Parasitology Practice Questions

Q: Definitive host is one in which the parasite lives in which of the following forms?

Adult form. ***Adult form*** - The **definitive host** is defined as the host in which the parasite reaches **sexual maturity** and undergoes **sexual reproduction**. - This typically means the **adult, sexually reproductive stage** of the parasite resides within the definitive host. *Intermediate host* - An **intermediate host** harbors the **larval** or **asexual stages** of a parasite. - It is crucial for the parasite's life cycle but does not involve sexual maturation. *Asexual form* - The **asexual form** of a parasite typically develops within an **intermediate host**. - While essential for multiplication, it does not represent the definitive host stage for sexual reproduction. *Larvae* - **Larvae** are immature forms of parasites that usually reside in an **intermediate host**. - They develop further but do not reach sexual maturity within this host.

Q: A 35 year old man presented with dry cough and rusty colored sputum. He has a history of eating in a Chinese restaurant very often with consumption of crabs. What is the probable causative agent in this condition?

Paragonimus westermani. ***Paragonimus westermani*** - The key clinical features are **dry cough**, **rusty-colored sputum**, and a history of consuming **crabs**. These are classic indicators of **paragonimiasis**. - *Paragonimus westermani* is a **lung fluke** acquired by eating undercooked freshwater crabs or crayfish. *Pneumocystis jirovecii* - This fungus typically causes pneumonia in **immunocompromised individuals**, like those with HIV/AIDS. - While it can cause a dry cough, **rusty-colored sputum** is not a characteristic sign, and there's no mention of immunocompromise. *Strongyloides stercoralis* - This parasite primarily causes **gastrointestinal symptoms** (e.g., abdominal pain, diarrhea) and can lead to cutaneous manifestations (larva currens). - While lung involvement can occur in severe cases (hyperinfection), it does not typically present with **rusty sputum** or a direct association with crab consumption. *Diphyllobothrium latum* - This is the **fish tapeworm**, acquired by eating undercooked freshwater fish. - It primarily causes **gastrointestinal symptoms** such as abdominal pain and diarrhea, and is known for causing **vitamin B12 deficiency** leading to megaloblastic anemia, not pulmonary symptoms.

Q: Flask-shaped ulcers in the intestine are caused by which of the following?

Entamoeba histolytica. ***Entamoeba histolytica*** - *Entamoeba histolytica* is a protozoan that causes **amoebiasis**, which is characterized by **flask-shaped (bottle-shaped) ulcers** in the colon - this is the **pathognomonic feature** of intestinal amoebiasis. - The trophozoites invade the intestinal mucosa and submucosa, creating a **narrow neck at the mucosal surface** and a **wider base in the submucosa**, giving them their unique flask-like appearance. - These ulcers are most commonly found in the **cecum and ascending colon**. *TB* - Intestinal tuberculosis typically causes **transverse ulcers** (perpendicular to the bowel axis) due to lymphatic spread and caseous necrosis, often in the ileocecal region. - These ulcers are usually associated with **granulomas** and acid-fast bacilli, which are histologically distinct from flask-shaped ulcers. *Giardia* - *Giardia lamblia* (or *intestinalis*) is a flagellate that causes **giardiasis**, primarily adhering to the small intestinal villi and causing malabsorption and diarrhea. - It is **non-invasive** and does not penetrate the intestinal wall or cause ulcer formation; its pathology is mainly due to **mucosal inflammation** and villous blunting. *Typhoid* - Typhoid fever, caused by *Salmonella Typhi*, commonly leads to **longitudinal ulcers** (parallel to the bowel axis) in the **Peyer's patches** of the ileum due to bacterial invasion and necrosis of lymphoid tissue. - These ulcers may perforate but do not present with the flask-shaped morphology characteristic of amoebiasis.

Q: Which of the following is the most commonly reported nutritional consequence of heavy Ascaris lumbricoides infection?

