Parasitology Practice Questions

Q: Chronic dysentery, abdominal pain, and rectal prolapse in children is caused by which of the following parasites?

Trichuris trichura. **Explanation:** The correct answer is **Trichuris trichiura** (Whipworm). This parasite primarily inhabits the caecum and large intestine. In heavy infections, particularly in children, the worms can be found throughout the colon and rectum. **Why Trichuris trichiura is correct:** The hallmark clinical presentation of heavy Trichuriasis is **Trichuris Dysentery Syndrome**. The worms embed their slender anterior ends into the intestinal mucosa, causing chronic inflammation, mucosal friability, and blood loss. The constant irritation and straining (tenesmus) during defecation, combined with the weakening of the pelvic floor muscles and local inflammation, lead to the classic complication of **rectal prolapse**. **Analysis of Incorrect Options:** * **Enterobius vermicularis (Pinworm):** Primarily causes perianal pruritus (itching) at night. It does not cause dysentery or rectal prolapse. * **Ascaris lumbricoides (Roundworm):** Typically causes intestinal obstruction (bolus formation) or Loeffler’s syndrome (pulmonary phase). It does not typically cause chronic dysentery. * **Trichinella spiralis:** Known for causing muscle pain (myositis), periorbital edema, and eosinophilia after ingestion of undercooked pork. It does not inhabit the lower bowel to cause prolapse. **NEET-PG High-Yield Pearls:** * **Morphology:** Adult worm is whip-like (thick posterior, thin anterior). * **Egg:** Characteristic **barrel-shaped** (lemon-shaped) with **bipolar mucus plugs**. * **Treatment:** Mebendazole or Albendazole. * **Key Association:** Always link "Rectal Prolapse + Child + Dysentery" to *Trichuris trichiura*.

Q: What is the most virulent Plasmodium species causing malaria?

Falciparum. **Explanation:** **Plasmodium falciparum** is the most virulent species because of its unique ability to cause **sequestration** and **cytoadherence**. Unlike other species, *P. falciparum* expresses **PfEMP-1** (Plasmodium falciparum erythrocyte membrane protein 1) on the surface of infected RBCs. This protein binds to endothelial receptors (like ICAM-1 and CD36), causing infected cells to stick to capillary walls. This leads to microvascular obstruction, tissue hypoxia, and multi-organ failure, manifesting as **Cerebral Malaria**, Blackwater fever, or Acute Respiratory Distress Syndrome (ARDS). Furthermore, it can infect RBCs of all ages, leading to high levels of parasitemia (>5%). **Why other options are incorrect:** * **P. vivax & P. ovale:** These species preferentially infect **young RBCs (reticulocytes)**, limiting the total parasite load. While they cause significant morbidity and can relapse due to **hypnozoites** in the liver, they rarely cause the fatal microvascular complications seen in falciparum. * **P. malariae:** This species infects only **old RBCs**, resulting in the lowest parasitemia levels. It follows a 72-hour (quartan) cycle and is generally the most benign form, though it is associated with nephrotic syndrome in children. **High-Yield NEET-PG Pearls:** * **Maurer’s dots:** Seen in *P. falciparum* (Schüffner’s dots are seen in *P. vivax/ovale*). * **Multiple rings per RBC** and **banana-shaped gametocytes** are diagnostic hallmarks of *P. falciparum*. * **Recrudescence** is seen in *P. falciparum* (due to incomplete treatment), whereas **Relapse** is seen in *P. vivax/ovale* (due to hypnozoites).

Q: Peripheral smear of malaria shows which of the following findings, EXCEPT?

