Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 1281: Periventricular calcification seen in encephalitis is due to -

A. HSV-I
B. HSV-II
C. CMV (Correct Answer)
D. Herpes Zoster

Explanation: ***CMV*** - **Cytomegalovirus (CMV)** encephalitis, particularly in congenitally infected infants, is classically associated with **periventricular calcifications** due to its destructive effect on neural progenitors around the ventricles. - CMV has an **affinity for immature brain tissue**, leading to inflammation, necrosis, and subsequent calcification in these areas. *HSV-I* - **Herpes Simplex Virus type 1 (HSV-1)** encephalitis typically causes focal lesions, often involving the **temporal and frontal lobes**, and is characterized by neuronal necrosis and hemorrhage, not usually periventricular calcifications. - It does not have the same tropism for the germinal matrix responsible for periventricular calcifications as CMV. *HSV-II* - **Herpes Simplex Virus type 2 (HSV-2)** encephalitis can occur in neonates, usually presenting as a disseminated infection or meningitis/encephalitis. While it can cause significant brain damage, **periventricular calcifications are not its hallmark feature**; hydrocephalus or white matter injury may be seen. - HSV-2 tends to cause a more diffuse inflammatory response rather than the localized damage leading to periventricular calcifications. *Herpes Zoster* - **Varicella-zoster virus (VZV)**, which causes herpes zoster, can lead to encephalitis, particularly in immunocompromised individuals. This often presents as **vasculopathy**, stroke, or focal neurological deficits, typically *without* periventricular calcifications. - VZV encephalitis usually involves inflammation of blood vessels and parenchyma but does not target the periventricular region in a way that causes characteristic calcifications.

Question 1282: In infectious mononucleosis, which cell type shows the most significant pathological changes?

A. B-cells
B. Macrophages
C. NK cells
D. T-cells (Correct Answer)

Explanation: ***Correct: T-cells*** - In response to **Epstein-Barr virus (EBV)** infection of B-cells, there is a massive proliferation of **CD8+ cytotoxic T-lymphocytes** which are responsible for controlling the infection and mediating many of the symptoms. - These activated T-cells, known as **atypical lymphocytes** or **Downey cells**, are the characteristic pathological finding in peripheral blood smears of patients with infectious mononucleosis. - The **lymphocytosis with atypical lymphocytes** (>10% of total WBCs) is the hallmark laboratory finding. *Incorrect: B-cells* - **EBV directly infects B-cells**, leading to their proliferation, but the most significant pathological changes observed in the blood smear are due to the host's immune response. - While B-cells are the primary target of EBV, the hallmark feature of infectious mononucleosis on a peripheral blood smear is the presence of reactive T-cells, not the infected B-cells themselves. *Incorrect: Macrophages* - Macrophages play a role in clearing cellular debris and presenting antigens during an infection, but they do not show the most significant **pathological changes** or proliferative response characteristic of infectious mononucleosis. - They are generally not the predominant cell type exhibiting **atypical morphology** in the peripheral blood during this condition. *Incorrect: NK cells* - **Natural killer (NK) cells** are part of the innate immune response and contribute to controlling viral infections, including EBV. - However, they do not undergo the distinct and extensive **morphological changes** and proliferation seen in T-cells during infectious mononucleosis.

Question 1283: Subacute sclerosing panencephalitis is a late neurological complication associated with infection due to:

A. Rubella virus
B. Parainfluenza virus
C. Mumps virus
D. Measles virus (Correct Answer)

Explanation: ***Measles virus*** - **Subacute sclerosing panencephalitis (SSPE)** is a rare, fatal degenerative disease of the central nervous system caused by a persistent infection of the **measles virus**. - It occurs years after the initial measles infection, typically in children or young adults, due to mutations in the **measles virus (paramyxovirus)** that allow it to remain latent and cause progressive neurological damage. *Rubella virus* - While rubella can cause congenital syndromes, it is not associated with **subacute sclerosing panencephalitis**. - The congenital rubella syndrome can cause neurological damage, but it is a direct consequence of fetal infection, not a delayed degenerative process like SSPE. *Parainfluenza virus* - **Parainfluenza viruses** are primarily respiratory pathogens causing conditions like croup, bronchitis, and pneumonia. - They are not known to cause chronic, delayed neurological complications such as **subacute sclerosing panencephalitis**. *Mumps virus* - Mumps virus can cause **meningitis** or **encephalitis** as acute complications of the infection. - However, it does not typically lead to a delayed, progressive neurodegenerative condition like **subacute sclerosing panencephalitis**.

