Parasitology Practice Questions

Q: A 65-year old man presented with skin lesions on his chest and left arm and shoulder six weeks after returning from a vacation in Belize at the beach in the rain forest. The lesions occasionally stung, drained a dark exudates, and enlarged despite two weeks of treatment with cephalexin. The patient had no constitutional symptoms. Physical examination revealed five nodules of varying sizes with surrounding erythema and a central pore through which a single, moving larva was observed. The larvae coming out of the pores are-

Dermatobia hominis. ***Dermatobia hominis*** - The description of **cutaneous nodules** with a central pore from which a **moving larva** is observed, particularly after travel to a tropical region like Belize, is classic for **furuncular myiasis** caused by **Dermatobia hominis** larvae (human botfly). - The **"occasional stinging"** and **"dark exudate"** are characteristic symptoms of the larva burrowing in the skin and secreting waste products. *Loa loa* - **Loa loa** (African eye worm) is a filarial nematode that migrates through **subcutaneous tissues** and occasionally across the eye, causing **Calabar swellings**. - It does not present as a **furuncular lesion** with a visible central moving larva emerging from a pore. *Diphyllobothrium latum* - **Diphyllobothrium latum** is a **tapeworm** that infects the intestines and is acquired by consuming undercooked infected fish. - It causes gastrointestinal symptoms and can lead to **vitamin B12 deficiency**, but it does not produce **skin lesions with moving larvae**. *Dracunculus medinensis* - **Dracunculus medinensis** (guinea worm) infection typically results in a **painful blister** on the lower limbs, from which the female worm emerges to release larvae when exposed to water. - While it involves a skin lesion, the presentation of **multiple nodules with a central pore revealing a moving larva** is not consistent with **dracunculiasis**.

Q: Casoni's test is used in the diagnosis of which of the following infections?

Echinococcus granulosus. ***Echinococcus granulosus*** - The **Casoni's test** is an intradermal skin test historically used to detect antigens of **Echinococcus granulosus**, the causative agent of **hydatid disease**. - A **positive reaction** indicates previous exposure to Echinococcus antigens, leading to a local hypersensitivity reaction. *Toxocariasis* - Diagnosis of **toxocariasis** (visceral larva migrans) primarily relies on **serological tests** like ELISA to detect antibodies against *Toxocara* antigens. - While Casoni's test involves an immune reaction, it is not specific or used for **Toxocara** detection. *Toxoplasmosis* - **Toxoplasmosis** is diagnosed through **serological tests** measuring IgG and IgM antibodies to *Toxoplasma gondii*, or by PCR for detecting parasitic DNA. - The Casoni's test has no role in the diagnosis of **Toxoplasma** infection. *Syphilis* - Diagnosis of **syphilis** involves **nontreponemal tests** (e.g., VDRL, RPR) for screening and **treponemal tests** (e.g., TPPA, FTA-ABS) for confirmation. - The Casoni's test is entirely unrelated to the diagnostic methods for **syphilis**.

Q: Which micro–organism is responsible for classical presentation of hydrocephalus, chorioretinitis, intracerebral calcification ?

Toxoplasmosis. ***Toxoplasmosis*** - This classic triad of **hydrocephalus**, **chorioretinitis**, and **intracerebral calcifications** is highly indicative of congenital toxoplasmosis. - *Toxoplasma gondii* is an intracellular parasite acquired transplacentally, leading to these severe neurological and ocular manifestations in the fetus. *CMV* - While congenital CMV can cause **intracerebral calcifications** (often periventricular), it typically presents with **microcephaly** rather than hydrocephalus. - CMV is also commonly associated with **sensorineural hearing loss** and hepatosplenomegaly. *Measles* - Congenital measles is extremely rare and can lead to **miscarriage** or **premature birth**, but not the classic triad described. - Measles is known for causing **subacute sclerosing panencephalitis (SSPE)** much later in life, an entirely different clinical picture. *Rubella* - Congenital rubella syndrome (CRS) is characterized by a different constellation of symptoms, including a **PDA (patent ductus arteriosus)**, **cataracts**, and **sensorineural hearing loss**. - While it can cause some central nervous system abnormalities, it does not typically present with hydrocephalus or chorioretinitis with intracerebral calcifications.