Vitamin B12. ***Vitamin B12*** - **Ascaris lumbricoides** infection, particularly heavy infestation, can lead to malabsorption of **Vitamin B12**. [1] - This occurs as the parasites consume the vitamin or interfere with its absorption in the small intestine, potentially leading to **megaloblastic anemia**. [1], [2] *Folic Acid* - While malabsorption can occur in severe parasitic infections, **folic acid deficiency** is less commonly reported as the primary nutritional consequence of Ascaris compared to B12. [2] - Deficiency usually manifests as another form of **megaloblastic anemia**, often seen in conditions like celiac disease or alcoholism. *Vitamin A* - **Vitamin A deficiency** can be exacerbated by chronic infections, including parasitic ones, due to impaired absorption or increased metabolic demand. - However, it's not the most commonly cited specific nutritional consequence of Ascaris infection in many epidemiological studies directly linking the two. *Iron* - **Iron deficiency anemia** is common in many parasitic infections, particularly those causing blood loss like hookworm infections. - While Ascaris can contribute to general poor nutrition, it is not primarily associated with direct iron loss or malabsorption to the same extent as other parasites.

Q: Flask shaped ulcers in colon are caused by:-

Entamoeba histolytica. ***Entamoeba histolytica*** - *Entamoeba histolytica* is a protozoan parasite that invades the **colonic mucosa**, leading to characteristic **flask-shaped ulcers**. - These ulcers are formed as the trophozoites penetrate the epithelium and spread laterally through the submucosa, creating a narrow neck at the mucosal surface and a wider base below. *Giardia lamblia* - *Giardia lamblia* causes **giardiasis**, primarily affecting the **small intestine** and leading to malabsorption and diarrhea. - It typically does not cause invasive disease or ulcer formation in the colon, instead, it attaches to the intestinal villi. *Enterobius vermicularis* - *Enterobius vermicularis* is an intestinal nematode (pinworm) that causes **enterobiasis**, commonly manifesting as **perianal itching**, especially at night. - It is a non-invasive parasite and does not cause ulcers in the colon. *H. Pylori* - *H. pylori* is a bacterium primarily associated with infections of the **stomach** and **duodenum**, causing gastritis, peptic ulcers, and increasing the risk of gastric cancer. - It does not colonize the colon or cause flask-shaped ulcers.

Q: A 35-year-old HIV positive patient comes with intractable diarrhea, crampy abdominal pain and vomiting. Biopsy of small intestine was taken which shows oocysts <10 µm as given below. What is the appropriate diagnosis?

Cryptosporidium parvum. ***Cryptosporidium parvum*** - The classic presentation in an **HIV-positive** patient with **intractable diarrhea**, **abdominal pain**, and identifying **acid-fast oocysts <10 µm** in a small intestine biopsy strongly indicates *Cryptosporidium parvum*. - This parasite is a common cause of **severe diarrheal illness** in immunocompromised individuals. *Giardia lamblia* - While *Giardia lamblia* causes **diarrhea** and **abdominal cramps**, its cysts are larger (10-14 µm) and typically pear-shaped trophozoites are seen, not small acid-fast oocysts. - It usually causes **malabsorption** and **steatorrhea**, and is not typically associated with intractable diarrhea in HIV patients to the same extent as *Cryptosporidium*. *CMV* - **Cytomegalovirus (CMV)** can cause **colitis** or **enteritis** in immunocompromised patients, leading to diarrhea and abdominal pain. - However, diagnosis involves identifying **intranuclear inclusions** (cytomegalic cells) on biopsy, not small cysts or oocysts. *Isospora belli* - *Isospora belli* is another coccidian parasite causing diarrhea in HIV patients, but its oocysts are **larger (20-30 µm)** and **ellipsoidal**, differentiating them from the smaller, round oocysts of *Cryptosporidium*. - Like *Cryptosporidium*, its oocysts are also **acid-fast**, but size and shape are key distinguishing features.

