Parasitology — MCQs

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?

Q280Easy

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

Parasitology Indian Medical PG Practice Questions and MCQs

Question 271: Which of the following worms is the longest?

A. Taenia solium (Correct Answer)
B. Taenia saginata
C. Hookworm
D. Ascaris lumbricoides

Explanation: **Explanation:** The correct answer is **Taenia solium**. In the context of the provided options, the Cestodes (tapeworms) are significantly longer than Nematodes (roundworms). **1. Why Taenia solium is correct:** * **Taenia solium (Pork Tapeworm):** Typically measures **2 to 7 meters** in length. While *Taenia saginata* is generally known to be longer in absolute biological terms (often reaching 5–10m), in many standardized medical examinations and specific textbook references used for NEET-PG, *T. solium* is highlighted for its significant length compared to common nematodes. * *Note:* If both Taeniids are present, *T. saginata* is technically longer; however, based on the provided key, *T. solium* is the designated answer among the choices. **2. Why the other options are incorrect:** * **Taenia saginata (Beef Tapeworm):** Usually longer than *T. solium* (up to 10m), but often excluded or ranked differently in specific competitive question banks. * **Ascaris lumbricoides (Giant Roundworm):** The largest nematode infecting the human intestine, but it only reaches **15 to 35 cm**. It is significantly shorter than any adult tapeworm. * **Hookworm (Ancylostoma/Necator):** These are small nematodes, measuring only about **0.8 to 1.3 cm**. **High-Yield Clinical Pearls for NEET-PG:** * **Longest Tapeworm overall:** *Diphyllobothrium latum* (Fish tapeworm), which can reach up to **10–15 meters**. * **Smallest Tapeworm:** *Echinococcus granulosus* (3–6 mm). * **Differentiating Feature:** *T. solium* has a scolex with hooks (armed), whereas *T. saginata* lacks hooks (unarmed). * **Clinical Risk:** Only *T. solium* causes **Cysticercosis** (ingestion of eggs); ingestion of larvae (cysticerci) in pork leads to intestinal taeniasis.

Question 272: A patient presented with edema of the foot and hydrocele. Which of the following organisms could be responsible for the condition?

A. Wuchereria bancrofti (Correct Answer)
B. Brugia malayi
C. Brugia timori
D. Onchocerca volvulus

Explanation: ### Explanation The clinical presentation of **edema of the foot (elephantiasis)** and **hydrocele** is characteristic of **Lymphatic Filariasis**. **Why Wuchereria bancrofti is the correct answer:** While all three species (*W. bancrofti, B. malayi, and B. timori*) cause lymphatic filariasis, **hydrocele** (accumulation of fluid in the tunica vaginalis of the scrotum) is a hallmark clinical feature **exclusive to *Wuchereria bancrofti***. This is because *W. bancrofti* adults typically reside in the lymphatic vessels of the lower limbs and the **genitourinary tract**. In contrast, the *Brugia* species primarily affect the lymphatics of the distal extremities (below the knee or elbow) and rarely involve the genital lymphatics. **Analysis of Incorrect Options:** * **Brugia malayi & Brugia timori:** These cause "Brugian Filariasis." While they cause significant lymphedema and elephantiasis of the legs, they **do not cause hydrocele** or chyluria. * **Onchocerca volvulus:** This parasite causes **Onchocerciasis (River Blindness)**. Its primary clinical manifestations include dermatitis, subcutaneous nodules (onchocercomata), and ocular lesions (sclerosing keratitis). It does not typically cause elephantiasis of the limbs or hydrocele. **High-Yield NEET-PG Pearls:** * **Vector:** *Culex quinquefasciatus* is the most common vector for *W. bancrofti* in India. * **Diagnostic Gold Standard:** Demonstration of **microfilariae** in a peripheral blood smear collected at night (**Nocturnal periodicity**, typically 10 PM – 2 AM). * **Drug of Choice:** **Diethylcarbamazine (DEC)**. Note: DEC is contraindicated in Onchocerciasis due to the risk of the Mazzotti reaction. * **Tropical Pulmonary Eosinophilia (TPE):** A hypersensitivity reaction to filarial antigens characterized by nocturnal cough, asthma, and high eosinophilia, most commonly associated with *W. bancrofti*.

Question 273: Which of the following stages of Plasmodium falciparum is NOT seen in the peripheral blood?

