Parasitology Practice Questions

Q: Which of the following statements is true about hydatid disease?

It is a zoonosis. ***Correct: It is a zoonosis*** - Hydatid disease is caused by the larval stage of **Echinococcus granulosus**, a **tapeworm**, and is transmitted from animals to humans - **Zoonoses** are diseases that can be transmitted from animals to humans, making this the correct statement - The primary reservoir includes dogs (definitive hosts) and sheep (intermediate hosts), with transmission to humans occurring through contact with contaminated dog feces *Incorrect: It is a protozoal disease* - Hydatid disease is caused by a **tapeworm** (cestode), specifically *Echinococcus granulosus*, not by a protozoan - Protozoal diseases are caused by single-celled eukaryotic organisms such as *Plasmodium* (malaria) or *Giardia* (giardiasis) - This is a helminthic infection, not a protozoal one *Incorrect: Man is the definitive host* - In the life cycle of *Echinococcus granulosus*, **dogs and other canines** are the **definitive hosts**, harboring the adult tapeworm in their intestines - Humans are **accidental intermediate hosts**, getting infected by ingesting eggs and developing hydatid cysts in organs (especially liver and lungs) - The natural cycle involves dogs eating infected offal from sheep, not humans being part of the natural transmission cycle *Incorrect: It is rare in sheep rearing countries* - Hydatid disease is **endemic** and more common in **sheep-rearing countries** including Mediterranean regions, Middle East, South America, Australia, and parts of Africa - Sheep act as important intermediate hosts in the life cycle of *Echinococcus granulosus* - The dog-sheep-dog cycle maintains high endemicity in pastoral communities where dogs have access to infected sheep viscera

Q: A female presents with dysuria and vaginal discharge. Wet mount examination shows pear-shaped organisms. What is the most likely diagnosis?

Trichomonas. ***Trichomonas*** - The presence of **dysuria**, **vaginal discharge**, and **pear-shaped organisms** on wet mount examination is classic for **Trichomonas vaginalis** infection. - **Microscopic identification of motile trichomonads** confirms the diagnosis. *Candida* - **Candida** infections typically present with **thick, white, curd-like vaginal discharge**, and a wet mount would show **yeast buds or pseudohyphae**, not pear-shaped organisms. - While it can cause dysuria, the discharge characteristics and microscopy findings differentiate it. *Chlamydia* - **Chlamydia trachomatis** causes **mucopurulent cervicitis** with dysuria and vaginal discharge, but requires **specific diagnostic tests** such as **NAAT (nucleic acid amplification test)** or cell culture for diagnosis. - Wet mount examination would **not show pear-shaped organisms**; instead, it may show increased white blood cells but no specific pathogen visualization. *Bacterial vaginosis* - **Bacterial vaginosis** is characterized by a **thin, gray discharge** and a **"fishy" odor**, which is especially noticeable after intercourse. - Wet mount shows **clue cells** (vaginal epithelial cells studded with bacteria), not pear-shaped organisms, and **absent or few white blood cells**.

Q: Which of the following is TRUE about screening for Trichomonas vaginalis?

NAAT is recommended for screening high-risk women. ***NAAT is recommended for screening high-risk women*** - **Nucleic Acid Amplification Tests (NAATs)** are highly sensitive and specific for detecting *Trichomonas vaginalis*, making them the preferred method for screening in high-risk populations due to their superior performance over traditional methods. - Screening high-risk women (e.g., those with multiple sexual partners, other STIs, or in areas with high prevalence) with NAATs helps in early detection and treatment, which is crucial for preventing further transmission and complications. *Urine samples are inadequate for testing* - **Urine samples** can indeed be used for *Trichomonas vaginalis* testing, particularly with NAATs, as they provide an alternative to vaginal swabs and are often preferred for their ease of collection and non-invasiveness. - While less sensitive than vaginal swabs for microscopy or culture, **NAATs performed on urine** have good sensitivity and specificity, making them a common option. *Culture is no longer used for diagnosis* - **Culture (e.g., InPouch TV system)** is still considered a **gold standard** for *Trichomonas vaginalis* diagnosis due to its high sensitivity and ability to detect viable organisms, especially when NAATs are not available or for confirming ambiguous results. - It is particularly useful in cases where organisms are present in low numbers or in settings where resources for advanced molecular testing are limited, though it is **less rapid** than NAATs. *Wet mount microscopy has sensitivity >95%* - **Wet mount microscopy** is an inexpensive and rapid diagnostic method, but its sensitivity for detecting *Trichomonas vaginalis* is **relatively low**, typically ranging from **50-70%**, not >95%. - The sensitivity of wet mounts is highly dependent on the **operator's skill**, the concentration of organisms, and the time elapsed since sample collection, making it prone to false negatives.