Banana shaped gametocyte - Ovale. The correct answer is **D. Banana shaped gametocyte - Ovale**. ### **Explanation** The diagnosis of malaria via peripheral smear relies on identifying specific morphological features of the *Plasmodium* species within red blood cells (RBCs). 1. **Why Option D is correct:** Banana-shaped (crescentic) gametocytes are the pathognomonic hallmark of ***Plasmodium falciparum***, not *P. ovale*. In *P. ovale* infections, the gametocytes are typically round or oval, and the infected RBCs often show fimbriated (ragged) edges and an oval shape. 2. **Why Option A is incorrect:** *P. vivax* typically presents with a **single ring form** (trophozoite) per RBC. The infected RBC is usually enlarged and contains Schüffner’s dots. 3. **Why Option B is incorrect:** **Multiple ring forms** (multiple parasites infecting a single RBC) and the "Accole/Applique" position (rings at the periphery of the RBC) are characteristic features of ***P. falciparum*** due to its high parasitemia levels. 4. **Why Option C is incorrect:** ***P. malariae*** is known for its unique **"Band and Bar" forms**, where the growing trophozoite stretches across the diameter of the non-enlarged RBC. ### **High-Yield Clinical Pearls for NEET-PG** * **Maurer’s Dots:** Seen in *P. falciparum*. * **Schüffner’s Dots:** Seen in *P. vivax* and *P. ovale*. * **Ziemann’s Dots:** Seen in *P. malariae*. * **RBC Age Preference:** *P. vivax/ovale* prefer young RBCs (reticulocytes); *P. malariae* prefers old RBCs; *P. falciparum* is "indiscriminate" (infects RBCs of all ages), leading to severe anemia and high parasite load. * **Gold Standard Diagnosis:** Microscopy (Thick smear for detection, Thin smear for species identification).

Q: What is the infective form of the malarial parasite transmitted through blood transfusion?

Trophozoite. ### Explanation The correct answer is **B. Trophozoite**. **1. Why Trophozoite is Correct:** In a natural infection via a female *Anopheles* mosquito, the infective form is the **sporozoite**. However, in **Transfusion-Induced Malaria**, the parasite is transmitted directly from the donor’s blood. Since the hepatic (pre-erythrocytic) cycle is bypassed, the blood contains asexual erythrocytic stages. Among these, the **trophozoite** (specifically the ring form) is the most common and persistent stage found in the donor's red blood cells that initiates infection in the recipient. **2. Analysis of Incorrect Options:** * **C. Sporozoite:** This is the infective form for **natural infection** via mosquito bite. Sporozoites are found in the mosquito's salivary glands and are absent in human blood during a transfusion. * **A. Merozoite & D. Schizont:** While these asexual stages are present in the blood, they are transient or represent a later stage of the erythrocytic cycle. The trophozoite is the primary diagnostic and infective stage circulating in the donor's blood. **3. NEET-PG High-Yield Pearls:** * **Incubation Period:** Transfusion malaria has a **shorter incubation period** because the pre-erythrocytic (liver) stage is bypassed. * **Relapse:** There is **no risk of relapse** (no hypnozoites) in transfusion malaria, even in *P. vivax* or *P. ovale*, because the liver stage never occurs. * **Drug of Choice:** Radical treatment with Primaquine is **not required** for transfusion malaria; only blood schizonticides (like Chloroquine) are needed. * **Storage:** Malarial parasites can survive in blood stored at 4°C for up to 2–3 weeks.

Q: Primary amoebic meningoencephalitis is caused by which organism?

Naegleria fowleri. **Explanation:** **Primary Amoebic Meningoencephalitis (PAM)** is a rapidly fatal central nervous system infection caused by **Naegleria fowleri**, often referred to as the "brain-eating amoeba." 1. **Why Naegleria fowleri is correct:** * **Pathogenesis:** It is a free-living thermophilic amoeba found in warm freshwater. It enters the body through the nasal mucosa while swimming or diving, penetrates the cribriform plate, and migrates along the olfactory nerves to the brain. * **Clinical Course:** It causes acute, fulminant hemorrhagic necrotizing meningoencephalitis in previously healthy individuals, leading to death within 7–10 days. 2. **Why other options are incorrect:** * **Entamoeba histolytica:** Causes intestinal amoebiasis and amoebic liver abscess. While it can rarely cause brain abscesses, it does not cause PAM. * **Escherichia coli:** A common cause of bacterial meningitis, particularly in neonates, but it is a bacterium, not an amoeba. * **Balamuthia mandrillaris:** Along with *Acanthamoeba*, this causes **Granulomatous Amoebic Encephalitis (GAE)**, which is a subacute or chronic infection typically seen in immunocompromised hosts, unlike the acute PAM caused by *Naegleria*. **High-Yield Clinical Pearls for NEET-PG:** * **Diagnostic Finding:** Wet mount of CSF shows **actively motile trophozoites** (slug-like movement). Note: Cysts are never seen in brain tissue or CSF in *Naegleria* infections. * **Drug of Choice:** Amphotericin B (often used in combination with Miltefosine). * **Key Differentiator:** PAM occurs in healthy individuals with a history of swimming; GAE occurs in immunocompromised individuals via skin lesions or inhalation.

