Parasitology Practice Questions

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: 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: 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 parasites is typically identified using the modified Ziehl-Neelsen (ZN) stain?

Isospora. ***Isospora*** - The modified **Ziehl-Neelsen (ZN) stain** is specifically used to identify **acid-fast organisms**, and *Isospora* (now generally referred to as *Cystoisospora*) oocysts retain the stain, appearing pink to red. - This staining characteristic distinguishes it from other parasites that do not exhibit acid-fast properties, making it a key diagnostic tool for coccidian parasites. *Microsporidia* - While *Microsporidia* are also intestinal parasites, they are typically identified using specialized stains such as **chromotrope stains** or **fluorescent brighteners** (e.g., Uvitex 2B) due to their small size and unique spore structure. - They do not consistently stain well with the modified ZN method, which is designed for detecting acid-fast structures. *Plasmodium* - *Plasmodium* species are the causative agents of malaria and are identified primarily by examining **Giemsa-stained blood smears**, where their various stages (trophozoites, schizonts, gametocytes) are visible within red blood cells. - The modified ZN stain is not used for the diagnosis of malaria as *Plasmodium* parasites are not acid-fast. *Echinococcus* - *Echinococcus* causes **hydatid disease**, and diagnosis typically involves imaging techniques (e.g., ultrasound, CT, MRI) to visualize **cysts** in organs, serological tests for antibodies, and microscopic examination of cyst fluid for **protoscolices** or **hooklets**. - The modified ZN stain is not relevant for identifying *Echinococcus* as it is a cestode (tapeworm) and does not possess acid-fast properties in a diagnostic context.

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 boy presented with a fever and chills. Rapid test was positive for specific antigen HRP-2. Which of the following species of Plasmodium is the most likely causative agent?

Plasmodium falciparum. ***Plasmodium falciparum*** - The **histidine-rich protein 2 (HRP-2)** antigen is specifically produced by **P. falciparum** and is targeted by most rapid diagnostic tests for malaria. - A positive HRP-2 test in a patient with fever and chills indicates a high likelihood of **P. falciparum** infection, which is often the most severe form of malaria. *Plasmodium malariae* - **P. malariae** does not produce **HRP-2 antigen**, therefore, a rapid diagnostic test targeting HRP-2 would be negative for this species. - This species can cause a **quartan fever pattern** (fever every 72 hours) and usually presents with less severe symptoms compared to P. falciparum. *Plasmodium vivax* - **P. vivax** produces **_Plasmodium_ lactate dehydrogenase (pLDH)** and **aldolase antigens**, but not HRP-2. Some rapid tests combine detection of HRP-2 with pLDH to identify both *P. falciparum* and *P. vivax*. - While *P. vivax* causes fever and chills, its presence would not be indicated by a positive HRP-2 specific test alone. *Plasmodium ovale* - **P. ovale** also produces **pLDH and aldolase antigens**, similar to *P. vivax*, and does not produce **HRP-2**. - Infections with *P. ovale* are relatively rare and generally cause milder disease than *P. falciparum*, often with a **tertian fever pattern**.

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.

Q: Identify the parasite shown in the image.

Trichuris trichiura. ***Trichuris trichiura*** - The image displays characteristic **lemon-shaped** or **barrel-shaped eggs** with distinctive **polar plugs** at each end, which are pathognomonic for *Trichuris trichiura* (whipworm) eggs. - These eggs are thick-shelled and typically measure 50-55 µm by 20-25 µm, containing an undeveloped larva when passed in feces. *Ancylostoma duodenale* - Eggs of *Ancylostoma duodenale* (Old World hookworm) are **oval-shaped** with blunt ends, and a **thin shell**. - They typically contain a **segmented ovum** or an early-stage larva, lacking the polar plugs seen in the image. *Paragonimus westermani* - *Paragonimus westermani* (lung fluke) eggs are generally **oval-shaped** with a **flattened operculum** at one end, which is not visible in the image. - They are larger than *Trichuris* eggs, often measuring around 80-120 µm by 45-70 µm, and are often coughed up in sputum or passed in feces. *Strongyloides stercoralis* - *Strongyloides stercoralis* primarily produces **larvae** (rhabditiform or filariform) in stool samples rather than eggs. - If eggs are seen (rarely, in cases of severe diarrhea), they are small, thin-shelled, and typically contain a developed larva, unlike the eggs shown.

