Parasitology Practice Questions

Q: A 35-year-old heterosexual patient diagnosed with HIV had a history of chronic watery diarrhea. A colonoscopic biopsy is shown below. What is the most probable diagnosis?

Cryptosporidiosis. ***Cryptosporidiosis*** - The image likely shows **intracellular but extracytoplasmic organisms attached to the apical brush border** on the luminal surface of the intestinal epithelium, consistent with *Cryptosporidium parvum*. - In an HIV-positive patient with **chronic watery diarrhea**, cryptosporidiosis is a common and often severe opportunistic infection. *Giardiasis* - Caused by *Giardia lamblia*, which typically presents as **trophozoites or cysts** in the stool or duodenum, not usually as intracellular organisms. - While it can cause chronic diarrhea, the characteristic biopsy findings would differ significantly. *Cytomegalovirus (CMV) infection* - CMV colitis presents with characteristic large **intranuclear and intracytoplasmic inclusions** within infected cells, often with associated inflammation and ulceration. - While CMV is common in HIV, the described image is more suggestive of a parasitic infection. *Microsporidiosis* - Microsporidia are also **intracellular parasites** that can cause chronic diarrhea in HIV patients and are very small (1-4 µm). - However, they are typically much **smaller than Cryptosporidium** and require specialized stains (e.g., modified trichrome) to be easily visualized, and the image provided is more typical of *Cryptosporidium*.

Q: Identify the organism related to the blood smear image.

Plasmodium falciparum. ***Plasmodium falciparum*** - This organism is characterized by **delicate, ring-form trophozoites** and occasionally **banana-shaped gametocytes** in red blood cells. - The presence of multiple rings per red blood cell and **applique forms** (rings on the periphery of the red blood cell) is highly suggestive of *P. falciparum* infection. - Blood smears showing **high parasitemia** with predominantly ring forms are strongly suggestive of *P. falciparum* malaria, particularly when combined with multiple delicate rings per erythrocyte, appliqué forms, normal-sized erythrocytes, and characteristic gametocytes when present. *Salmonella Typhi* - This is a **gram-negative bacterium** that causes typhoid fever, primarily affecting the gastrointestinal tract. - It does not present as **intraerythrocytic parasites** on a blood smear. - Diagnosis is made through **blood culture** or bone marrow culture, not blood smear microscopy. *Toxoplasma gondii* - This is an **obligate intracellular parasite** that typically forms **tissue cysts** (e.g., brain, muscle) and is not found as intraerythrocytic forms. - Tachyzoites may be seen in blood in acute infection, but appear as **free extracellular** or intracellular forms in leukocytes, not within red blood cells. - Diagnosis is typically via **serology** or PCR, not routine blood smear examination. *Treponema pallidum* - This is a **spirochete bacterium** responsible for syphilis. - It is too thin to be seen on routine blood smears and is typically identified using **dark-field microscopy** or **serological tests** (VDRL, RPR, TPPA). - Does not appear as intraerythrocytic forms on blood smear.

Q: Sabin Feldman dye test is used for diagnosis of which of the following condition?

Toxoplasmosis. ***Toxoplasmosis*** The **Sabin-Feldman dye test** is a **serological assay** used to detect specific IgG antibodies against *Toxoplasma gondii*, the causative agent of toxoplasmosis. It measures the ability of antibodies in a patient's serum to prevent the cytoplasmic staining of live toxoplasma tachyzoites by methylene blue dye, indicating an **active immune response** to the parasite. This classic test has high sensitivity and specificity for detecting toxoplasma antibodies and is considered the gold standard serological test, though it has been largely replaced by ELISA and IFA in routine practice due to the requirement for live organisms. *Botulism* Botulism is diagnosed through **toxin detection** in serum, stool, or food samples using mouse bioassay, or by culturing *Clostridium botulinum* from clinical specimens. The Sabin-Feldman dye test is not relevant for the diagnosis of botulism, which is a **neuroparalytic disease** caused by botulinum neurotoxin blocking acetylcholine release at neuromuscular junctions. *Sarcoidosis* Sarcoidosis is a multisystem **granulomatous disease** diagnosed primarily by **tissue biopsy** showing non-caseating granulomas along with compatible clinical and radiological findings. Supportive tests include elevated serum ACE levels and Kveim test (historical). There is no serological test like the Sabin-Feldman dye test associated with the diagnosis of sarcoidosis, as it is not an infectious disease requiring antibody detection. *Yellow fever* Yellow fever is a **viral hemorrhagic disease** caused by a flavivirus, diagnosed by detecting viral RNA through RT-PCR or specific IgM antibodies in the acute phase of infection using ELISA or immunofluorescence. The Sabin-Feldman dye test is not used for viral infections like yellow fever, as it specifically targets **toxoplasma antibodies** and has no role in arboviral disease diagnosis.