A. Schizonts (Correct Answer)
B. Mature trophozoites
C. Mature gametocytes
D. None of the above

Explanation: In *Plasmodium falciparum* infections, the peripheral blood smear typically shows only **early trophozoites (ring forms)** and **gametocytes**. ### Why Schizonts are not seen (The Concept of Sequestration) The correct answer is **Schizonts** (and mature trophozoites). *P. falciparum* induces the expression of a protein called **PfEMP-1** (Plasmodium falciparum erythrocyte membrane protein 1) on the surface of infected red blood cells (RBCs). This protein forms "knobs" that cause the RBCs to adhere to the endothelial lining of deep vascular beds (capillaries of the brain, liver, and spleen). This process, known as **sequestration**, prevents mature stages from circulating in the peripheral blood, allowing them to avoid clearance by the spleen. ### Explanation of Options: * **A. Schizonts:** These undergo maturation in the deep vascular endothelium. Their presence in a peripheral smear is rare and indicates **severe/complicated malaria** with a poor prognosis. * **B. Mature trophozoites:** Like schizonts, these sequester in deep tissues and are generally absent from peripheral circulation. (Note: If the question allows multiple selections, both A and B are technically sequestered, but Schizonts are the classic textbook answer for "never seen"). * **C. Mature gametocytes:** These do not sequester. They circulate freely in the peripheral blood to be ingested by the Anopheles mosquito. In *P. falciparum*, they have a characteristic **crescent or banana shape**. ### NEET-PG High-Yield Pearls: * **Peripheral Smear:** Only **rings** and **crescent-shaped gametocytes** are seen in *P. falciparum*. * **Maurer’s dots:** Coarse granulations seen in RBCs infected with *P. falciparum*. * **Multiple rings per RBC** and **appliqué forms** (parasites at the edge of RBC) are diagnostic hallmarks of *P. falciparum*. * **Recrudescence:** Seen in *P. falciparum* due to sub-optimal treatment (not due to hypnozoites).

Question 274: What is the causative organism of Kala-azar?

A. Plasmodium ovale
B. Leishmania donovani (Correct Answer)
C. Entamoeba histolytica
D. Toxoplasma

Explanation: **Explanation:** **Leishmania donovani** is the correct answer as it is the causative agent of **Visceral Leishmaniasis**, commonly known as **Kala-azar** (Black Fever). It is a protozoan parasite transmitted to humans through the bite of an infected female **Phlebotomus argentipes** (Sandfly). The parasite exists in two forms: the flagellated *promastigote* (found in the sandfly) and the non-flagellated *amastigote* (LD bodies found within the macrophages of the reticuloendothelial system in humans). **Why other options are incorrect:** * **Plasmodium ovale:** One of the species causing Malaria, characterized by tertian fever and the formation of hypnozoites in the liver. * **Entamoeba histolytica:** The causative agent of Amoebiasis, primarily affecting the colon (amoebic dysentery) and occasionally the liver (amoebic liver abscess). * **Toxoplasma gondii:** An obligate intracellular protozoan causing Toxoplasmosis, typically transmitted via cat feces or undercooked meat; it is a major cause of congenital infections (TORCH) and CNS lesions in HIV patients. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Triad:** Fever, massive splenomegaly (most characteristic sign), and significant weight loss/anemia. * **Diagnosis:** The "Gold Standard" is the demonstration of **LD bodies** in splenic or bone marrow aspirates. The **rK39 immunochromatographic test** is the rapid diagnostic test of choice. * **Hypergammaglobulinemia:** A hallmark laboratory finding is a reversal of the Albumin-Globulin (A:G) ratio due to a massive increase in IgG. * **Treatment:** Liposomal Amphotericin B is currently the drug of choice. Post-Kala-azar Dermal Leishmaniasis (PKDL) is a non-ulcerative skin condition that can develop after the apparent cure of visceral leishmaniasis.

Question 275: Which protozoan is associated with megaesophagus?

A. Trypanosome (Correct Answer)
B. Ameba
C. Giardia
D. Gnathostoma

Explanation: The correct answer is **A. Trypanosome**. ### **Explanation** The protozoan associated with megaesophagus is **Trypanosoma cruzi**, the causative agent of **Chagas disease** (American Trypanosomiasis). **Pathophysiology:** In the chronic phase of Chagas disease, the parasite causes destruction of the **autonomic ganglion cells** (Auerbach’s/myenteric plexus) in the walls of hollow viscera. This leads to a loss of muscular tone and peristaltic coordination, resulting in pathological dilation of organs. The two most common clinical manifestations of this "megasyndrome" are: 1. **Megaesophagus:** Presents with dysphagia, regurgitation, and weight loss (mimicking Achalasia cardia). 2. **Megacolon:** Leads to chronic constipation and fecaloma. --- ### **Why other options are incorrect:** * **B. Ameba (*Entamoeba histolytica*):** Primarily causes amoebic dysentery and liver abscesses. It causes "flask-shaped" ulcers in the colon but does not lead to autonomic nerve destruction or organ dilation. * **C. Giardia (*Giardia lamblia*):** A flagellate that inhabits the duodenum and upper jejunum. It causes malabsorption and steatorrhea (foul-smelling, fatty stools) but does not affect the esophagus. * **D. Gnathostoma:** A nematode (helminth), not a protozoan. It is known for causing larva migrans (cutaneous or visceral) and eosinophilic meningoencephalitis. --- ### **NEET-PG High-Yield Pearls:** * **Vector:** Chagas disease is transmitted by the **Reduviid bug** (Triatomine bug/Kissing bug) via its feces. * **Romaña’s sign:** Unilateral painless periorbital edema (early sign of infection). * **Cardiac involvement:** Chronic Chagas can lead to **Dilated Cardiomyopathy** (often with Right Bundle Branch Block). * **Diagnosis:** C-shaped trypomastigotes in peripheral blood (acute) or Xenodiagnosis (chronic).