Q: How does trichomoniasis affect HIV transmission?

By increasing HIV viral shedding from genital tract. ***By increasing HIV viral shedding from genital tract*** - **Trichomoniasis** causes inflammation and disruption of the **genital mucosal barrier**, leading to an increased concentration of HIV in genital secretions. - This elevated **viral load** in the genital tract directly increases the likelihood of HIV transmission during sexual contact. *By selection for drug-resistant HIV strains* - This mechanism is not directly associated with **trichomoniasis**; drug resistance typically develops due to suboptimal adherence to antiretroviral therapy (ART) or drug mutations. - **Trichomoniasis** does not exert selective pressure on HIV to develop drug resistance. *By direct activation of HIV transcription* - While other co-infections can activate immune cells and enhance HIV replication, the primary mechanism of **trichomoniasis** enhancing HIV transmission is through increased shedding, rather than direct transcriptional activation. - **Trichomoniasis**-induced inflammation creates a fertile environment for immune cells, which in turn can become targets for HIV, but direct transcription activation is not its main role. *By inhibiting host macrophage function* - **Trichomoniasis** is primarily associated with immune system activation and inflammation, rather than significant inhibition of **macrophage function**. - Impaired macrophage function would more likely decrease, rather than increase, viral dissemination or immune response.

Q: A young boy who used to wash his contact lenses in tap water or with unhygienic lens fluid developed keratitis. Microscopy revealed an organism with spiked or star-shaped structures. Identify the correct organism responsible.

Acanthamoeba. ***Acanthamoeba*** - *Acanthamoeba* is a **free-living amoeba** found in water, soil, and inadequately disinfected contact lens solutions, specifically linked to **keratitis** in contact lens wearers. - Its characteristic morphology, often described as having **spiked or star-shaped structures**, refers to the **acanthopodia** (spine-like pseudopods) that are distinctive features visible microscopically. *Balantidium* - *Balantidium coli* is a **ciliated protozoan** and primarily causes **intestinal infections** (balantidiasis), not keratitis. - It would be distinguished microscopically by its **large size**, **kidney-shaped macronucleus**, and **cilia**, not spiked structures. *Pseudomonas* - *Pseudomonas aeruginosa* is a **bacterium** and a common cause of **bacterial keratitis**, especially in contact lens wearers, but it is not a protozoan. - Microscopically, it would appear as **rod-shaped bacteria**, not organisms with spiked or star-shaped structures. *Staphylococcus aureus* - *Staphylococcus aureus* is a **bacterium** and a frequent cause of various infections, including **bacterial keratitis**. - Under a microscope, it presents as **Gram-positive cocci in clusters**, not as an amoeba with spiked or star-shaped protrusions.

Q: A woman presents with a chronic history of fever and lower limb swelling. The microscopic image of a parasite in her blood smear is shown. Identify the pathogen responsible for her condition.

Brugia. ***Brugia*** - The image shown represents a microfilaria with **two distinct nuclei in the tail**, which is a characteristic morphological feature of *Brugia malayi* or *Brugia timori*. - *Brugia* species cause **lymphatic filariasis**, leading to chronic conditions like **fever** and **lymphatic obstruction** (lower limb swelling), consistent with the patient's presentation. *Mansonella* - *Mansonella* microfilariae typically have a **sheathless appearance** and their nuclei arrangement in the tail does not usually present as two distinct nuclei. - While *Mansonella* can cause symptoms like fever, it typically does not lead to severe **lymphatic pathology** and swelling of the extremities like *Brugia* or *Wuchereria*. *Wuchereria bancrofti* - *Wuchereria bancrofti* microfilariae are **sheathed** and their **tail nuclei are numerous** and extend to the tip, forming an indistinct pattern, unlike the distinct two nuclei seen. - This parasite also causes lymphatic filariasis but the microscopic morphology of its microfilaria differs from the image. *Loa loa* - *Loa loa* microfilariae are **sheathed**, but their distinguishing feature is the **nuclei extending to the tip of the tail** in a continuous, often wavy, column. - This parasite is known for causing **Calabar swellings** and migration across the conjunctiva, which are different clinical manifestations from chronic lower limb swelling.