Q: Based on the microscopic image showing a cyst containing 4 nuclei with a smooth refractile wall under stool microscopy examination, identify the parasitic organism:

Giardia lamblia. ***Giardia lamblia*** - The **4 nuclei** with a **smooth refractile wall** in an **oval-shaped cyst** (8-12 µm) is pathognomonic for *Giardia lamblia* cysts. - Key distinguishing features include the **oval shape** and presence of **curved fibrils (median bodies)** without chromatoid bars. *Entamoeba dispar* - Although mature *E. dispar* cysts also contain **4 nuclei**, they are **spherical** (not oval) and measure 10-20 µm in diameter. - *E. dispar* cysts have **peripheral chromatin** arrangement and often contain **chromatoid bars with rounded ends**. *Balantidium coli* - *B. coli* cysts are the **largest parasitic protozoan cysts** (50-70 µm) with a **thick double-layered wall**. - Contains a single **kidney-shaped macronucleus** and small micronucleus, not four nuclei. *Taenia solium* - This **tapeworm** produces **eggs** (30-40 µm) with thick **radially striated embryophore** containing hexacanth embryo. - Does not form cysts with nuclei; instead sheds **eggs or proglottids** in stool samples.

Q: Slow growing alveolar like tumor in liver is caused by:

E. multilocularis. **Correct: E. multilocularis** - *Echinococcus multilocularis* causes **alveolar echinococcosis**, characterized by a slow-growing, infiltrative, and destructive lesion in the liver with a sponge-like, alveolar appearance - This parasite's larval stage forms multiple small cysts that are not encapsulated, leading to a tumor-like mass, often described as having an "alveolar" structure - The growth pattern mimics a malignant tumor, with irregular borders and infiltration into surrounding liver tissue *Incorrect: Amoebic liver abscess* - An amoebic liver abscess is caused by **Entamoeba histolytica** and typically presents as a single or multiple well-defined, encapsulated lesions filled with "anchovy paste-like" pus, which is distinct from an alveolar tumor - These abscesses usually develop relatively quickly (acute to subacute) and are often associated with fever and right upper quadrant pain, unlike the slow, asymptomatic growth of alveolar echinococcosis *Incorrect: E. granulosus* - *Echinococcus granulosus* causes **cystic echinococcosis** (hydatid disease), which typically presents as a single, large, unilocular cyst with a clear, laminated membrane, often surrounded by a fibrous capsule - Unlike *E. multilocularis*, *E. granulosus* cysts tend to be well-defined, spherical, and expansile rather than infiltrative and alveolar - The key distinguishing feature is the **cystic** (unilocular or with daughter cysts) versus **alveolar** (multiple small vesicles) morphology *Incorrect: Cysticercus cellulosae* - *Cysticercus cellulosae* is the larval form of **Taenia solium** and causes cysticercosis, which primarily affects muscles, subcutaneous tissue, brain, and eyes - While it forms cysts, these are typically small, solitary, and calcify in various tissues, not forming a large, infiltrative, alveolar tumor-like mass in the liver - Hepatic cysticercosis is extremely rare

Q: Based on the microscopic image showing an oval cyst containing 4 nuclei with visible fibrils under stool microscopy examination, identify the parasitic organism:

Giardia lamblia. ***Giardia lamblia*** - The presence of a cyst with **4 nuclei** and visible **fibrils** (remnants of flagella) seen on stool microscopy is pathognomonic for *Giardia lamblia*. - *Giardia* cysts are **oval-shaped** and typically contain **two to four nuclei** with characteristic curved fibrils visible within the cyst wall. - The **axostyle** (median body) is a characteristic feature of the **trophozoite** stage, not the cyst stage. *Taenia solium* - *Taenia solium* is a **tapeworm**; its eggs are typically **spherical** with a thick, radially striated embryophore and contain a six-hooked oncosphere, not a multi-nucleated cyst with fibrils. - The larval stage (**cysticercus**) can be found in human tissues, but its cysts do not appear in stool samples in this form. *Entamoeba dispar* - *Entamoeba dispar* cysts typically have **one to four nuclei** but **lack fibrils**; they are morphologically indistinguishable from *Entamoeba histolytica* cysts without molecular methods. - While it can be found in stool, its nuclear and internal structure differs significantly from the described parasitic organism. *Balantidium coli* - *Balantidium coli* cysts are much **larger** than *Giardia* cysts, typically **pear-shaped to ovoid**, and contain a single large **kidney-shaped macronucleus** and a smaller micronucleus. - This parasite is also characterized by the presence of **cilia** on its trophozoite stage.

Q: A known HIV patient on anti-retroviral therapy presented with diarrhea of six months duration. Stool microscopy showed 10-30 micrometer cysts, Kinyoun stain was positive. What is the most likely diagnosis?

