Parasitology Practice Questions

Q: A 52-year-old male with HIV presents with profuse, watery diarrhea of 5 days’ duration. A biopsy of the small intestine is shown here. What is the most likely cause of this patient’s symptoms?

Cryptosporidium spp.. ***Cryptosporidium spp.*** - The image shows numerous **small, round, purple-stained organisms** adhering to the brush border of intestinal epithelial cells, which are characteristic of *Cryptosporidium* oocysts. - In an **HIV-positive patient** with profuse, watery diarrhea, *Cryptosporidium* is a common opportunistic infection that can cause severe and prolonged symptoms, especially when CD4 count is <200 cells/μL. - Diagnosis is confirmed by identifying **acid-fast oocysts** (3-6 μm) attached to the intestinal epithelial surface. *Giardia lamblia* - *Giardia* typically presents as pear-shaped **trophozoites** with flagella or oval **cysts** in the intestinal lumen, which are much larger (10-20 μm) than the organisms seen in this biopsy. - While *Giardia* can cause diarrhea in immunocompromised individuals, the morphology and location (attached to brush border vs. free in lumen) do not match. *Cystoisospora belli* - *Cystoisospora* (formerly *Isospora belli*) is another important cause of chronic diarrhea in HIV patients but appears as **large, elongated oocysts** (20-30 μm) that are acid-fast positive. - The organisms are typically found **within enterocytes** or in the lumen, not as small spherical structures on the brush border surface as seen here. *Cyclospora cayetanensis* - *Cyclospora* causes watery diarrhea in immunocompromised patients and appears as **round oocysts** (8-10 μm), larger than *Cryptosporidium*. - The oocysts are typically found in the **intestinal lumen** and stain variably with acid-fast staining, but the small size and surface attachment pattern in this image are more consistent with *Cryptosporidium*.

Q: Tropical pulmonary eosinophilia is specifically associated with which of the following conditions?

Occult filariasis. ***Occult filariasis*** - **Tropical pulmonary eosinophilia (TPE)** is a hypersensitivity reaction specifically caused by infection with **filarial parasites**, primarily *Wuchereria bancrofti* or *Brugia malayi*, in individuals living in endemic areas [1]. - The disease involves migration of microfilariae to the lungs, stimulating a strong **IgE-mediated immune response** leading to high eosinophil counts in the blood and lung tissue [1]. *Cerebral malaria* - **Cerebral malaria** is caused by the parasite *Plasmodium falciparum* and is characterized by neurological complications, not pulmonary eosinophilia. - It involves sequestration of parasitized red blood cells in the brain's microvasculature, leading to coma and other neurological symptoms. *Pneumonic plague* - **Pneumonic plague** is a severe bacterial infection caused by *Yersinia pestis*, affecting the lungs and leading to pneumonia. - It is not associated with eosinophilia and requires antibiotic treatment. *Asthmatic bronchitis* - **Asthmatic bronchitis** is a general term referring to inflammation of the bronchi combined with features of asthma, often triggered by allergens, irritants, or infections. - While it can involve eosinophilic inflammation, it is a broader syndrome and not specifically linked to occult filariasis in the way TPE is.

Q: Vector for transmission of sleeping sickness?

Tse-tse fly. ***Tse-tse fly*** - The **tsetse fly** (genus *Glossina*) is the exclusive biological vector for the transmission of **African trypanosomiasis**, also known as sleeping sickness. - The fly transmits the parasites (*Trypanosoma brucei*) to humans through its bite after becoming infected by feeding on an infected host. *Sandfly* - **Sandflies** (family Psychodidae) are vectors for diseases such as **leishmaniasis** and **Bartonellosis** (Carrion's disease), but not sleeping sickness. - They are typically smaller than tsetse flies and have distinct hairy bodies and wings. *Black fly* - **Black flies** (family Simuliidae) are vectors for **onchocerciasis** (river blindness), caused by the *Onchocerca volvulus* parasite. - They are characterized by their hump-backed appearance and prefer to breed in fast-flowing rivers. *Hard tick* - **Hard ticks** (family Ixodidae) are vectors for a variety of diseases, including **Lyme disease**, **Rocky Mountain spotted fever**, and **Crimean-Congo hemorrhagic fever**. - They are arachnids, not insects, and transmit pathogens through prolonged feeding.

