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: Which is true about the inclusion bodies seen in specimen of patient, who underwent a liver transplantation?

Basophilic intranuclear inclusion. ***Basophilic intranuclear inclusion*** - The classic inclusion bodies of **Cytomegalovirus (CMV)**, a common opportunistic infection post-transplant, are **basophilic intranuclear inclusions** often described as "owl's eye" inclusions [1]. - These are found within the nucleus of infected cells, particularly in patients who have undergone **liver transplantation** and are immunosuppressed. *Seen with supravital stain* - **Supravital stains** are used to visualize living cells or structures within them, such as reticulocytes (with new methylene blue) or mitochondria. - CMV inclusion bodies are typically seen on **histopathological examination** of fixed tissue sections stained with H&E, not with supravital stains. *Intracytoplasmic inclusion* - While CMV can also produce **small, eosinophilic intracytoplasmic inclusions** [1], the most characteristic and diagnostic feature is the **large, basophilic intranuclear inclusion**. - Other viruses, like rabies (Negri bodies) or vaccinia, are known for prominent intracytoplasmic inclusions. *Highly sensitive for diagnosis of CMV* - While the presence of these inclusions is **highly specific** for CMV infection, their **sensitivity** can be variable, especially in early or mild infections. - **Molecular methods** like PCR for CMV DNA in blood or tissue are often more sensitive for diagnosis, particularly in the context of transplant patients. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 367-368.

Q: The earliest specific cystoscopic appearance of Bilharzial cystitis is :

Sandy patches. ***Sandy patches*** - **Sandy patches** are the **earliest and most characteristic** specific cystoscopic finding in Bilharzial cystitis (urinary schistosomiasis). [1] - They appear as fine, yellow-golden granules resembling grains of sand, visible through the bladder mucosa, representing **calcified *Schistosoma haematobium* eggs** deposited in the submucosa. - This pathognomonic finding typically appears in the trigone and posterior bladder wall and is the hallmark early sign during cystoscopy. *Pseudo tubercles* - **Pseudo tubercles (bilharzial tubercles)** represent a **later stage** of the disease, occurring after sandy patches. - They are organized granulomatous reactions (granulomas) that form around egg deposits within the bladder wall, appearing as small, whitish-yellow elevated lesions. [1] - While specific for schistosomiasis, they develop after the initial egg deposition phase marked by sandy patches. *Nodules* - **Nodules** represent more advanced inflammatory changes or can be associated with chronic schistosomiasis and potential neoplastic transformation. - They are non-specific and can occur in various bladder pathologies, not characteristic of early disease. *Ulcers* - **Ulcers** develop in advanced stages of Bilharzial cystitis due to chronic inflammation, tissue necrosis, or secondary bacterial infection. - They indicate significant mucosal damage and are not early manifestations of the disease. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 405-406.

Q: What mechanism explains the pathogenesis of Jarisch-Herxheimer reaction in patients treated for syphilis?

Inflammatory response to rapid spirochete lysis. The Jarisch-Herxheimer reaction (JHR) is primarily caused by the rapid destruction of a large number of spirochetes, leading to the release of lipoproteins and other antigenic substances. This release triggers an acute systemic inflammatory response, manifesting as fever, chills, headache, and myalgias. While bacteria do release toxins, Treponema pallidum, the causative agent of syphilis, is a spirochete and does not produce classical endotoxins (which are typically associated with gram-negative bacteria) [1]. The inflammatory mediators are released from the host in response to the rapid breakdown of the spirochetes themselves, not pre-formed endotoxins. JHR is an acute reaction that occurs shortly after the initiation of antibiotic therapy and resolves spontaneously, which is not characteristic of a prolonged autoimmune disease. There is no evidence to suggest that the body produces antibodies against its own tissues as a result of syphilis treatment in JHR. An allergic reaction to penicillin would typically present with hives, pruritus, bronchospasm, or anaphylaxis, and would persist with repeated doses of the drug. The Jarisch-Herxheimer reaction is distinct from an allergic reaction; it is a predictable inflammatory response to spirochete killing and can occur even with non-penicillin therapies for syphilis. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 63-64.

Q: What is the main mechanism by which Treponema pallidum causes tissue damage in tertiary syphilis?

Delayed hypersensitivity reaction. ***Delayed hypersensitivity reaction*** - Tissue damage in **tertiary syphilis**, particularly in the formation of **gummas**, is primarily due to a **Type IV delayed hypersensitivity reaction** to persistent *T. pallidum* antigens. - This immune response leads to chronic inflammation, granuloma formation, and eventual tissue destruction or scarring. *Direct cytotoxic effect* - While *T. pallidum* does elicit an immune response, its primary mechanism of tissue damage in tertiary syphilis is **not direct cytotoxicity** of the spirochetes on host cells. - The organism itself has a relatively **low pathogenic load** in tertiary lesions; the damage is immunologically mediated. *Production of exotoxins* - *T. pallidum* is not known to produce **potent exotoxins** that directly cause the extensive tissue destruction seen in tertiary syphilis. - Its pathogenicity relies on its ability to evade the immune system and induce chronic inflammatory responses. *Endotoxin-mediated inflammation* - *T. pallidum* is a **Gram-negative spirochete**, but the extensive chronic inflammation and tissue damage in tertiary syphilis are not primarily mediated by **endotoxins (lipopolysaccharides)** as seen with some other Gram-negative bacteria. - The characteristic lesions are typically sterile and rich in chronic inflammatory cells, indicative of a persistent immune response rather than acute endotoxic shock.

Q: In lymphoid tissue biopsy from a patient with suspected measles, multinucleated giant cells with 'clockwise' nuclear arrangement are observed. What are these cells called?