Q: A 15-year-old boy presented with fever and chills for 3 days. On examination, he was found to have delayed skin pinch time and dry oral mucosa. A peripheral blood smear revealed multiple delicate ring forms within red blood cells, with some red blood cells containing more than one ring form. No other developmental stages were observed. Identify the pathogen involved.

Plasmodium falciparum. ***Plasmodium falciparum*** - The presence of **multiple delicate ring forms** with **multiply infected red blood cells** (more than one ring per RBC) on peripheral blood smear is characteristic of *Plasmodium falciparum* infection. - A key distinguishing feature of *P. falciparum* is that **only ring forms** are typically seen in peripheral blood due to **sequestration of mature stages** (trophozoites and schizonts) in deep capillaries of internal organs. - The clinical presentation with fever, chills, and signs of dehydration is consistent with falciparum malaria, which can progress to severe complications. *Plasmodium vivax* - *Plasmodium vivax* also causes malaria and shows ring forms, but typically presents with **enlarged red blood cells** (due to preferential infection of reticulocytes) and **all developmental stages visible** in peripheral blood, including trophozoites, schizonts, and gametocytes. - The absence of enlarged RBCs and other developmental stages, combined with multiply infected cells, makes *P. vivax* less likely. *Babesia* - While **Babesia** also infects red blood cells and can show ring forms, its characteristic finding is **pear-shaped trophozoites** arranged in **tetrads (Maltese cross appearance)**. - **Babesiosis** is typically transmitted by ticks and is more common in immunocompromised individuals or in specific geographic regions (e.g., northeastern United States). *Salmonella typhi* - **Salmonella typhi** causes **typhoid fever**, which presents with prolonged fever, headache, and gastrointestinal symptoms, but it is a **bacterial infection** and does not involve infection of red blood cells. - Diagnosis is made by **blood culture** or **bone marrow culture**, not by microscopic examination of red blood cells for parasites.

Question 1

In which disease are tachyzoites commonly observed?

Accepted Answer

Toxoplasma

Answer

Toxocara

Answer

Pulmonary eosinophilia

Answer

Ascaris

Question 2

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 3

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 4

Which of the following parasites is typically identified using the modified Ziehl-Neelsen (ZN) stain?

Accepted Answer

Isospora

Answer

Microsporidia

Answer

Plasmodium

Answer

Echinococcus

Question 5

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 6

Which worm causes myocarditis?

Accepted Answer

Trichinella

Answer

Enterobius

Answer

Strongyloides

Answer

Trichuris

Question 7

A boy presented with a fever and chills. Rapid test was positive for specific antigen HRP-2.    Which of the following species of Plasmodium is the most likely causative agent?

Accepted Answer

Plasmodium falciparum

Answer

Plasmodium malariae

Answer

Plasmodium vivax

Answer

Plasmodium ovale

Question 8

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

Question 9

Identify the parasite shown in the image.

Accepted Answer

Trichuris trichiura

Answer

Ancylostoma duodenale

Answer

Strongyloides stercoralis

Answer

Paragonimus westermani

Question 10

A 15-year-old boy presented with fever and chills for 3 days. On examination, he was found to have delayed skin pinch time and dry oral mucosa. A peripheral blood smear revealed multiple delicate ring forms within red blood cells, with some red blood cells containing more than one ring form. No other developmental stages were observed. Identify the pathogen involved.

Accepted Answer

Plasmodium falciparum

Answer

Babesia

Answer

Salmonella typhi

Answer

Plasmodium vivax

Parasitology — MCQs

Parasitology — MCQs

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