Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 1391: Lysis of a bacterial colony in a culture is caused by which agent?

A. Pox
B. HSV
C. Bacteriophage (Correct Answer)
D. CMV

Explanation: ***Bacteriophage*** - **Bacteriophages** are viruses that infect and **lyse bacteria**, creating clear zones (plaques) on a bacterial lawn. - The lysis of bacterial colonies by bacteriophages is a fundamental observation in **microbiology** used to detect and quantify these viruses. *Pox* - **Poxviruses** infect animal cells, not bacteria, and cause diseases like smallpox or cowpox. - Their replication cycle involves host cell machinery but does not result in the *lysis* of bacterial colonies. *HSV* - **Herpes Simplex Virus (HSV)** is a human virus that causes oral and genital lesions. - HSV infects human cells and does not target or lyse bacterial colonies in culture. *CMV* - **Cytomegalovirus (CMV)** is another human virus, part of the herpesvirus family, causing a wide range of clinical manifestations. - CMV infection is specific to human cells and does not cause lysis of bacterial colonies.

Question 1392: Which virus is primarily associated with Kaposi's sarcoma?

A. Hepatitis C virus (HCV)
B. Human papillomavirus (HPV)
C. Human herpesvirus 8 (HHV-8) (Correct Answer)
D. Herpes simplex virus (HSV)

Explanation: ***Human herpesvirus 8 (HHV-8)*** - **HHV-8**, also known as **Kaposi's sarcoma-associated herpesvirus (KSHV)**, is the causal agent for all forms of Kaposi's sarcoma. - It infects endothelial cells, leading to abnormal proliferation and the characteristic vascular lesions of **Kaposi's sarcoma**, particularly in immunocompromised individuals. *Hepatitis C virus (HCV)* - **HCV** is primarily associated with **hepatocellular carcinoma** and certain **lymphomas**, but not Kaposi's sarcoma. - It causes chronic liver inflammation and can lead to **cirrhosis** and liver failure. *Human papillomavirus (HPV)* - **HPV** is primarily known for causing **cervical cancer**, anogenital warts, and certain **oropharyngeal cancers**. - It does not have a direct causal link to Kaposi's sarcoma. *Herpes simplex virus (HSV)* - **HSV** types 1 and 2 cause **cold sores** (oral herpes) and **genital herpes**, respectively. - While it is a herpesvirus, it is not associated with Kaposi's sarcoma; HHV-8 is a distinct type of herpesvirus.

Question 1393: Among the following viruses, which one does NOT cause hemagglutination?

A. HPV (Correct Answer)
B. Rubella
C. Measles
D. Influenza

Explanation: ***HPV*** - **Human Papillomavirus (HPV)** does not possess **hemagglutinin proteins** on its surface. - Hemagglutination is the process where viruses bind to **red blood cells**, causing them to clump together; HPV does not exhibit this property. *Influenza* - **Influenza viruses** have **hemagglutinin (HA) spikes** on their envelope, which bind to sialic acid residues on red blood cells. - This binding leads to **hemagglutination**, a key property used in diagnostic tests like the hemagglutination inhibition assay. *Rubella* - The **Rubella virus** is known to cause **hemagglutination** of red blood cells, particularly from one-day-old chicks or geese. - This property is utilized in the **hemagglutination inhibition (HI) test** for detecting antibodies against the Rubella virus. *Measles* - **Measles virus**, a paramyxovirus, contains **hemagglutinin proteins** on its surface. - These proteins enable the virus to agglutinate red blood cells, a characteristic contributing to its diagnostic detection.

Question 1394: Which of the following is the envelope glycoprotein of HIV that binds to CD4 receptors for cell entry?

A. Gp73
B. P24
C. GP120 (Correct Answer)
D. Gp5

Explanation: ***GP120*** - **GP120** is the crucial **envelope glycoprotein** found on the surface of the **Human Immunodeficiency Virus (HIV)**. - It is essential for **viral entry** into host cells by binding to the **CD4 receptor** and a **co-receptor (CCR5 or CXCR4)** on T-helper cells. - This makes it a primary target for **neutralizing antibodies** and **vaccine development**. *Gp73* - **Gp73** is a **Golgi protein** that has been studied as a biomarker for **liver fibrosis** and **hepatocellular carcinoma**. - It is **not associated with HIV** structure or function. *P24* - **P24** is a **capsid protein** of HIV that forms the conical core surrounding the viral RNA. - While it is an important **HIV structural protein** used in diagnostic testing, it is **not an envelope glycoprotein**. - P24 is located **inside the virion**, not on the surface, and does not participate in CD4 receptor binding. *Gp5* - **Gp5** refers to a **glycoprotein** associated with other viruses, such as certain **herpesviruses** like **cytomegalovirus (CMV)**. - It is **not a protein of HIV**.