Q: A child presented with perianal itching. The swab specimen is shown in the image. What is the diagnosis?

Enterobius. ***Enterobius*** - The image shows **D-shaped** (plano-convex) and **transparent eggs**, which are characteristic of *Enterobius vermicularis* (**pinworm** or **threadworm**). - **Perianal itching**, especially at night, is the hallmark symptom due to the female worm migrating to the perianal region to lay eggs. *Ascaris* - *Ascaris lumbricoides* eggs are typically **round to oval**, with a thick, mamillated (bumpy) outer shell, or smooth in the case of decorticated eggs, which is different from the eggs pictured. - Infection with *Ascaris* can cause pulmonary symptoms (Loeffler's syndrome) and intestinal obstruction, but not typically perianal itching. *Trichiura* - *Trichuris trichiura* (**whipworm**) eggs are distinctly **barrel-shaped** with prominent **polar plugs** at each end, which is not seen in the image. - Whipworm infection is often associated with bloody diarrhea, rectal prolapse, and growth retardation, not primarily perianal itching. *Ancylostoma* - *Ancylostoma duodenale* and *Necator americanus* (hookworms) eggs are typically **oval** with a **thin shell** and segmented embryo (morula stage) within, which lacks the distinct D-shape and transparency of the pictured eggs. - Hookworm infection primarily causes iron-deficiency anemia and can lead to cutaneous larva migrans, not perianal itching as a primary symptom.

Q: What is the vector for Leishmania, a parasite characterized by a prominent kinetoplast in its morphological forms?

Sand fly. ***Sand fly*** - **Sand flies** (genus *Phlebotomus* in the Old World and *Lutzomyia* in the New World) are the biological vectors responsible for transmitting *Leishmania* parasites to humans and other mammals. - The parasite exists in two main forms; the **promastigote** (flagellated) in the sand fly gut and the **amastigote** (non-flagellated) within host macrophages. *Female Anopheles Mosquito* - The **female Anopheles mosquito** is the primary vector for **malaria**, caused by *Plasmodium* parasites, and not *Leishmania*. - *Plasmodium* also undergoes sporogonic development in the mosquito, but it does not have a prominent kinetoplast in its mature forms. *Triatomine bug* - The **triatomine bug**, also known as the "kissing bug", is the vector for **Chagas disease**, caused by *Trypanosoma cruzi*. - While *Trypanosoma cruzi* is also a hemoflagellate with a kinetoplast, it is associated with different disease manifestations and geographical distribution than *Leishmania*. *TseTse fly* - The **tsetse fly** (genus *Glossina*) is the vector responsible for transmitting **African Trypanosomiasis**, or sleeping sickness, caused by *Trypanosoma brucei*. - Like *Leishmania*, *Trypanosoma brucei* also possesses a kinetoplast, but it causes a clinically distinct disease and is transmitted by a different insect vector.

Q: A patient on steroids presented with nocturnal cough and chronic urticaria. Bronchoalveolar lavage (BAL) staining was done, and the organism shown in the image was identified. What is the most likely organism?

Strongyloides stercoralis. ***Strongyloides stercoralis*** - The image shows a nematode larva in a **bronchoalveolar lavage (BAL) sample**, consistent with **Strongyloides stercoralis**, which is known for its ability to **autoinfect** and cause chronic infections. - The patient's **steroid use** can lead to **Strongyloides hyperinfection syndrome**, explaining the pulmonary symptoms (**nocturnal cough**) due to larval migration into the lungs and the chronic **urticaria** often associated with strongyloidiasis. *Enterobius vermicularis* - This organism primarily causes **pinworm infection**, characterized by **perianal itching** and is typically identified by the **scotch tape test** for eggs, not usually found in BAL or associated with chronic urticaria. - It does not commonly cause significant pulmonary symptoms or hyperinfection syndrome, especially not triggered by steroid use. *Capillaria philippinensis* - This nematode causes **intestinal capillariasis**, characterized by **chronic diarrhea**, **abdominal pain**, and **malabsorption**. - It is not typically associated with pulmonary symptoms like nocturnal cough or chronic urticaria, and is transmitted through fish consumption. *Ancylostoma duodenale* - This is a **hookworm** that causes **iron deficiency anemia**. While it does have a lung migration phase that can cause transient cough, it is not typically associated with chronic urticaria or severe pulmonary disease due to steroid-induced hyperinfection. - The image shows larvae, but the clinical context strongly points to *Strongyloides* due to the steroid use and specific symptoms.