Cystoisospora. ***Cystoisospora*** - **Cystoisospora belli** is a common cause of chronic diarrhea in **HIV-infected patients** and presents with oocysts typically measuring **20-30 µm** (the described 10-30 micrometer range encompasses the typical size). - The **Kinyoun acid-fast stain** is characteristically positive for *Cystoisospora* oocysts, which is the key diagnostic feature supporting this diagnosis. - This organism is particularly important in **immunocompromised patients** on ART who present with chronic diarrhea. *Balantidium coli* - **Balantidium coli** is a large ciliate, and its cysts are significantly larger (typically **40-60 µm**) than those described in the patient's stool. - While it can cause diarrhea in immunocompromised individuals, it is **not acid-fast** and therefore would not be positive with the Kinyoun stain. *Cryptosporidium* - **Cryptosporidium** is another common cause of chronic diarrhea in HIV patients, and its oocysts are **acid-fast positive** with the Kinyoun stain. - However, **Cryptosporidium** oocysts are much smaller, typically **4-6 µm**, which is inconsistent with the 10-30 micrometer cysts observed in this case. *Strongyloides* - **Strongyloides stercoralis** is a nematode that can cause chronic diarrhea and hyperinfection in immunocompromised patients, but it primarily produces **larvae** (rhabditiform and filariform) in stool, not cysts. - Its diagnostic forms are **not acid-fast**, and its morphology in stool microscopy is distinctly different from the described cysts.

Question 1

Definitive host is one in which the parasite lives in which of the following forms?

Accepted Answer

Adult form

Answer

Intermediate host

Answer

Asexual form

Answer

Larvae

Question 2

A 35 year old man presented with dry cough and rusty colored sputum. He has a history of eating in a Chinese restaurant very often with consumption of crabs. What is the probable causative agent in this condition?

Accepted Answer

Paragonimus westermani

Answer

Pneumocystis jirovecii

Answer

Strongyloides stercoralis

Answer

Diphyllobothrium latum

Question 3

Flask-shaped ulcers in the intestine are caused by which of the following?

Accepted Answer

Entamoeba histolytica

Answer

TB

Answer

Giardia

Answer

Typhoid

Question 4

Which of the following is the most commonly reported nutritional consequence of heavy Ascaris lumbricoides infection?

Accepted Answer

Vitamin B12

Answer

Folic Acid

Answer

Vitamin A

Answer

Iron

Question 5

Flask shaped ulcers in colon are caused by:-

Accepted Answer

Entamoeba histolytica

Answer

Giardia lamblia

Answer

Enterobius vermicularis

Answer

H. Pylori

Question 6

A 35-year-old HIV positive patient comes with intractable diarrhea, crampy abdominal pain and vomiting. Biopsy of small intestine was taken which shows oocysts <10 µm as given below. What is the appropriate diagnosis?

Accepted Answer

Cryptosporidium parvum

Answer

Giardia lamblia

Answer

CMV

Answer

Isospora belli

Question 7

Based on the microscopic image showing a cyst containing 4 nuclei with a smooth refractile wall under stool microscopy examination, identify the parasitic organism:

Accepted Answer

Giardia lamblia

Answer

Taenia solium

Answer

Balantidium coli

Answer

Entamoeba dispar

Question 8

Slow growing alveolar like tumor in liver is caused by:

Accepted Answer

E. multilocularis

Answer

Amoebic liver abscess

Answer

E. granulosus

Answer

Cysticercus cellulosae

Question 9

Based on the microscopic image showing an oval cyst containing 4 nuclei with visible fibrils under stool microscopy examination, identify the parasitic organism:

Accepted Answer

Giardia lamblia

Answer

Taenia solium

Answer

Balantidium coli

Answer

Entamoeba dispar

Question 10

A known HIV patient on anti-retroviral therapy presented with diarrhea of six months duration. Stool microscopy showed 10-30 micrometer cysts, Kinyoun stain was positive. What is the most likely diagnosis?

Accepted Answer

Cystoisospora

Answer

Balantidium coli

Answer

Cryptosporidium

Answer

Strongyloides

Parasitology — MCQs

Parasitology — MCQs

On this page

Practice by Chapter

Want unlimited practice?