Warthin-Finkeldey cells. ***Warthin-Finkeldey cells*** - These are **multinucleated giant cells** with many nuclei arranged in a **\"clockwise\" or syncytial pattern**, a characteristic histopathological finding in **lymphoid tissues (lymph nodes, tonsils, spleen) during prodromal measles**. - They represent a key diagnostic marker for measles infection, formed by the fusion of infected lymphoid cells. - They are typically found **before the appearance of the measles rash**. *Cowdry type A* - **Cowdry type A inclusion bodies** are intranuclear inclusions characteristic of **herpes simplex virus** and **varicella-zoster virus** infections. - They are eosinophilic inclusions surrounded by a clear halo, seen in herpesvirus-infected cells, not measles. *Negri bodies* - **Negri bodies** are eosinophilic, cytoplasmic inclusion bodies found in neurons (especially hippocampal pyramidal cells), characteristic of **rabies infection**. - They are pathognomonic for rabies virus and are not observed in measles. *Henderson-Paterson bodies* - **Henderson-Paterson bodies** are large, eosinophilic intracytoplasmic inclusions (molluscum bodies) found in epidermal cells infected with **molluscum contagiosum virus**. - They are pathognomonic for molluscum contagiosum and have no association with measles.

Q: Which of the following is the most likely cause in a case of granuloma with positive AFB?

Tuberculosis. ***Tuberculosis*** - **Mycobacterium tuberculosis** is the classic cause of **granulomatous inflammation** with **positive AFB** staining in histopathology. - TB is the most common mycobacterial infection worldwide, and **AFB staining** is routinely positive in tissue specimens, making it the standard association for granuloma + AFB. *Leprosy* - While **Mycobacterium leprae** is acid-fast, **AFB positivity** is variable and often requires special techniques for demonstration. - Leprosy is much less common globally, and AFB demonstration in routine histopathology is less reliable compared to tuberculosis. *Syphilis* - Syphilis is caused by **Treponema pallidum**, a **spirochete** that is not acid-fast. - Although syphilis can cause granulomatous inflammation (**gummas**), **AFB staining** would be negative. *Cat scratch disease* - Cat scratch disease is caused by **Bartonella henselae**, a **Gram-negative bacterium**. - While it causes **granulomatous lymphadenitis**, **Bartonella** is not acid-fast, so **AFB** would be negative.

Q: Cellulitis is characterized as:

Nonsuppurative and invasive. ***Nonsuppurative and invasive*** - Cellulitis is considered **nonsuppurative** as it typically lacks macroscopic pus formation, distinguishing it from abscesses. - It is **invasive** because it involves the dermal and subcutaneous tissues, spreading through fascial planes. *Suppurative and invasive* - This description is more indicative of conditions like an **abscess**, which involves localized collections of pus. - While abscesses are invasive, cellulitis characteristically lacks the discrete pus collection. *Nonsuppurative and non-invasive* - Conditions that are nonsuppurative and non-invasive might include self-limiting skin rashes or superficial inflammatory processes. - Cellulitis involves deeper tissue infection, which inherently makes it invasive. *Suppurative and non-invasive* - A condition that is suppurative but non-invasive would be rare and contradictory, as pus formation often indicates a tissue response that is at least locally invasive. - Superficial pustules might be considered suppurative and relatively non-invasive, but cellulitis clearly extends beyond such superficial lesions.

Question 1

Primary complex in which of the following sites suggests congenital tuberculosis?

Accepted Answer

Liver

Answer

Lungs

Answer

Lymph nodes

Answer

Skin

Question 2

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 3

Which is true about the inclusion bodies seen in specimen of patient, who underwent a liver transplantation?

Accepted Answer

Basophilic intranuclear inclusion

Answer

Seen with supravital stain

Answer

Intracytoplasmic inclusion

Answer

Highly sensitive for diagnosis of CMV

Question 4

The earliest specific cystoscopic appearance of Bilharzial cystitis is :

Accepted Answer

Sandy patches

Answer

Pseudo tubercles

Answer

Nodules

Answer

Ulcers

Question 5

What is the primary reason for the development of granuloma formation in tertiary syphilis?

Accepted Answer

Delayed hypersensitivity reaction to treponemal antigens

Answer

Secondary bacterial infection of syphilitic lesions

Answer

Direct tissue invasion by spirochetes

Answer

Vasculitis leading to tissue ischemia

Question 6

What mechanism explains the pathogenesis of Jarisch-Herxheimer reaction in patients treated for syphilis?

Accepted Answer

Inflammatory response to rapid spirochete lysis

Answer

Massive release of treponemal endotoxins

Answer

Autoimmune reaction triggered by treatment

Answer

Allergic reaction to penicillin

Question 7

What is the main mechanism by which Treponema pallidum causes tissue damage in tertiary syphilis?

Accepted Answer

Delayed hypersensitivity reaction

Answer

Direct cytotoxic effect

Answer

Production of exotoxins

Answer

Endotoxin-mediated inflammation

Question 8

In lymphoid tissue biopsy from a patient with suspected measles, multinucleated giant cells with 'clockwise' nuclear arrangement are observed. What are these cells called?

Accepted Answer

Warthin-Finkeldey cells

Answer

Cowdry type A

Answer

Negri bodies

Answer

Henderson-Paterson bodies

Question 9

Which of the following is the most likely cause in a case of granuloma with positive AFB?

Accepted Answer

Tuberculosis

Answer

Syphilis

Answer

Cat scratch disease

Answer

Leprosy

Question 10

Cellulitis is characterized as:

Accepted Answer

Nonsuppurative and invasive

Answer

Suppurative and invasive

Answer

Nonsuppurative and non-invasive

Answer

Suppurative and non-invasive

Infectious Diseases — MCQs

Infectious Diseases — MCQs

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