Parasitology Practice Questions

Q: Identify the microorganism shown in the image.

Entamoeba histolytica. ***Entamoeba histolytica*** - The image displays the **trophozoite** stage, characterized by a single nucleus with a central, dot-like **karyosome**. - A key diagnostic feature seen here is the presence of ingested **red blood cells** within the cytoplasm, a phenomenon known as **erythrophagocytosis**, which indicates invasive disease. *Giardia lamblia* - *Giardia* trophozoites are pear-shaped and **binucleated**, often described as having a face-like appearance, which is distinct from the single nucleus seen in the image. - They are flagellated protozoa and do not phagocytose red blood cells. *Shigella dysenteriae* - *Shigella* is a **bacterium**, not a protozoan, and would appear as a small, rod-shaped organism under a microscope. - It lacks the complex eukaryotic structures, such as a distinct nucleus and cytoplasmic inclusions, that are visible in the provided image. *Campylobacter jejuni* - This is a **bacterium** known for its characteristic curved, S-shaped, or "gull-wing" morphology. - As a prokaryote, it is much smaller and structurally simpler than the large amoeboid parasite shown.

Q: A girl, after returning from a picnic, complains of pain in her eyes. She had not maintained proper hygiene of her contact lenses. What would be the cause?

Acanthamoeba. ***Acanthamoeba*** - **Acanthamoeba** is a free-living amoeba commonly found in water sources (tap water, lakes, swimming pools) and soil. - Poor contact lens hygiene, such as rinsing lenses or storing them in non-sterile solutions (like tap water, which might be encountered during a picnic or travel hygiene lapse), is a key risk factor for **Acanthamoeba keratitis (AK)**. - AK is characterized by severe ocular pain, often disproportionate to the clinical findings, and can lead to a pathognomonic **ring-shaped corneal infiltrate**. - The combination of **outdoor water exposure + contact lens use + poor hygiene** strongly suggests Acanthamoeba. *Pseudomonas aeruginosa* - **Pseudomonas aeruginosa** is the most common cause of **bacterial keratitis** in contact lens users, especially with improper hygiene. - It typically causes rapidly progressive, purulent corneal ulceration with a characteristic greenish discharge. - While very common in contact lens wearers, the clinical picture here (picnic setting with potential water exposure) more specifically points to a protozoal etiology. *Herpes simplex virus* - **Herpes simplex virus (HSV)** causes recurrent viral keratitis, typically presenting with characteristic **dendritic ulcers** on the cornea. - HSV transmission is via contact with infected bodily fluids or reactivation of latent virus, not through contact lens solution contamination. *Fusarium* - **Fusarium** is a fungus that can cause fungal keratitis in contact lens wearers, particularly with exposure to organic matter or contaminated lens solutions. - Fungal keratitis tends to have a more indolent course with feathery, elevated stromal infiltrates. - While possible in contact lens users, the specific epidemiological context and clinical pattern here favor Acanthamoeba over Fusarium.

Q: A HIV-positive patient presents with chronic diarrhoea for 4 weeks. Stool microscopy shows oval/ elliptical cysts measuring 16 X 20 μm. Diagnosis is?

Cystoisospora. ***Cystoisospora*** - The finding of large, oval/ellipsoidal oocysts (typically **20-33 μm** long, range includes the 16 x 20 μm given) in the stool of an HIV patient with chronic diarrhea is diagnostic of **Cystoisospora belli** infection. - *Cystoisospora* causes chronic, profuse watery diarrhea in immunocompromised hosts (like those with **AIDS**) and is effectively treated with **trimethoprim-sulfamethoxazole (TMP-SMX)**. *Cryptosporidium* - This parasite is characterized by small, **spherical oocysts** measuring only **4–6 μm** in diameter, which is much smaller than the size reported (16 x 20 μm). - While *Cryptosporidium* is a common cause of chronic diarrhea in AIDS, the oocyst morphology does not match the description. *Cryptococcus* - **Cryptococcus** is a fungal pathogen (*C. neoformans*) primarily known for causing **meningoencephalitis** in HIV patients, not typically large oval/elliptical oocysts in stool causing chronic primary diarrhea. - Diagnosis relies on visualization of encapsulated yeast in CSF (e.g., **India ink stain**) or **cryptococcal antigen (CrAg)** testing. *Cyclospora* - *Cyclospora cayetanensis* oocysts are medium-sized and **spherical**, typically measuring **8–10 μm** in diameter. - Although it causes prolonged diarrhea in immunocompromised individuals, the oocyst shape (**oval/elliptical**) and size (16 x 20 μm) clearly distinguish it from *Cyclospora*.