Question 1395: Which of the following statements about the influenza virus is NOT true?

A. Drift is the accumulation of point mutations.
B. Only type A shows antigenic drift.
C. All types exhibit antigenic shift. (Correct Answer)
D. None of the above.

Explanation: ***All types exhibit antigenic shift.*** - This statement is **incorrect** (and thus the correct answer to this question asking for what is NOT true). - **Antigenic shift** is a major genetic reassortment event that occurs primarily in **Influenza A virus**, where entire gene segments are exchanged between different strains, potentially leading to pandemic strains. - **Influenza B** can undergo antigenic drift but does NOT typically exhibit antigenic shift due to its limited host range (primarily humans) and lack of reassortment opportunities. - **Influenza C** causes mild respiratory illness and shows minimal antigenic variation. *Only type A shows antigenic drift.* - This statement is **false**. Both **Influenza A and Influenza B** undergo **antigenic drift**. - Antigenic drift involves gradual accumulation of point mutations in hemagglutinin (HA) and neuraminidase (NA) genes, allowing immune evasion. - This is why this is also an incorrect statement, but the question asks for one answer, and "all types exhibit shift" is the more clearly false statement. *Drift is the accumulation of point mutations.* - This statement is **true**. - **Antigenic drift** results from **point mutations** in genes encoding surface proteins (HA and NA). - These minor changes allow the virus to evade existing immunity, causing seasonal epidemics. *None of the above.* - This option is incorrect because there IS a false statement among the options ("All types exhibit antigenic shift").

Question 1396: H1N1 is a subtype of which virus?

A. SARS virus
B. Influenza type A virus (Correct Answer)
C. Influenza type B virus
D. Influenza type C virus

Explanation: ***Influenza type A virus*** - H1N1 refers to the specific **hemagglutinin (H)** and **neuraminidase (N)** proteins on the surface of the virus, which are characteristic of **influenza A viruses**. - Influenza A viruses are known for their ability to undergo **antigenic shift** and cause pandemics, as seen with the 2009 H1N1 pandemic. *SARS virus* - **SARS (Severe Acute Respiratory Syndrome)** is caused by a coronavirus, specifically **SARS-CoV**, which is distinct from influenza viruses. - While both can cause respiratory illness, their genetic structure and mechanisms of infection are entirely different. *Influenza type B virus* - Influenza B viruses primarily infect humans and do not have the same H and N protein classification (e.g., H1N1) that influenza A viruses do. - They tend to cause **seasonal epidemics** but are not typically associated with pandemics. *Influenza type C virus* - Influenza C viruses cause a **mild respiratory illness** and are not classified by H and N subtypes. - They are less common and cause milder symptoms compared to influenza A and B viruses.

Question 1397: Which paramyxovirus lacks hemagglutinin and neuraminidase but has fusion (F) and attachment (G) proteins?

A. RSV (Correct Answer)
B. CMV
C. HSV
D. Epstein-Barr virus

Explanation: ***RSV*** - **Respiratory Syncytial Virus (RSV)** is unique among paramyxoviruses because it **lacks hemagglutinin and neuraminidase** proteins. - Instead, it primarily relies on its **fusion (F) protein** for cell entry and syncytia formation, and an **attachment (G) protein** for binding to host cells. *CMV* - **Cytomegalovirus (CMV)** is a **herpesvirus**, not a paramyxovirus, and therefore has a different array of envelope glycoproteins (gB, gH, gL, gO) essential for cell entry and immune evasion. - It does not possess hemagglutinin, neuraminidase, or the specific F and G proteins characteristic of paramyxoviruses. *HSV* - **Herpes Simplex Virus (HSV)** is also a **herpesvirus**, distinct from paramyxoviruses in its genomic structure and envelope protein composition. - Its envelope contains various glycoproteins, such as **gB, gC, gD, gE, gH, and gL**, which mediate attachment, entry, and cell-to-cell spread, none of which are hemagglutinin, neuraminidase, or the specific F and G proteins mentioned. *Epstein-Barr virus* - **Epstein-Barr virus (EBV)** is another **herpesvirus**, possessing multiple envelope glycoproteins (e.g., gp350/220, gp42, gH, gL) that facilitate its specific entry mechanisms into B lymphocytes and epithelial cells. - Like other herpesviruses, EBV **lacks hemagglutinin and neuraminidase** and does not encode the F and G proteins seen in paramyxoviruses.

Question 1398: What is the gold standard investigation for Zika virus?