Q: Which parasite penetrates the skin for entry into the body?

Ankylostoma duodenale. The correct answer is **Ankylostoma duodenale**. ### **Explanation** The primary mode of infection for certain helminths is the **percutaneous route**, where the infective larval stage (Filariform larva) actively penetrates the intact skin of a human host, usually through the feet when walking barefoot on contaminated soil. 1. **Ankylostoma duodenale (Hookworm):** The filariform larva penetrates the skin, enters the venous circulation, travels to the lungs, ascends the trachea, is swallowed, and finally matures in the small intestine. **Strongyloides stercoralis** also shares this mechanism; however, in the context of this specific question, *Ankylostoma* is the classic representative of skin-penetrating nematodes. 2. **Roundworm (Ascaris lumbricoides):** Infection occurs via the **fecal-oral route** through the ingestion of embryonated eggs in contaminated food or water. There is no skin penetration. 3. **Trichuris trichiura (Whipworm):** Infection occurs strictly via the **ingestion** of embryonated eggs. It does not have a tissue migratory phase or a skin-penetration phase. ### **NEET-PG High-Yield Pearls** * **The "Skin Penetrators" Mnemonic:** Remember **"S-A-N-D"** for parasites that enter through the skin: * **S:** *Strongyloides stercoralis* * **A:** *Ankylostoma duodenale* & *A. braziliense* (Cutaneous Larva Migrans) * **N:** *Necator americanus* * **D:** *Dermatobia hominis* (Botfly) / **Schistosomes** (Cercariae). * **Ground Itch:** This is the allergic reaction/pruritic dermatitis seen at the site of entry of Hookworm larvae. * **Loeffler’s Syndrome:** Characterized by transient pulmonary infiltrates and eosinophilia; it occurs during the lung migration phase of *Ankylostoma*, *Necator*, and *Ascaris*. Note: *Trichuris* does **not** cause Loeffler’s as it lacks a migratory cycle.

Q: Which statement is true regarding the trophozoites of E. histolytica?

Shows erythrophagocytosis. **Explanation:** *Entamoeba histolytica* is the causative agent of amoebiasis. Distinguishing it from the morphologically identical but non-pathogenic *E. dispar* is a common NEET-PG focus. **1. Why Option C is Correct:** The presence of **ingested Red Blood Cells (erythrophagocytosis)** within the cytoplasm of a trophozoite is the **pathognomonic** feature of *E. histolytica*. It indicates invasive disease, as the parasite actively destroys host tissue and consumes erythrocytes. This feature is never seen in *E. dispar* or *E. coli*. **2. Why Other Options are Incorrect:** * **Option A:** *E. histolytica* has a **central** karyosome (nucleolus). An **eccentric** (off-center) karyosome is a characteristic feature of *Entamoeba coli*, a non-pathogenic commensal. * **Option B:** The nuclear membrane of *E. histolytica* is lined with **fine, uniformly distributed peripheral chromatin**. A membrane "without chromatin" is not characteristic of this genus. * **Option D:** The presence of ingested bacteria is typical of **Entamoeba coli**. *E. histolytica* trophozoites in invasive disease usually contain RBCs but rarely contain bacteria, whereas commensal amoebae feed on intestinal flora. **High-Yield Clinical Pearls for NEET-PG:** * **Motility:** Trophozoites show unidirectional, purposeful movement using finger-like **pseudopodia**. * **Nuclear Structure:** Described as having a "Cartwheel appearance" due to the central karyosome and delicate chromatin. * **Stain of Choice:** Iron-hematoxylin or Trichrome stain. * **Quadrinucleate Cyst:** The infective stage; contains up to 4 nuclei, rounded chromatoid bars (cigar-shaped), and a glycogen mass.

Q: Lymphatic obstruction occurs with which of the following parasites?