Q: A 25-year-old female presents with complaints of a yellowish-green, foul-smelling vaginal discharge. She reports painful urination and pain during intercourse & no itching. On speculum examination, her vulva and vaginal walls appear inflamed. What is the causative agent?

Trichomonas vaginalis. ***Trichomonas vaginalis***- The classic clinical presentation of **trichomoniasis** includes a copious, frothy (though not always), **yellowish-green**, and distinctly **foul-smelling** vaginal discharge.- The organism causes inflammation and tissue damage (vaginitis/vulvitis), leading to common symptoms like **dysuria** and **dyspareunia**, often without significant pruritus (itching). *Candida albicans*- This fungal infection typically causes a thick, **white, 'cottage cheese-like'** vaginal discharge.- The hallmark symptom is intense **vulvovaginal pruritus** (itching), which is explicitly reported as absent in this patient. *Gardnerella vaginalis*- This bacterium is the most common cause of **Bacterial Vaginosis (BV)**, which produces a thin, **grayish-white** discharge with a characteristic **fishy odor**.- BV often causes minimal inflammation (no significant vulvitis) and typically does not present with the bright yellowish-green discharge described. *Neisseria gonorrhoeae*- While *N. gonorrhoeae* can cause **cervicitis** and **urethritis** (leading to dysuria), the discharge is usually described as **mucopurulent** rather than copious, foul-smelling, and yellowish-green.- The overall clinical picture (discharge color, odor, and inflammation) points more specifically toward a **prototozoal vaginitis**.

Q: A baby is born with microcephaly, intracerebral calcification and chorioretinitis. Which teratogenic infection is the mother suffering from?

Toxoplasma. ***Toxoplasma*** - The triad of **microcephaly**, diffuse **intracerebral calcifications**, and **chorioretinitis** is pathognomonic for symptomatic congenital **Toxoplasmosis**. - This parasitic infection, caused by *Toxoplasma gondii*, is often acquired by the mother through exposure to **cat feces** or ingestion of **undercooked meat** during pregnancy. *CMV* - While CMV causes microcephaly and calcifications (part of the TORCH complex), its calcifications are typically located **periventricularly** rather than diffusely throughout the cortex. - CMV is the leading infectious cause of **sensorineural hearing loss** in children, a major feature often emphasized in its presentation. *Varicella* - Congenital varicella syndrome typically involves specific cutaneous findings, such as **zig-zag skin scarring**, along with **limb hypoplasia**. - Ocular findings in varicella are usually limited to **microphthalmia** and cataracts, not the characteristic chorioretinitis seen here. *Rubella* - Congenital rubella syndrome is defined by defects like **sensorineural hearing loss**, ocular abnormalities (e.g., **cataracts**), and congenital heart defects (**patent ductus arteriosus**). - Although it causes microcephaly, it usually does **not** cause prominent diffuse intracerebral calcifications or chorioretinitis as the primary ophthalmic lesion.

Q: Which among the following parasites directly invade the skin?

Schistosoma mansoni. ***Schistosoma mansoni***- The infectious stage, the **cercariae**, actively penetrate the intact skin of the human host when swimming or wading in contaminated water. - This stage bypasses the need for an insect vector and directly initiates infection, often causing **'swimmer's itch'** at the site of entry.*Dracunculus medinensis*- This infection is acquired by the oral route through ingestion of **copepods** (water fleas) containing the larval stage in drinking water.- While the mature female worm creates a painful **blister** to exit the skin, it does not invade the skin to initiate the infection.*Wuchereria bancrofti*- This parasite is transmitted by the bite of an **infected mosquito** (e.g., *Culex*), which deposits infective larvae near the bite site.- The larvae enter the host through the **puncture wound** created by the mosquito bite, not by actively penetrating intact dermal layers.*Onchocerca volvulus*- The transmission involves the bite of an infected **blackfly** (*Simulium* species), which transmits the infective larvae (microfilariae) into the host.- The larvae enter through the **wound site** created by the fly bite and subsequent manipulation of the wound by the vector (not direct skin invasion).