Q: A 24-year-old patient presents with a high-grade fever, headache, and weakness since 5 days. He gives a history of blood transfusion 4 months back. The microscopic examination of the thin blood smear is given below. What is the most probable causative agent?

Babesia microti. ***Babesia microti*** - The image displays **intraerythrocytic pleomorphic ring forms** and classic **tetrad formations (Maltese cross)**, which are pathognomonic for **Babesia microti** infection. - The patient's history of **blood transfusion** 4 months prior is highly suggestive, as babesiosis can be transmitted through contaminated blood products with an incubation period fitting this timeline. - Clinical features include high-grade fever, headache, and weakness, consistent with babesiosis. *Leishmania donovani* - This parasite exists as **amastigotes within macrophages** and does not infect red blood cells or form ring structures as seen in the image. - While it causes fever and weakness (**visceral leishmaniasis/kala-azar**), its microscopic appearance on blood smear shows amastigotes in macrophages, not intraerythrocytic forms. *Plasmodium vivax* - While *P. vivax* infects red blood cells and forms ring stages, it is typically characterized by **enlarged infected RBCs with Schüffner's dots**, which are not seen here. - The **tetrad formations (Maltese cross)** seen in the image are pathognomonic for Babesia, not Plasmodium species. *Plasmodium falciparum* - This parasite typically presents with **multiple small ring forms per RBC** and **applique or "accole" forms** at the periphery of red blood cells. - While *P. falciparum* can cause high fever and severe disease, the specific **tetrad configuration (Maltese cross)** is characteristic of Babesia, not Plasmodium.

Q: Sabin Feldman dye test is used for:

Toxoplasma. ***Toxoplasma*** - The **Sabin-Feldman dye test** is a **serological assay** used to detect specific antibodies against *Toxoplasma gondii*. - This test measures the ability of antibodies in the patient's serum to prevent the cytoplasmic staining of live *Toxoplasma gondii* parasites by a basic dye. *Herpes* - Herpes simplex virus (HSV) infections are typically diagnosed using **viral culture**, **PCR**, or **antigen detection**, not the Sabin-Feldman dye test. - Serological tests for herpes usually involve detecting **IgG or IgM antibodies** to specific HSV glycoproteins. *Syphilis* - Syphilis, caused by *Treponema pallidum*, is diagnosed using **non-treponemal tests** (e.g., RPR, VDRL) and confirmed by **treponemal tests** (e.g., TP-PA, FTA-ABS). - The Sabin-Feldman dye test has no role in the diagnosis of syphilis. *Plasmodium* - *Plasmodium* species are the causative agents of malaria, diagnosed primarily by **microscopic examination of Giemsa-stained blood smears** to identify parasites. - **Rapid Diagnostic Tests (RDTs)** detecting *Plasmodium* antigens are also commonly used.

Q: Infection caused by which of the following organism may mimic as malignancy?

Echinococcus multilocularis. ***Echinococcus multilocularis*** - This parasite causes **alveolar echinococcosis**, which manifests as a **destructive, infiltrative growth** in organs, primarily the liver. [1] - The lesions can be difficult to differentiate from **malignant tumors** due to their invasive nature and irregular margins, often leading to misdiagnosis. [1] *Echinococcus oliganthus* - This species is known to cause **polycystic echinococcosis**, primarily affecting wild felids and occasionally humans through accidental ingestion of eggs. - While it forms cysts, its growth pattern is generally **cystic** rather than infiltrative, making it less likely to mimic malignancy compared to *E. multilocularis*. *Echinococcus vogeli* - This parasite causes **polycystic hydatid disease** (or polycystic echinococcosis), similar to *E. oliganthus*, but is primarily associated with dholes and causes lesions in humans. - The disease typically presents as **large, multiloculated cysts** in organs, which are distinct from the infiltrative, tumor-like lesions of *E. multilocularis*. *Echinococcus granulosus* - This species is responsible for **cystic echinococcosis** (or hydatid disease), forming slow-growing, unilocular cysts, most commonly in the liver and lungs. [1] - While these cysts can grow large, their **well-defined, encapsulated nature** generally makes them distinguishable from malignant tumors, unlike the invasive lesions of alveolar echinococcosis. [1]

Q: An Egyptian fisherman develops lower abdominal pain and pain on urination, and reports seeing blood in his urine. Which of the following parasites is the most likely cause of urinary symptoms in this patient?

