Infectious Diseases Practice Questions

Q: The given inclusion bodies are characteristic of which of the following organisms? ![img-30.jpeg](img-30.jpeg)

Cytomegalovirus. ***Cytomegalovirus*** - The image displays cells with marked enlargement (**cytomegaly**) and large, basophilic intranuclear inclusion bodies surrounded by a clear halo, which is the classic **"owl's eye"** appearance pathognomonic for Cytomegalovirus (CMV) infection [1]. - These inclusions are composed of viral particles and are typically seen in various tissues, such as the lungs, kidneys, and gastrointestinal tract, especially in **immunocompromised** patients [1]. *Human papillomavirus* - HPV infection is histologically characterized by **koilocytes**, which are squamous epithelial cells with a non-staining perinuclear halo and a wrinkled, hyperchromatic nucleus. - These changes are typically seen in cervical smears (Pap smears) or skin warts and are distinct from the large intranuclear inclusions of CMV. *Epstein-Barr virus* - EBV infection, particularly in infectious mononucleosis, is identified by the presence of **atypical lymphocytes** (Downey cells) in the peripheral blood, which have abundant cytoplasm and indented nuclei. - EBV does not produce the characteristic "owl's eye" intranuclear inclusions seen in the provided image. *Herpes simplex virus* - HSV infection is characterized by **multinucleated giant cells** with molded nuclei and eosinophilic intranuclear inclusions known as **Cowdry type A bodies**. - While both are herpesviruses, the inclusions in HSV typically give a **"ground-glass"** appearance to the nucleus, which is different from the distinct, haloed "owl's eye" inclusion of CMV. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 367-368.

Q: A male patient presents with fever, cough, and hemoptysis. Bronchoalveolar lavage (BAL) fluid examination shows septate hyphae with acute angle (dichotomous) branching under microscopy. What is the most likely diagnosis?

Aspergillosis. ***Aspergillosis*** - The characteristic finding of **septate hyphae** displaying uniform **acute angle (dichotomous) branching** (typically 45°) in the **Bronchoalveolar lavage (BAL)** fluid is the defining microscopic feature of *Aspergillus* infection [1], [2]. - The clinical picture of fever, cough, and **hemoptysis** suggests an invasive pulmonary fungal infection, which *Aspergillus* commonly causes, especially in immunocompromised hosts [1], [2]. *Mucormycosis* - This diagnosis is characterized by **broad, non-septate (aseptate) hyphae** that exhibit irregular branching, typically at a **wide angle (90°)**. - The absence of septae and the differing angle of branching rule out mucormycosis based on the microscopic findings. *Histoplasmosis* - *Histoplasma capsulatum* appears in tissue and BAL primarily as **small, oval, budding yeast forms** (2–4 µm) that are often **intracellular** within macrophages. - It is not a hyphal infection in tissue form and therefore does not show septate hyphae with dichotomous branching. *Candidiasis* - *Candida* is identified by the presence of both **budding yeast cells** and **pseudohyphae** (links of elongated yeast cells) [2]. - Although true septate hyphae can occasionally be seen, it lacks the highly characteristic, uniform **acute-angle dichotomous branching** that is specific to *Aspergillus*. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 396-397. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 318-319.

Q: Identify the Anopheles mosquito larva from the image shown below:

Anopheles. ***Anopheles*** - The first image, showing a larva resting **parallel to the water surface** with a **rudimentary breathing tube**, is characteristic of *Anopheles* mosquito larvae. - Unlike *Culex* or *Aedes* larvae, *Anopheles* lack a prominent siphon, allowing them to lie flat against the water for respiration. *Option B* - This option likely refers to the second or third image, which depicts larvae resting at an angle to the water surface with distinct breathing tubes (siphons). These characteristics are typical of *Culex* or *Aedes* larvae, not *Anopheles*. - The presence of a short or long air tube (siphon) differentiates these from the *Anopheles* larva's rudimentary breathing mechanism. *Option C* - Similar to Option B, this refers to larvae with prominent breathing tubes and an angular resting position. These are features of *Culex* or *Aedes* species. - The specific description of the air tube (short and stout or long and slender with hair tufts) helps further distinguish between *Culex* and *Aedes*, neither of which matches the *Anopheles* morphology shown in the first panel. *Option D* - This option also describes larval types with clear breathing tubes and an angled resting posture, which are not characteristics of *Anopheles* species. - The distinct morphology of the first larva, particularly its parallel resting position and rudimentary breathing tube, is unique to *Anopheles*.