A. Plaque Reduction Neutralization Test (PRNT)
B. IgM Antibody Testing
C. Serological Testing for Zika Virus Antibodies
D. Polymerase Chain Reaction (PCR) (Correct Answer)

Explanation: ***Polymerase Chain Reaction (PCR)*** - **PCR (RT-PCR)** is the gold standard for diagnosing acute Zika virus infection, particularly in the first 7-10 days of illness - It directly detects **viral RNA** in bodily fluids like blood, urine, or cerebrospinal fluid - Provides rapid and specific diagnosis during the viremic phase *Plaque Reduction Neutralization Test (PRNT)* - While PRNT is highly specific, it's primarily used for **confirmatory testing** to differentiate between infections with closely related flaviviruses - It measures **neutralizing antibodies** and requires specialized laboratories with longer turnaround time - Not suitable as a primary diagnostic tool for acute infection *IgM Antibody Testing* - **IgM antibodies** indicate recent infection but have significant **cross-reactivity** with other flaviviruses (dengue, yellow fever) - Less reliable for acute infection as IgM may not be detectable in the very early stages - Requires confirmation with PRNT due to false-positive concerns *Serological Testing for Zika Virus Antibodies* - Broad term including IgM and IgG antibody tests indicating past or recent exposure - Not the gold standard for **acute infection** due to cross-reactivity and time lag for antibody development - Useful for epidemiological studies and confirming past infection

Question 1399: Which of the following statements about Hepatitis C virus characteristics is correct?

A. Easy to culture in standard laboratory conditions
B. Antibody to HCV may not be seen in the acute stage (Correct Answer)
C. Spreads primarily through respiratory droplets
D. Rarely causes chronic hepatitis

Explanation: ***Correct: Antibody to HCV may not be seen in the acute stage*** - It takes time for the body to produce a detectable antibody response after **HCV infection**, leading to a **"window period"** where antibodies are negative but the virus is present - During the **acute phase**, diagnosis relies on detecting **HCV RNA** (viral load) rather than antibodies - **Anti-HCV antibodies** typically appear **6-12 weeks** after infection, making early serological diagnosis unreliable *Incorrect: Easy to culture in standard laboratory conditions* - **HCV** is notoriously **difficult to culture** in vitro, which has historically hindered research and drug development - Its **complex viral replication cycle** and **host-specific factors** make standard laboratory culture challenging - This difficulty delayed HCV research until molecular techniques became available *Incorrect: Spreads primarily through respiratory droplets* - **HCV** is primarily transmitted through **blood-to-blood contact**, such as sharing needles, contaminated medical equipment, or blood transfusions - It does not spread through casual contact, food, water, or **respiratory droplets** - Main routes include **intravenous drug use**, **unsafe medical practices**, and historically **blood transfusions** (before screening) *Incorrect: Rarely causes chronic hepatitis* - A high percentage of individuals infected with **HCV (50-85%)** develop **chronic hepatitis**, which can lead to severe liver disease like **cirrhosis** and **hepatocellular carcinoma** - This high chronicity rate makes HCV a significant public health concern - Unlike Hepatitis A and E, HCV has a **strong tendency toward chronicity**

Question 1400: Which of the following is the causative agent of rubella?

A. Risk of transmission and severity maximum in 1st trimester of pregnancy
B. Rubella vaccine is live attenuated with strain RA 27/3
C. There is no known carrier state for postnatally acquired rubella
D. Caused by RNA virus of Togavirus family (Correct Answer)

Explanation: ***Caused by RNA virus of Togavirus family*** - Rubella, also known as German measles, is caused by a **single-stranded RNA virus** belonging to the **Togaviridae family** (specifically the *Rubivirus* genus). - This classification is important for understanding its replication, transmission, and immune response. *There is no known carrier state for postnatally acquired rubella* - This statement is not the causative agent of rubella; it describes a characteristic of the disease's epidemiology. - While prolonged shedding can occur, a true chronic **carrier state** like that seen in certain other viral infections is not characteristic of rubella. *Rubella vaccine is live attenuated with strain RA 27/3* - This describes the **rubella vaccine**, not the causative agent itself. - The **RA 27/3 strain** refers to the specific attenuated (weakened) virus used in the vaccine to induce active immunity. *Risk of transmission and severity maximum in 1st trimester of pregnancy* - This statement describes a crucial clinical aspect of rubella infection in pregnant women, specifically concerning **congenital rubella syndrome (CRS)**, but it does not identify the causative agent. - The risk of **fetal infection** and severe birth defects is highest when the mother contracts rubella during the **first trimester** of pregnancy.

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Virology — MCQs

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