Q: Pulmonary eosinophilia is found in infection with ?

Strongyloides. ***Strongyloides*** - **Strongyloides stercoralis** can cause **pulmonary eosinophilia** (Löffler's syndrome) as larvae migrate through the lungs [1]. - This migration is part of the parasite's life cycle, leading to an inflammatory response with eosinophil infiltration [1]. *Babesia* - **Babesia** species primarily infect **red blood cells** and cause **hemolytic anemia**, resembling malaria. - They are transmitted by ticks and do not typically cause pulmonary eosinophilia. *Malaria* - **Malaria**, caused by Plasmodium parasites, is known for infecting **red blood cells** and causing cyclical fevers, chills, and anemia. - It does not typically present with pulmonary eosinophilia as a characteristic feature. *Trypanosoma* - **Trypanosoma** species cause **sleeping sickness** (African trypanosomiasis) and **Chagas disease** (American trypanosomiasis). - These infections affect the bloodstream, lymphatic system, and various organs, but pulmonary eosinophilia is not a hallmark.

Q: Which of the following is the causative organism of Acanthamoeba keratitis?

Acanthamoeba. ***Acanthamoeba*** - **Acanthamoeba keratitis** is a serious and painful infection of the eye's cornea caused by species of the **free-living amoeba Acanthamoeba**. - This infection is commonly associated with contact lens wear, particularly when proper hygiene and disinfection practices are not followed. *Plasmodium* - **Plasmodium** species are the causative agents of **malaria**, a mosquito-borne infectious disease affecting red blood cells and the liver. - It does not cause eye infections like keratitis and is transmitted through the bite of an infected Anopheles mosquito. *Toxoplasma* - **Toxoplasma gondii** is an intracellular parasitic protozoon that causes **toxoplasmosis**, which can manifest as chorioretinitis, encephalitis, or lymphadenopathy. - While it can affect the eye (**ocular toxoplasmosis**), it causes retinitis or chorioretinitis, not keratitis. *W. bancrofti* - **Wuchereria bancrofti** is a filarial nematode that causes **lymphatic filariasis**, an infection leading to elephantiasis and other lymphatic disorders. - It primarily affects the lymphatic system and subcutaneous tissues, not the cornea.

Q: Which stage of Leishmania is found in spleen aspirate of a patient?

Amastigote stage. ***Amastigote stage*** - The **amastigote stage** is the **intracellular, non-flagellated form** of Leishmania that replicates within **macrophages** of the vertebrate host, including humans. - In visceral leishmaniasis, these **amastigotes** are abundant in organs like the **spleen**, liver, and bone marrow, making them detectable in spleen aspirates. *Promastigote stage* - The **promastigote stage** is the **extracellular, flagellated form** of Leishmania found in the digestive tract of the **sand fly vector**. - It is typically **not found** in human tissues or spleen aspirates. *Epimastigote stage* - The **epimastigote stage** is a flagellated form of **trypanosomes** (e.g., *Trypanosoma cruzi*) but **not Leishmania**. - It is found in the **vector's gut** for trypanosomes and is not part of the Leishmania life cycle in humans. *Trypomastigote stage* - The **trypomastigote stage** is another flagellated form characteristic of **trypanosomes** (e.g., *Trypanosoma cruzi* and *Trypanosoma brucei*). - It circulates in the **blood of the vertebrate host** for trypanosomes and is not observed in Leishmania infections within human organs like the spleen.

Q: How is diagnosis of filariasis confirmed most commonly?