Q: Choose the organisms that have two morphological forms: 1. Acanthamoeba 2. Naegleria 3. Giardia 4. Trichomonas

1, 3 are correct. ***1, 3 are correct*** - **Acanthamoeba** has exactly **two morphological forms**: the **trophozoite** (active, feeding form) and the **cyst** (dormant, resistant form). The cyst form allows survival in adverse environmental conditions. - **Giardia lamblia** also has exactly **two forms**: the **trophozoite** (flagellated, binucleate form that colonizes the small intestine) and the **cyst** (quadrinucleate, infectious form passed in feces). - Both organisms strictly exhibit a **two-stage life cycle** with trophozoite and cyst stages only. *Incorrect: 1, 2 are correct* - While **Acanthamoeba** does have two forms, **Naegleria fowleri** has **THREE morphological forms**: amoeboid trophozoite, temporary flagellate form, and cyst. - The flagellate form of Naegleria is a distinctive third morphological stage that appears under certain environmental conditions (e.g., distilled water). - Therefore, Naegleria does **not** meet the criteria of having exactly two forms. *Incorrect: 1, 2, 3, 4 are correct* - **Trichomonas vaginalis** exists **only as a trophozoite** and has **no cyst stage**, making it a single-form organism. - The absence of a cyst form in Trichomonas explains why it requires direct transmission (sexual contact) and cannot survive long outside the host. - This option incorrectly includes both Naegleria (three forms) and Trichomonas (one form). *Incorrect: 1, 4 are correct* - **Trichomonas vaginalis** lacks a cyst stage entirely, existing only as a motile trophozoite with four anterior flagella and an undulating membrane. - This makes Trichomonas unsuitable for the answer as it does not have two morphological forms.

Q: A child presents with anal pruritus. Microscopy of the stool sample reveals a plano-convex egg. Identify the pathogen.

Enterobius. ***Enterobius*** - **_Enterobius vermicularis_** (pinworm) is the classic cause of **perianal pruritus** (anal itching), especially at night, which is a hallmark symptom in children. - The eggs are characteristically **plano-convex** (flattened on one side) or D-shaped, matching the description in the question. Diagnosis is typically confirmed with the **Graham sticky tape test**. ***Trichuris*** - The eggs of **_Trichuris trichiura_** (whipworm) are **barrel-shaped** with prominent **polar plugs** at each end, which does not match the description. - Heavy infections can lead to **rectal prolapse**, abdominal pain, and dysentery, but not typically isolated anal pruritus. ***Ascaris*** - **_Ascaris lumbricoides_** eggs are either corticated (with a bumpy, mamillated outer layer) or decorticated (smooth), but they are round-to-oval, not plano-convex. - Clinical features include **pneumonitis** during larval migration (**Loeffler's syndrome**) and potential **intestinal or biliary obstruction** in heavy infections. ***Ancylostoma*** - The eggs of **_Ancylostoma duodenale_** (hookworm) are oval with a thin, smooth shell, containing a developing embryo (blastomeres), which is morphologically distinct. - Hookworm infection is a major cause of **iron deficiency anemia** due to chronic blood loss from the intestine.

Q: Which of the following parasites is capable of causing autoinfection leading to hyperinfection syndrome?