Question 1284: What is true about gp120?

A. Virus penetration
B. Virus dissemination
C. Virus detachment
D. Virus attachment (Correct Answer)

Explanation: ***Correct: Virus attachment*** - **gp120** is a glycoprotein on the **surface of HIV** that is crucial for binding to **CD4 receptors** on host T-helper cells and macrophages. - This initial binding step is essential for the **HIV life cycle** and marks the beginning of the infection process. - gp120 specifically mediates the **attachment phase** of viral entry, making this the correct answer. *Incorrect: Virus penetration* - Viral penetration, or entry into the cell, occurs **after attachment** and involves the fusion of the viral envelope with the host cell membrane, mediated by the **gp41 protein** (not gp120). - While gp120 initiates the process, it does not directly mediate the fusion and penetration step itself. *Incorrect: Virus dissemination* - Virus dissemination refers to the spreading of the virus throughout the host organism after initial infection and replication. - While gp120's role in initial infection enables subsequent dissemination, dissemination is not the primary function of gp120. *Incorrect: Virus detachment* - Virus detachment typically refers to the release of newly formed viral particles from the host cell. - This process is usually mediated by host cell enzymes or viral enzymes like **neuraminidase** in influenza, not by gp120. - gp120 functions at the **entry stage**, not the exit stage of the viral life cycle.

Question 1285: At present following types of influenza viruses are major circulating strains of clinical significance in the world, except -

A. Type C virus (Correct Answer)
B. H3N2
C. Type B virus
D. H1N1

Explanation: ***Type C virus*** - **Influenza C viruses** cause a **mild respiratory illness** and are not associated with epidemics. - They are generally **not considered a major circulating strain of clinical significance** in annual influenza surveillance or vaccine production. *H3N2* - **Influenza A (H3N2)** is a significant **seasonal influenza A subtype** that frequently undergoes **antigenic drift**, leading to new strains each year. - It is a major component of annual influenza vaccines due to its **clinical impact** and **epidemic potential**. *Type B virus* - **Influenza B viruses** regularly circulate in humans and cause **seasonal epidemics**, often affecting children more severely than Type A. - Two main lineages, **B/Yamagata** and **B/Victoria**, are included in quadrivalent influenza vaccines due to their clinical significance. *H1N1* - **Influenza A (H1N1)**, including the strain that caused the **2009 pandemic**, continues to circulate seasonally. - It is a major **influenza A subtype** responsible for significant morbidity and mortality, and is included in annual influenza vaccines.

Question 1286: In a patient suspected to have Rabies, a corneal smear sample was taken. Which of the following is the MOST SENSITIVE investigation for this specimen?

A. Virus isolation
B. Immunofluorescence test
C. Negri body visualization
D. RT PCR (Correct Answer)

Explanation: ***RT PCR*** - **Reverse transcriptase polymerase chain reaction (RT-PCR)** is the **most sensitive molecular method** for detecting **rabies virus RNA** in corneal smear samples. - It provides **rapid, highly sensitive, and specific** detection of rabies viral nucleic acid, making it the preferred method for antemortem diagnosis from this specimen. - RT-PCR has **higher sensitivity than immunofluorescence** for corneal samples. *Immunofluorescence test* - **Direct fluorescent antibody (DFA) test** can be performed on corneal impression smears and is an established antemortem diagnostic method. - However, its **sensitivity is lower than RT-PCR** for this specific sample type, with higher false-negative rates. - DFA remains the gold standard primarily for **post-mortem brain tissue examination**. *Virus isolation* - Virus isolation is **time-consuming, less sensitive**, and requires specialized biosafety level 3 facilities. - **Corneal smears** have lower viral loads, making isolation less reliable compared to molecular methods. - Not routinely used for rapid diagnosis. *Negri body visualization* - **Negri bodies** are pathognomonic cytoplasmic inclusion bodies found in neurons, particularly in the **hippocampus and cerebellum**. - These can **only be visualized in brain tissue** through histopathological examination (post-mortem). - **Cannot be detected in corneal smears** as they are neuronal inclusions.