Detection of microfilariae. ***Detection of microfilariae*** - The most common and definitive method for diagnosing active filariasis is by identifying **microfilariae** in **peripheral blood smears**. - **Nocturnal periodicity** sampling (collection between 10 PM and 2 AM) is often crucial for detecting *Wuchereria bancrofti* and *Brugia malayi* due to their migratory patterns. *Clinical features* - While clinical symptoms like **lymphadenopathy**, **lymphedema**, and **hydrocele** are highly suggestive, they are often late manifestations and can overlap with other conditions. - Clinical features alone are not sufficient for a definitive diagnosis, as other diseases can present similarly, and they do not confirm the presence of live parasites. *PCR* - **PCR (Polymerase Chain Reaction)** methods are highly sensitive and specific for detecting parasite DNA, even at low parasite loads, and can differentiate between species. - Though very useful, especially for **occult infections** or low parasitemia, PCR is usually considered a more advanced or research-oriented diagnostic tool rather than the most common initial confirmation method. *Serological test* - **Serological tests** detect **antibodies** (e.g., IgG4) against filarial antigens, indicating exposure to the parasite. - These tests are valuable in endemic areas, for screening, and in cases of **amicrofilaremic infections**, but they cannot distinguish between past and active infections and may lack sensitivity in early stages.

Q: What is a distinguishing feature of E. histolytica compared to E. dispar?

Ingestion of red blood cells by trophozoites. ***Ingestion of red blood cells by trophozoites*** - **E. histolytica** is a pathogenic amoeba that invades intestinal mucosa and is **hematophagous** (ingests RBCs) - The presence of **ingested erythrocytes within trophozoites** is a key distinguishing feature that suggests *E. histolytica* rather than *E. dispar* - *E. dispar* is **non-pathogenic** and does not typically ingest RBCs, as it does not invade tissues - While not 100% specific (some E. histolytica may not show RBCs, and molecular methods are gold standard), **finding RBCs in trophozoites is clinically significant** for differentiating these morphologically identical species *Presence of cysts with 1-4 nuclei* - Both *E. histolytica* and *E. dispar* form cysts with **1-4 nuclei** with identical morphology - The cyst stages of these two species are **morphologically indistinguishable** under light microscopy - This feature **cannot be used** to differentiate between the two species *Presence of pseudopodia* - Both species are amoebae and possess **pseudopodia** for motility during the trophozoite stage - This is a **general characteristic of all amoebae** and does not distinguish these species *Presence of blunt pseudopodia* - Both *E. histolytica* and *E. dispar* produce **blunt, finger-like pseudopodia** for movement - The pseudopodial morphology is **identical in both species** and cannot be used for differentiation

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*.

Question 1

A 35-year-old heterosexual patient diagnosed with HIV had a history of chronic watery diarrhea. A colonoscopic biopsy is shown below. What is the most probable diagnosis?

Accepted Answer

Cryptosporidiosis

Answer

Giardiasis

Answer

Cytomegalovirus (CMV) infection

Answer

Microsporidiosis

Question 2

Identify the organism related to the blood smear image.

Accepted Answer

Plasmodium falciparum

Answer

Salmonella Typhi

Answer

Toxoplasma gondii

Answer

Treponema pallidum

Question 3

Sabin Feldman dye test is used for diagnosis of which of the following condition?

Accepted Answer

Toxoplasmosis

Answer

Botulism

Answer

Sarcoidosis

Answer

Yellow fever

Question 4

Pulmonary eosinophilia is found in infection with ?

Accepted Answer

Strongyloides

Answer

Babesia

Answer

Malaria

Answer

Trypanosoma

Question 5

Which of the following statements about amoebiasis is correct?

Accepted Answer

Amoebic liver abscess occurs in 10% of intestinal amoebiasis cases in tropical regions

Answer

The abscess wall provides the highest yield for Entamoeba histolytica culture

Answer

The portal circulation prevents systemic spread of Entamoeba histolytica

Answer

Amoebic liver abscesses are formed primarily due to bacterial suppuration

Question 6

Which of the following is the causative organism of Acanthamoeba keratitis?

Accepted Answer

Acanthamoeba

Answer

Plasmodium

Answer

Toxoplasma

Answer

W. bancrofti

Question 7

Which stage of Leishmania is found in spleen aspirate of a patient?

Accepted Answer

Amastigote stage

Answer

Promastigote stage

Answer

Epimastigote stage

Answer

Trypomastigote stage

Question 8

How is diagnosis of filariasis confirmed most commonly?

Accepted Answer

Detection of microfilariae

Answer

Clinical features

Answer

PCR

Answer

Serological test

Question 9

What is a distinguishing feature of E. histolytica compared to E. dispar?

Accepted Answer

Ingestion of red blood cells by trophozoites

Answer

Presence of pseudopodia

Answer

Presence of blunt pseudopodia

Answer

Presence of a thin nuclear membrane

Question 10

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

Parasitology — MCQs

Parasitology — MCQs

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