Schistosoma haematobium. ***Schistosoma haematobium*** - The patient's presentation with **lower abdominal pain**, **dysuria**, and **hematuria** is highly characteristic of urinary schistosomiasis, caused by *Schistosoma haematobium*. - The patient's origin as an **Egyptian fisherman** places him in an **endemic area** where contact with contaminated fresh water containing the parasite's larval forms (cercariae) is common. *Clonorchis sinensis* - This parasite causes **clonorchiasis**, an infection primarily affecting the **biliary tract** and liver, leading to symptoms like cholangitis, cholecystitis, and hepatomegaly. - It is typically acquired by consuming **raw or undercooked freshwater fish**, but does not cause urinary symptoms. *Fasciola hepatica* - *Fasciola hepatica* causes **fascioliasis**, a **liver fluke infection** that primarily affects the **biliary ducts** leading to symptoms like right upper quadrant pain, fever, and jaundice. - It is acquired by ingesting **metacercariae on aquatic plants**, particularly watercress, and does not cause urinary manifestations. *Diphyllobothrium latum* - This is the **fish tapeworm**, which causes **diphyllobothriasis**, an intestinal infection. - Symptoms are usually mild or asymptomatic, but can include abdominal discomfort, nausea, and notably **vitamin B12 deficiency** leading to megaloblastic anemia, not urinary symptoms.

Q: Which of the following is the most common central nervous system parasitic infestation-

Neurocysticercosis. ***Neurocysticercosis*** - **Neurocysticercosis** is caused by the larval stage of the **pork tapeworm**, *Taenia solium*, and is considered the most common parasitic infection of the central nervous system worldwide [1]. - It is a leading cause of **acquired epilepsy** in endemic areas due to the presence of cysts in the brain tissue. *Sparganosis* - **Sparganosis** is a rare parasitic infection caused by larvae of **Spirometra** tapeworms, typically acquired by ingesting contaminated water or undercooked amphibian/reptile meat. - While it can affect the CNS, it is significantly **less common** than neurocysticercosis. *Paragonimiasis* - **Paragonimiasis** is caused by the lung fluke, mainly *Paragonimus westermani*, and is primarily a **pulmonary infection**. - Although it can rarely lead to **cerebral paragonimiasis**, it is not the most common CNS parasitic infestation. *Echinococcosis* - **Echinococcosis**, or hydatid disease, is caused by tapeworms of the genus *Echinococcus*, leading to the formation of **hydatid cysts** [1]. - While it can affect the brain, causing neurohydatidosis, it is **less frequent** than neurocysticercosis and often presents as a space-occupying lesion.

Q: Painless terminal hematuria is seen as one of the manifestations in the infection caused by ?

Schistosoma haematobium. ***Schistosoma haematobium*** - *Schistosoma haematobium* characteristically infects the **urinary bladder**, leading to inflammation and ulceration of the bladder wall [1]. - This irritation often manifests as **painless terminal hematuria**, which is the passage of blood at the end of micturition without associated pain [1]. *Plasmodium falciparum* - *Plasmodium falciparum* is the causative agent of **malaria**, a parasitic infection that primarily affects red blood cells and the liver. - While it can cause severe systemic symptoms, **hematuria** is not a typical or distinguishing feature of *P. falciparum* infection; rather, it often presents with fever, chills, and organ damage. *Schistosoma japonicum* - *Schistosoma japonicum* primarily infects the **mesenteric veins** of the small intestine, leading to intestinal and hepatic schistosomiasis [1]. - Symptoms are usually gastrointestinal (e.g., abdominal pain, diarrhea) or hepatic (e.g., hepatosplenomegaly), with **urinary tract involvement** and hematuria being highly uncommon [1]. *Schistosoma mansoni* - *Schistosoma mansoni* mainly infects the **mesenteric veins** of the large intestine, causing intestinal schistosomiasis. - Its clinical manifestations typically include **abdominal pain**, bloody diarrhea, and liver fibrosis, but not urinary symptoms like **hematuria**.