Strongyloides stercoralis. ***Strongyloides stercoralis*** - This parasite is unique among helminths for its ability to cause **autoinfection with hyperinfection syndrome**, a potentially life-threatening condition. - The **rhabditiform larvae** can accelerate development directly into invasive **filariform larvae** within the host's large intestine. - This transformation allows the infectious filariform larvae to penetrate the intestinal mucosa or perianal skin, leading to persistent infection and potentially fatal **hyperinfection syndrome** in immunocompromised hosts. - This makes *S. stercoralis* the most clinically significant parasite causing autoinfection. *Incorrect: Ancylostoma duodenale* - This hookworm does not cause autoinfection, as its eggs must exit the host and mature in the soil to form infectious **filariform larvae**. - Infection occurs through **percutaneous penetration** (skin penetration) by larvae from the external environment. *Incorrect: Ascaris lumbricoides* - This large roundworm requires an environmental phase where unembryonated eggs mature in the soil before becoming infectious upon ingestion (**fecal-oral route**). - Its life cycle involves migration through the lungs (pulmonary phase), but it lacks the mechanism for internal autoinfection. *Incorrect: Hymenolepis nana* - *H. nana* (dwarf tapeworm) is capable of internal autoinfection where eggs hatch within the intestinal lumen and **oncospheres** invade the villi directly. - However, it does **not** cause hyperinfection syndrome like *S. stercoralis*, making it clinically less significant in this context. - The question specifically asks about autoinfection leading to hyperinfection syndrome, which is unique to *Strongyloides stercoralis*.

Question 1

A 20-year-old female presents with hepatosplenomegaly, fever, pallor, and generalized lymphadenopathy. Which laboratory tests are useful for diagnosis?

Accepted Answer

ESR, Electrophoresis, ELISA

Answer

ESR, Electrophoresis, Parasite detection

Answer

Parasite detection, ELISA, Routine haemogram

Answer

ESR, Parasite detection, ELISA

Question 2

Identify the microorganism shown in the image.

Accepted Answer

Entamoeba histolytica

Answer

Giardia lamblia

Answer

Campylobacter jejuni

Answer

Shigella dysenteriae

Question 3

A girl, after returning from a picnic, complains of pain in her eyes. She had not maintained proper hygiene of her contact lenses. What would be the cause?

Accepted Answer

Acanthamoeba

Answer

Pseudomonas aeruginosa

Answer

Herpes simplex virus

Answer

Fusarium

Question 4

A HIV-positive patient presents with chronic diarrhoea for 4 weeks. Stool microscopy shows oval/ elliptical cysts measuring 16 X 20 μm. Diagnosis is?

Accepted Answer

Cystoisospora

Answer

Cryptosporidium

Answer

Cyclospora

Answer

Cryptococcus

Question 5

A 25-year-old female presents with complaints of a yellowish-green, foul-smelling vaginal discharge. She reports painful urination and pain during intercourse & no itching. On speculum examination, her vulva and vaginal walls appear inflamed. What is the causative agent?

Accepted Answer

Trichomonas vaginalis

Answer

Candida albicans

Answer

Neisseria gonorrhoeae

Answer

Gardnerella vaginalis

Question 6

A baby is born with microcephaly, intracerebral calcification and chorioretinitis. Which teratogenic infection is the mother suffering from?

Accepted Answer

Toxoplasma

Answer

CMV

Answer

Varicella

Answer

Rubella

Question 7

Which among the following parasites directly invade the skin?

Accepted Answer

Schistosoma mansoni

Answer

Wuchereria bancrofti

Answer

Onchocerca volvulus

Answer

Dracunculus medinensis

Question 8

Choose the organisms that have two morphological forms: 1. Acanthamoeba 2. Naegleria 3. Giardia 4. Trichomonas

Accepted Answer

1, 3 are correct

Answer

1, 2, 3, 4 are correct

Answer

1, 4 are correct

Answer

1, 2 are correct

Question 9

A child presents with anal pruritus. Microscopy of the stool sample reveals a plano-convex egg. Identify the pathogen.

Accepted Answer

Enterobius

Answer

Ascaris

Answer

Trichuris

Answer

Ancylostoma

Question 10

Which of the following parasites is capable of causing autoinfection leading to hyperinfection syndrome?

Accepted Answer

Strongyloides stercoralis

Answer

Ascaris lumbricoides

Answer

Ancylostoma duodenale

Answer

Hymenolepis nana

Parasitology — MCQs

Parasitology — MCQs

On this page

Practice by Chapter

Want unlimited practice?