Q: A patient presents with headache, high fever, and meningismus. Within 3 days, he becomes unconscious. What is the most probable causative agent? Refer to the image for diagnosis.

Naegleria fowleri infection. ***Naegleria fowleri infection*** - The image shows **trophozoites of *Naegleria fowleri***, characterized by their amoeboid shape and often prominent nucleolus visible within the nucleus. - The clinical presentation of rapidly progressing **headache, high fever, meningismus**, and quick deterioration to unconsciousness (within 3 days) is classic for **Primary Amoebic Meningoencephalitis (PAM)** caused by *Naegleria fowleri*. *Acanthamoeba infection* - *Acanthamoeba* causes **Granulomatous Amoebic Encephalitis (GAE)**, which typically has a more **subacute to chronic course** (weeks to months) rather than the rapid progression described. - While *Acanthamoeba* can cause CNS infections and trophozoites can be seen, the rapid clinical decline points against GAE. *Trypanosoma infection* - **African trypanosomiasis (sleeping sickness)** is caused by *Trypanosoma brucei* and features symptoms like fever, headache, and neurological signs, but its progression is usually **slower and more chronic** (weeks to months or even years) compared to the acute presentation here. - **American trypanosomiasis (Chagas disease)** can cause neurological symptoms, but it's often linked to the chronic phase of the disease or congenital infection, and the rapid progression of fulminant meningoencephalitis is not typical. *Entamoeba infection* - While *Entamoeba histolytica* can cause **amoebic liver abscesses** and, rarely, direct brain abscesses, it typically does not present as an acute, fulminant meningoencephalitis like that caused by *Naegleria fowleri*. - The morphology of *Entamoeba* trophozoites, with a single, small, central karyosome in the nucleus, also differs from the features seen in the image.

Q: Which of the following protozoan parasites does not have a cystic form in humans?

Trichomonas. ***Trichomonas*** - *Trichomonas vaginalis* exists only as a **trophozoite** form, lacking a protective cystic stage, which limits its survival outside the host. - Its transmission typically occurs directly through **sexual contact**, as it cannot survive in the environment. *E.histolytica* - *Entamoeba histolytica* forms **cysts** that are resistant to environmental conditions and are the infective stage, transmitted via the fecal-oral route. - These cysts allow the parasite to survive stomach acid and excyst in the small intestine to release trophozoites. *Giardia* - *Giardia lamblia* has a **resistant cyst form** that is responsible for environmental survival and transmission through contaminated water or food. - The cysts are hardy and can survive for extended periods, facilitating the spread of giardiasis. *Toxoplasma* - *Toxoplasma gondii* exists in various forms, including environmentally resistant **oocysts** (shed in cat feces) and **tissue cysts** found in infected meat. - These cystic forms are crucial for its transmission to humans, either through ingestion of contaminated food/water or undercooked meat.

Q: Mucocutaneous leishmaniasis is caused by which of the following?

L. braziliensis. ***L. braziliensis*** - *Leishmania braziliensis* is the primary causative agent of **mucocutaneous leishmaniasis**, particularly in the New World (Central and South America). - This form of leishmaniasis is characterized by spread from the initial skin lesion to the **mucous membranes**, leading to progressive destructive lesions of the nose, mouth, and throat (espundia). - It causes significant morbidity due to tissue destruction and disfigurement. *L. tropica* - *Leishmania tropica* is typically associated with **cutaneous leishmaniasis** (Old World cutaneous leishmaniasis). - It causes localized skin lesions, often referred to as **"oriental sore,"** but generally does not progress to mucocutaneous forms. - Endemic in Mediterranean, Middle East, and parts of Asia. *L. donovani* - *Leishmania donovani* is the primary cause of **visceral leishmaniasis**, also known as **kala-azar**. - This severe systemic form affects internal organs like the spleen, liver, and bone marrow. - It is not associated with mucocutaneous lesions and presents with fever, hepatosplenomegaly, and pancytopenia. *L. mexicana* - *Leishmania mexicana* is a cause of **cutaneous leishmaniasis** in the New World, often presenting as chronic skin ulcers. - Although it can sometimes cause diffuse cutaneous leishmaniasis, it is **not** the primary species associated with mucocutaneous leishmaniasis leading to destructive mucosal lesions. - Endemic in Mexico, Central America, and northern South America.