Question 1287: Co-infection is essential for disease presentation in:

A. Hepatitis B
B. Hepatitis A
C. Non A Non B Hepatitis
D. Delta Hepatitis (Correct Answer)

Explanation: ***Delta Hepatitis*** - **Delta hepatitis** (Hepatitis D) is a **defective RNA virus** that requires the presence of Hepatitis B surface antigen for replication and expression. - Therefore, infection with **Hepatitis D** can only occur as a co-infection or superinfection with **Hepatitis B virus (HBV)**. *Hepatitis B* - **Hepatitis B virus (HBV)** can cause acute or chronic hepatitis and does not require co-infection with another distinct virus for its disease presentation. - While it can co-infect with Hepatitis D, it is not essential for HBV itself to cause disease. *Hepatitis A* - **Hepatitis A virus (HAV)** is an RNA virus that causes acute hepatitis and is typically transmitted via the fecal-oral route. - It resolves spontaneously in most cases and does not require co-infection with another virus to manifest disease. *Non A Non B Hepatitis* - The term "Non A Non B Hepatitis" was historically used to describe hepatitis cases that were not caused by Hepatitis A or B. - This category was largely replaced by the identification of **Hepatitis C virus (HCV)**, which does not require co-infection with another virus for its disease presentation.

Question 1288: What is the incubation period of Hepatitis B virus?

A. 8-10 days
B. 30-180 days (Correct Answer)
C. 1 year
D. 2 years

Explanation: ***30-180 days*** - The incubation period for **Hepatitis B virus (HBV)** is typically long, ranging from **30 to 180 days**, reflecting the time from exposure to symptom onset or detection of viral markers. - This broad range allows for the virus to replicate and reach a detectable level in the body before clinical signs of **acute hepatitis** manifest. *8-10 days* - An incubation period of **8-10 days** is far too short for Hepatitis B virus. - Such a short period is more characteristic of rapidly acting viral or bacterial infections. *1 year* - A 1-year incubation period is **too long** for typical presentation of acute Hepatitis B. - While chronic infection can persist for years, the initial incubation before symptom onset is much shorter. *2 years* - A 2-year incubation period is also **excessively long** for the acute phase of Hepatitis B infection. - This timeframe is not consistent with the known viral kinetics and immune response associated with HBV.

Question 1289: Juvenile papillomatosis is caused by -

A. HPV (Correct Answer)
B. Adenovirus
C. Parainfluenza virus
D. Influenza virus

Explanation: ***HPV*** - **Juvenile papillomatosis**, often referred to as **recurrent respiratory papillomatosis (RRP)** in children, is primarily caused by **Human Papillomavirus (HPV)**. - Specifically, **HPV types 6 and 11** are responsible for the vast majority of cases, leading to the formation of benign, wart-like growths in the larynx and other parts of the respiratory tract. *Adenovirus* - **Adenovirus** can cause a range of respiratory illnesses, including pharyngitis, bronchitis, and pneumonia. - However, it is not associated with the development of **papillomas** or respiratory papillomatosis. *Parainfluenza virus* - **Parainfluenza viruses** are a common cause of respiratory tract infections, particularly in young children, leading to conditions like **croup**, bronchitis, and bronchiolitis. - They do not cause **papilloma formation** in the respiratory tract. *Influenza virus* - The **influenza virus** is responsible for seasonal epidemics of the flu, characterized by fever, cough, body aches, and respiratory symptoms. - It does not cause the proliferation of **papillomatous growths** in the respiratory system.

Question 1290: True about chicken pox -

A. Rash is deep seated
B. Caused by varicella-zoster virus (Correct Answer)
C. SAR is 70%
D. Scab is infective

Explanation: ***Caused by varicella-zoster virus*** - Chickenpox, also known as varicella, is definitively caused by the **varicella-zoster virus (VZV)**, a member of the herpesvirus family. - VZV is highly contagious and responsible for both primary infection (chickenpox) and latent infection (shingles). *Rash is deep seated* - The rash of chickenpox is characteristically **superficial**, appearing as vesicles on the epidermis and upper dermis, often described as "dewdrops on a rose petal." - Deep-seated lesions are more characteristic of diseases like **smallpox**, which results in deeper scarring. *SAR is 70%* - The **secondary attack rate (SAR)** for chickenpox in susceptible household contacts is much higher than 70%, typically ranging from **80% to 90%**, highlighting its extreme contagiousness. - This high SAR means that most unvaccinated individuals living with an infected person will contract the disease. *Scab is infective* - While scabs contain the virus, the **infectivity significantly decreases** once the lesions have crusted over and formed scabs. - The most infective stages are typically from 1-2 days before the rash appears until all lesions have crusted.

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Virology — MCQs

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