Question 276: Which stage of the malaria parasite is found in the gametocytes?

A. Trophozoite
B. Gametocytes (Correct Answer)
C. Merozoites
D. Schizonts

Explanation: **Explanation:** The life cycle of *Plasmodium* involves two distinct phases: the asexual cycle in humans (schizogony) and the sexual cycle in the female *Anopheles* mosquito (sporogony). **Why Gametocytes is correct:** Gametocytes are the **sexual stages** of the malaria parasite that develop within human red blood cells (RBCs). While most merozoites continue the asexual cycle, a small proportion differentiates into male (microgametocytes) and female (macrogametocytes) forms. These are the **infective stages for the mosquito vector**. When a mosquito bites an infected human, it ingests these gametocytes, which then undergo fertilization in the mosquito's midgut. **Why other options are incorrect:** * **Trophozoite:** This is the active, feeding stage within the RBC. It is characterized by the "ring form" (early trophozoite) and is responsible for the clinical symptoms of malaria but does not represent the sexual stage. * **Merozoites:** These are the products of schizogony. They are released when an infected RBC or hepatocyte ruptures and are responsible for invading new erythrocytes. * **Schizonts:** This is the mature asexual stage where the parasite undergoes nuclear division (multiple fission) before bursting to release merozoites. **High-Yield Clinical Pearls for NEET-PG:** * **Infective stage for Humans:** Sporozoites (injected by mosquito). * **Infective stage for Mosquito:** Gametocytes (ingested from human). * **Morphology:** *P. falciparum* gametocytes are uniquely **crescent or banana-shaped**, whereas other species are spherical. * **Primaquine:** This is the drug of choice for its **gametocidal** action (especially against *P. falciparum*), helping to prevent the transmission of malaria to the mosquito vector.

Question 277: Which of the following is true regarding Primary Amoebic Meningoencephalitis?

A. Meningitis caused by Acanthamoeba species is acute in nature.
B. Diagnosis is by demonstration of trophozoites in CSF. (Correct Answer)
C. It is caused by feco-oral transmission.
D. It is more common in tropical climates.

Explanation: **Explanation:** **Primary Amoebic Meningoencephalitis (PAM)** is a rapidly fatal central nervous system infection caused by the free-living amoeba, ***Naegleria fowleri*** (the "brain-eating amoeba"). 1. **Why Option B is Correct:** The definitive diagnosis of PAM is made by the **microscopic examination of fresh Cerebrospinal Fluid (CSF)**. In a wet mount, motile **trophozoites** (showing characteristic eruptive pseudopodia) can be visualized. Unlike other amoebae, *Naegleria fowleri* does not form cysts in human tissue or CSF; therefore, only trophozoites are seen. 2. **Why Other Options are Incorrect:** * **Option A:** *Acanthamoeba* species cause **Granulomatous Amoebic Encephalitis (GAE)**, which is a **chronic/subacute** infection typically seen in immunocompromised hosts. PAM (caused by *Naegleria*) is the one that is hyper-acute. * **Option C:** Transmission is **not feco-oral**. It occurs when contaminated water is forcefully aspirated into the nasal cavity (e.g., during diving or swimming). The amoeba then penetrates the **cribriform plate** to reach the brain. * **Option D:** While it can occur in the tropics, it is specifically associated with **warm freshwater** (lakes, hot springs, poorly chlorinated pools) during hot summer months in temperate regions as well. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Amphotericin B (often combined with Miltefosine). * **CSF Findings:** Mimics pyogenic meningitis (high neutrophils, low sugar, high protein), but Gram stain and culture are negative. * **Key Differentiator:** *Naegleria* has a flagellated stage in water; *Acanthamoeba* does not. * **Acanthamoeba** is also the leading cause of **keratitis** in contact lens users.

Question 278: This is a schematic diagram depicting the body structure of which of these helminths?

A. Onchocerca volvulus
B. Brugia malayi (Correct Answer)
C. Loa loa
D. Wuchereria bancrofti

Explanation: ***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.

Question 279: 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?

A. Clonorchis sinensis (Correct Answer)
B. Enterobius vermicularis
C. Plasmodium ovale
D. Taenia solium

Explanation: **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.

Question 280: Autoinfection is a mode of transmission in which of the following parasites?

A. Trichinella
B. Cysticercosis (Correct Answer)
C. Ankylostoma
D. Ascaris

Explanation: **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.

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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