Q: A 23-year-old male presented with abdominal pain and bloody diarrhea of one week duration. The following colonoscopic biopsy is diagnostic of infection with:

Amoebiasis. ***Amoebiasis*** - **Amoebiasis** caused by *Entamoeba histolytica* is characterized by **bloody diarrhea** and **abdominal pain**, which are key clinical features in this case [1] [2]. - Colonoscopic biopsy in amoebiasis often shows **flask-shaped ulcers** and trophozoites of *Entamoeba histolytica* invading the colonic mucosa [1]. *Giardiasis* - **Giardiasis** typically presents with **non-bloody, watery diarrhea**, malabsorption, and flatulence, not bloody diarrhea. - It primarily affects the **small intestine** and is diagnosed by finding cysts or trophozoites in stool, not typically via colonoscopic biopsy for bloody diarrhea. *Enterobius* - **Enterobius vermicularis** (pinworm) infection primarily causes **perianal itching**, especially at night. - It does not typically cause **bloody diarrhea** or significant colonic inflammation visible on colonoscopic biopsy. *Severe bacterial infection* - While severe bacterial infections can cause **bloody diarrhea** (e.g., *Shigella*, *E. coli* O157:H7), the question implies a specific diagnostic finding from the colonoscopic biopsy that points to a parasitic infection. - The term "severe bacterial infection" is broad, and without specific bacterial findings or a characteristic pattern, it is less precise than a specific parasitic diagnosis suggested by the biopsy. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Alimentary System Disease, pp. 364-365. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Gastrointestinal Tract, pp. 801-802.

Question 1

All the following malignancies are associated with HIV, except?

Accepted Answer

Astrocytoma

Answer

Kaposi's Sarcoma

Answer

Non-Hodgkin's lymphoma

Answer

Gastric adenocarcinoma

Question 2

Which of the following is a difference between herpangina and primary herpetic stomatitis?

Accepted Answer

Ulcers are typically seen on the anterior faucial pillars.

Answer

Prodromal symptoms precede the condition.

Answer

The condition is unilateral in nature.

Answer

The condition is viral in etiology.

Question 3

What is the best laboratory test for diagnosing Lupus vulgaris in the oral cavity?

Accepted Answer

Biopsy

Answer

Bacterial smear

Answer

Blood studies

Answer

Blood chemistry

Question 4

What are the clinical features of infectious mononucleosis?

Accepted Answer

All of the above

Answer

Glandular involvement

Answer

Febrile

Answer

Palatine petechiae

Question 5

What is a tuberculoma?

Accepted Answer

A tuberculous periapical granuloma

Answer

A granuloma present in the lungs

Answer

A tuberculous lesion of the lymph nodes

Answer

None of the above

Question 6

A 25-year-old presents with painful vesicular lesions on the lips. A Tzanck smear from the lesion base shows multinucleated giant cells. What is the most likely causative agent?

Accepted Answer

Herpes simplex virus

Answer

Coxsackievirus A16

Answer

Human papillomavirus

Answer

Varicella-zoster virus

Question 7

The given inclusion bodies are characteristic of which of the following organisms? ![img-30.jpeg](img-30.jpeg)

Accepted Answer

Cytomegalovirus

Answer

Epstein-Barr virus

Answer

Herpes simplex virus

Answer

Human papillomavirus

Question 8

A male patient presents with fever, cough, and hemoptysis. Bronchoalveolar lavage (BAL) fluid examination shows septate hyphae with acute angle (dichotomous) branching under microscopy. What is the most likely diagnosis?

Accepted Answer

Aspergillosis

Answer

Mucormycosis

Answer

Histoplasmosis

Answer

Candidiasis

Question 9

Identify the Anopheles mosquito larva from the image shown below:

Accepted Answer

Anopheles

Answer

Larva with long slender air tube at angle to water surface

Answer

Larva with prominent siphon and hair tufts

Answer

Larva with short stout air tube at angle to water surface

Question 10

A 23-year-old male presented with abdominal pain and bloody diarrhea of one week duration. The following colonoscopic biopsy is diagnostic of infection with:

Accepted Answer

Amoebiasis

Answer

Giardiasis

Answer

Enterobius

Answer

Severe bacterial infection

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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