Q: Name the parasite whose microfilariae have a sheath and no nuclei at the tail end.

Wuchereria bancrofti. **Wuchereria bancrofti** - **Wuchereria bancrofti** microfilariae are characterized by the presence of a **sheath** and a **clear tail end** that is devoid of nuclei. - This morphology is a key feature used in the microscopic differentiation of W. bancrofti from other filarial species. *Brugia malayi* - **Brugia malayi** microfilariae also have a **sheath**, but their tail end typically contains **two distinct nuclei** that are spaced apart. - They are generally shorter and have more kinky curves than W. bancrofti. *Loa loa* - **Loa loa** microfilariae possess a **sheath** but are distinguished by their **nuclei extending to the tip** of the tail, often in a more continuous pattern. - They are also known for their diurnal periodicity, which aids in diagnosis. *Onchocerca volvulus* - **Onchocerca volvulus** microfilariae are **unsheathed** and have nuclei that do **not extend to the tail tip**, leaving a distinct clear space. - They are typically found in the skin and subcutaneous tissue, rather than the blood.

Question 1

Which of the following statements is true about hydatid disease?

Accepted Answer

It is a zoonosis

Answer

It is a protozoal disease

Answer

Man is the definitive host

Answer

It is rare in sheep rearing countries

Question 2

A female presents with dysuria and vaginal discharge. Wet mount examination shows pear-shaped organisms. What is the most likely diagnosis?

Accepted Answer

Trichomonas

Answer

Candida

Answer

Chlamydia

Answer

Bacterial vaginosis

Question 3

Which of the following is TRUE about screening for Trichomonas vaginalis?

Accepted Answer

NAAT is recommended for screening high-risk women

Answer

Urine samples are inadequate for testing

Answer

Culture is no longer used for diagnosis

Answer

Wet mount microscopy has sensitivity >95%

Question 4

How does trichomoniasis affect HIV transmission?

Accepted Answer

By increasing HIV viral shedding from genital tract

Answer

By selection for drug-resistant HIV strains

Answer

By direct activation of HIV transcription

Answer

By inhibiting host macrophage function

Question 5

A young boy who used to wash his contact lenses in tap water or with unhygienic lens fluid developed keratitis. Microscopy revealed an organism with spiked or star-shaped structures. Identify the correct organism responsible.

Accepted Answer

Acanthamoeba

Answer

Balantidium

Answer

Pseudomonas

Answer

Staphylococcus aureus

Question 6

A woman presents with a chronic history of fever and lower limb swelling. The microscopic image of a parasite in her blood smear is shown. Identify the pathogen responsible for her condition.

Accepted Answer

Brugia

Answer

Mansonella

Answer

Wuchereria bancrofti

Answer

Loa loa

Question 7

A child presented with perianal itching. The swab specimen is shown in the image. What is the diagnosis?

Accepted Answer

Enterobius

Answer

Ascaris

Answer

Trichiura

Answer

Ancylostoma

Question 8

What is the vector for Leishmania, a parasite characterized by a prominent kinetoplast in its morphological forms?

Accepted Answer

Sand fly

Answer

Female Anopheles Mosquito

Answer

Triatomine bug

Answer

TseTse fly

Question 9

A patient on steroids presented with nocturnal cough and chronic urticaria. Bronchoalveolar lavage (BAL) staining was done, and the organism shown in the image was identified. What is the most likely organism?

Accepted Answer

Strongyloides stercoralis

Answer

Enterobius vermicularis

Answer

Capillaria philippinensis

Answer

Ancylostoma duodenale

Question 10

Name the parasite whose microfilariae have a sheath and no nuclei at the tail end.

Accepted Answer

Wuchereria bancrofti

Answer

Brugia malayi

Answer

Loa loa

Answer

Onchocerca volvulus

Parasitology — MCQs

Parasitology — MCQs

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