 5

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 6

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 7

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 8

Pulmonary eosinophilia is seen in the following parasitic infections except?

Accepted Answer

Babesiosis

Answer

Hookworm infection

Answer

Strongyloidiasis

Answer

Visceral larva migrans

Question 9

What is the cause of larva currens?

Accepted Answer

Strongyloides stercoralis

Answer

Necator americanus

Answer

Ankylostoma duodenale

Answer

Hymenolepis nana

Question 10

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

Accepted Answer

IgE

Answer

IgA

Answer

IgG

Answer

IgM

Parasitology — MCQs

Parasitology — MCQs

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