Filarial worm. **Explanation:** **Correct Option: A. Filarial worm (*Wuchereria bancrofti* / *Brugia malayi*)** Lymphatic filariasis is primarily caused by *Wuchereria bancrofti*. The adult worms reside in the **afferent lymphatic vessels** and lymph nodes. The pathogenesis involves a combination of mechanical obstruction by the adult worms and a profound inflammatory response (Th2-mediated) to the parasite and its endosymbiont, *Wolbachia*. Over time, chronic inflammation leads to **lymphangiosclerosis** and fibrosis, resulting in permanent lymphatic obstruction, lymphoedema, and eventually **Elephantiasis**. **Incorrect Options:** * **B. Hookworm (*Ancylostoma duodenale*):** These reside in the small intestine and feed on blood. They are primarily associated with **Iron Deficiency Anemia** and ground itch, not lymphatic pathology. * **C. Guinea worm (*Dracunculus medinensis*):** The adult female migrates to the subcutaneous tissues (usually of the lower limbs) to create a blister and release larvae. It causes local ulcers and secondary infections but does not obstruct lymphatics. * **D. Pinworm (*Enterobius vermicularis*):** These inhabit the cecum and appendix. The hallmark clinical feature is **perianal pruritus** (nocturnal itching) as the female migrates to the perianal skin to lay eggs. **High-Yield Clinical Pearls for NEET-PG:** * **Vector:** *Culex quinquefasciatus* is the most common vector for *W. bancrofti* in India. * **Nocturnal Periodicity:** Microfilariae appear in the peripheral blood between **10 PM and 2 AM**. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough, wheezing, and high eosinophil counts. * **Drug of Choice:** Diethylcarbamazine (DEC). Note: DEC is contraindicated in Onchocerciasis due to the Mazzotti reaction. * **Diagnostic Gold Standard:** Demonstration of microfilariae in a peripheral blood smear (thick film).

Question 1

Chronic dysentery, abdominal pain, and rectal prolapse in children is caused by which of the following parasites?

Accepted Answer

Trichuris trichura

Answer

Enterobius vermicularis

Answer

Ascariasis

Answer

Trichinella spiralis

Question 2

Recurrent giardiasis is associated with which of the following conditions?

Accepted Answer

Common variable immunodeficiency

Answer

Severe combined immunodeficiency

Answer

DiGeorge syndrome

Answer

C8 deficiency

Question 3

What is the most virulent Plasmodium species causing malaria?

Accepted Answer

Falciparum

Answer

Vivax

Answer

Ovale

Answer

Malariae

Question 4

Peripheral smear of malaria shows which of the following findings, EXCEPT?

Accepted Answer

Banana shaped gametocyte - Ovale

Answer

Single ring form - Vivax

Answer

Multiple ring form - Falciparum

Answer

Bar and band forms - Malariae

Question 5

What is the infective form of the malarial parasite transmitted through blood transfusion?

Accepted Answer

Trophozoite

Answer

Merozoite

Answer

Sporozoite

Answer

Schizont

Question 6

Primary amoebic meningoencephalitis is caused by which organism?

Accepted Answer

Naegleria fowleri

Answer

Entamoeba histolytica

Answer

Escherichia coli

Answer

Balamuthia mandrillaris

Question 7

Which parasite penetrates the skin for entry into the body?

Accepted Answer

Ankylostoma duodenale

Answer

Strongyloides

Answer

Round worm

Answer

Trichuris trichura

Question 8

Which statement is true regarding the trophozoites of E. histolytica?

Accepted Answer

Shows erythrophagocytosis

Answer

Has an eccentric karyosome

Answer

Nuclear membrane is without chromatin

Answer

Presence of bacteria inside the cell

Question 9

All of the following statements about toxoplasmosis are true except?

Accepted Answer

Arthralgia, sore throat and abdominal pain are the most common manifestations

Answer

May spread by organ transplantation

Answer

Maternal infection acquired after 6 months has high risk of transmission

Answer

Oocyst in freshly passed cat's faeces is infective

Question 10

Lymphatic obstruction occurs with which of the following parasites?

Accepted Answer

Filarial worm

Answer

Hook worm

Answer

Guinea worm

Answer

Pin worm

Parasitology — MCQs

Parasitology — MCQs

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