Q: Peripheral blood smear in Plasmodium falciparum infection may show all of the following except -

Schizont. ***Schizont*** - While schizonts are a stage in the *Plasmodium falciparum* life cycle, **mature schizonts** (containing merozoites) are typically not seen in peripheral blood smears of infected patients. - They tend to **sequester in deep capillaries** of organs, making their detection in circulating blood extremely rare. *Female gametocyte* - **Crescent-shaped gametocytes** (both male and female) are a characteristic feature of *Plasmodium falciparum* infection that are readily identified in peripheral blood smears. - These forms are responsible for transmission to the mosquito vector. *Trophozoite* - **Ring-form trophozoites** are the most commonly seen stage of *P. falciparum* in peripheral blood smears. - They are typically thin, delicate rings, often with **double chromatin dots** or appliqué forms. *Male gametocyte* - Similar to female gametocytes, **crescent-shaped male gametocytes** are routinely observed in peripheral blood smears of *Plasmodium falciparum* infected individuals. - They are essential for sexual reproduction within the mosquito.

Question 1

A 65-year old man presented with skin lesions on his chest and left arm and shoulder six weeks after returning from a vacation in Belize at the beach in the rain forest. The lesions occasionally stung, drained a dark exudates, and enlarged despite two weeks of treatment with cephalexin. The patient had no constitutional symptoms. Physical examination revealed five nodules of varying sizes with surrounding erythema and a central pore through which a single, moving larva was observed. The larvae coming out of the pores are-

Accepted Answer

Dermatobia hominis

Answer

Loa loa

Answer

Diphyllobothrium latum

Answer

Dracunculus medinensis

Question 2

Casoni's test is used in the diagnosis of which of the following infections?

Accepted Answer

Echinococcus granulosus

Answer

Toxocariasis

Answer

Toxoplasmosis

Answer

Syphilis

Question 3

Which micro–organism is responsible for classical presentation of hydrocephalus, chorioretinitis, intracerebral calcification ?

Accepted Answer

Toxoplasmosis

Answer

CMV

Answer

Measles

Answer

Rubella

Question 4

A 24-year-old patient presents with a high-grade fever, headache, and weakness since 5 days. He gives a history of blood transfusion 4 months back. The microscopic examination of the thin blood smear is given below. What is the most probable causative agent?

Accepted Answer

Babesia microti

Answer

Leishmania donovani

Answer

Plasmodium vivax

Answer

Plasmodium falciparum

Question 5

Sabin Feldman dye test is used for:

Accepted Answer

Toxoplasma

Answer

Herpes

Answer

Syphilis

Answer

Plasmodium

Question 6

Infection caused by which of the following organism may mimic as malignancy?

Accepted Answer

Echinococcus multilocularis

Answer

Echinococcus oliganthus

Answer

Echinococcus vogeli

Answer

Echinococcus granulosus

Question 7

An Egyptian fisherman develops lower abdominal pain and pain on urination, and reports seeing blood in his urine. Which of the following parasites is the most likely cause of urinary symptoms in this patient?

Accepted Answer

Schistosoma haematobium

Answer

Clonorchis sinensis

Answer

Fasciola hepatica

Answer

Diphyllobothrium latum

Question 8

Which of the following is the most common central nervous system parasitic infestation-

Accepted Answer

Neurocysticercosis

Answer

Sparganosis

Answer

Paragonimiasis

Answer

Echinococcosis

Question 9

Painless terminal hematuria is seen as one of the manifestations in the infection caused by ?

Accepted Answer

Schistosoma haematobium

Answer

Plasmodium falciparum

Answer

Schistosoma japonicum

Answer

Schistosoma mansoni

Question 10

Peripheral blood smear in Plasmodium falciparum infection may show all of the following except -

Accepted Answer

Schizont

Answer

Female gametocyte

Answer

Trophozoite

Answer

Male gametocyte

Parasitology — MCQs

Parasitology — MCQs

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