Q: In which disease are tachyzoites commonly observed?

Toxoplasma. ***Toxoplasma*** - **Tachyzoites** are the rapidly multiplying form of **_Toxoplasma gondii_** that are responsible for acute infection and tissue damage. - They are commonly observed during the active phase of **toxoplasmosis**, especially in immunosuppressed individuals or during congenital infection. *Toxocara* - **Toxocara** species (e.g., **_Toxocara canis_**) cause toxocariasis, characterized by the migration of larval forms, not tachyzoites, through host tissues. - The diagnosis of **toxocariasis** is typically made by serology detecting antibodies to larval antigens. *Pulmonary eosinophilia* - **Pulmonary eosinophilia** is a syndrome characterized by an abnormal accumulation of **eosinophils** in the lungs, often due to parasitic infections (e.g., Strongyloides, ascaris) or allergic reactions. - It is a host response and does not involve the observation of specific parasitic forms like tachyzoites in the lung tissue itself. *Ascaris* - **Ascaris lumbricoides** is a large intestinal nematode that causes ascariasis; its life cycle involves eggs, larval stages (passed in feces), and adult worms. - The disease is diagnosed by finding **ova in stool samples** or observing adult worms, not tachyzoites.

Q: A patient presents with fever. Peripheral smear shows band across the erythrocytes. What is the diagnosis?

P. malariae. ***P. malariae*** - The presence of a **band across the erythrocytes** on a peripheral smear is a classic morphological feature of the **trophozoite stage of *Plasmodium malariae***. - This characteristic "band form" helps distinguish *P. malariae* from other *Plasmodium* species. *P. falciparum* - Characteristically presents with **ring forms** and **gametocytes (banana-shaped)** in red blood cells on peripheral smears. - It does not typically form **bands across erythrocytes**. *P. vivax* - Known for forming large, amoeboid trophozoites and schizonts in **enlarged red blood cells** with **Schüffner's dots**. - It does not exhibit the specific "band form" seen in *P. malariae*. *P. ovale* - Infestations often present with **oval-shaped erythrocytes** and contain **Schüffner's dots**. - While it has some similarities to *P. vivax*, it does not show the distinctive band form on the smear.

Q: Which worm causes myocarditis?

Trichinella. ***Trichinella*** - **Trichinella spiralis** larvae can encyst in muscle tissue, including the myocardium, leading to **inflammation** and **myocarditis** in severe cases. - This parasitic infection is acquired by consuming **undercooked meat**, especially pork, containing larvae. *Enterobius* - **Enterobius vermicularis**, or pinworm, primarily causes **pruritus ani** and does not typically invade cardiac muscle. - Its life cycle is confined to the **gastrointestinal tract** and perianal region. *Strongyloides* - **Strongyloides stercoralis** can cause a range of symptoms, from cutaneous larva currens to hyperinfection syndrome, but **myocarditis** is not a typical manifestation. - It primarily affects the **gastrointestinal tract**, lungs, and skin. *Trichuris* - **Trichuris trichiura**, or whipworm, mainly causes **colitis** and **rectal prolapse** in heavy infections. - It remains in the **large intestine** and does not usually disseminate to cause myocarditis.

Q: A lady from West Rajasthan presented with an ulcer surrounded by erythema on the right leg. Microscopy of the biopsy from the edge of the ulcer showed organisms with dark staining nuclei and kinetoplast. What is the most likely causative agent? (Refer to the provided image)

Leishmania tropica. ***Leishmania tropica*** - The presence of an ulcer with surrounding erythema in **West Rajasthan**, along with microscopy showing organisms with a **nucleus and kinetoplast**, is highly characteristic of **cutaneous leishmaniasis** caused by *Leishmania tropica*. - The organisms seen are **amastigotes** within macrophages in skin lesions, which are identified by their distinct **nucleus and kinetoplast** on microscopy. - West Rajasthan is an **endemic area** for cutaneous leishmaniasis. *Babesia microti* - *Babesia microti* causes **babesiosis**, a tick-borne illness affecting red blood cells, leading to **hemolytic anemia** and malaria-like symptoms. - It does not typically cause **skin ulcers** and its characteristic form in smears is a **ring form or tetrad ("Maltese cross")** within red blood cells, not organisms with kinetoplasts in macrophages. *Trypanosoma brucei* - *Trypanosoma brucei* causes **African trypanosomiasis (sleeping sickness)**, presenting with fever, headaches, joint pain, and neurological symptoms, possibly a **chancre** at the inoculation site. - While it has a **kinetoplast**, it exists as a flagellated **trypomastigote** in the blood and CSF, not as an **amastigote** in macrophages within a skin ulcer. - Additionally, this is **geographically incorrect** for West Rajasthan. *Histoplasma capsulatum* - *Histoplasma capsulatum* is a **fungus** that causes **histoplasmosis**, primarily affecting the respiratory system, especially in immunocompromised individuals. - It does **not possess a kinetoplast** and while it can cause disseminated disease with skin lesions, the microscopic appearance would be **yeast forms** within macrophages, not organisms with kinetoplasts.

Question 1

A 52-year-old male with HIV presents with profuse, watery diarrhea of 5 days’ duration. A biopsy of the small intestine is shown here. What is the most likely cause of this patient’s symptoms?

Accepted Answer

Cryptosporidium spp.

Answer

Giardia lamblia

Answer

Cystoisospora belli

Answer

Cyclospora cayetanensis

Question 2

Tropical pulmonary eosinophilia is specifically associated with which of the following conditions?

Accepted Answer

Occult filariasis

Answer

Asthmatic bronchitis

Answer

Pneumonic plague

Answer

Cerebral malaria

Question 3

Vector for transmission of sleeping sickness?

Accepted Answer

Tse-tse fly

Answer

Sandfly

Answer

Black fly

Answer

Hard tick

Question 4

A patient presents with headache, high fever, and meningismus. Within 3 days, he becomes unconscious. What is the most probable causative agent? Refer to the image for diagnosis.

Accepted Answer

Naegleria fowleri infection

Answer

Acanthamoeba infection

Answer

Trypanosoma infection

Answer

Entamoeba infection

Question 5

Which of the following protozoan parasites does not have a cystic form in humans?

Accepted Answer

Trichomonas

Answer

E.histolytica

Answer

Giardia

Answer

Toxoplasma

Question 6

Mucocutaneous leishmaniasis is caused by which of the following?

Accepted Answer

L. braziliensis

Answer

L. tropica

Answer

L. donovani

Answer

L. mexicana

Question 7

In which disease are tachyzoites commonly observed?

Accepted Answer

Toxoplasma

Answer

Toxocara

Answer

Pulmonary eosinophilia

Answer

Ascaris

Question 8

A patient presents with fever. Peripheral smear shows band across the erythrocytes. What is the diagnosis?

Accepted Answer

P. malariae

Answer

P. falciparum

Answer

P. vivax

Answer

P. ovale

Question 9

Which worm causes myocarditis?

Accepted Answer

Trichinella

Answer

Enterobius

Answer

Strongyloides

Answer

Trichuris

Question 10

A lady from West Rajasthan presented with an ulcer surrounded by erythema on the right leg. Microscopy of the biopsy from the edge of the ulcer showed organisms with dark staining nuclei and kinetoplast. What is the most likely causative agent? (Refer to the provided image)

Accepted Answer

Leishmania tropica

Answer

Babesia microti

Answer

Trypanosoma brucei

Answer

Histoplasma capsulatum

Parasitology — MCQs

Parasitology — MCQs

On this page

Practice by Chapter

Want unlimited practice?