Virology — MCQs
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Which of the following sexually transmitted infections is caused by a retrovirus?
What is the cause of Herpes Zoster?
Which virus is known to cause latent infections?
Which of the following is an oncogenic DNA virus primarily associated with lymphoproliferative disorders?
Which virus has a double-stranded RNA with a segmented genome?
Virus causing oropharyngeal carcinoma?
Molluscum contagiosum virus belongs to?
DNA polymerase of HBV is encoded by which of the following ?
What is the window period in HIV infection?
Among the following, which is the smallest virus?
Virology Indian Medical PG Practice Questions and MCQs
Question 1321: Which of the following sexually transmitted infections is caused by a retrovirus?
- A. Human Immunodeficiency Virus (HIV) (Correct Answer)
- B. Hepatitis B Virus (HBV)
- C. Human Papillomavirus (HPV)
- D. Herpes Simplex Virus (HSV)
Explanation: ***Human Immunodeficiency Virus (HIV)*** - HIV is a **retrovirus** characterized by its use of the enzyme **reverse transcriptase** to convert its RNA genome into DNA. - This viral DNA then integrates into the host cell's genome, leading to a persistent infection and eventual immune system compromise. *Human Papillomavirus (HPV)* - HPV is a **DNA virus** responsible for causing warts and is associated with various cancers, particularly cervical cancer. - It replicates within the nucleus of host cells without utilizing reverse transcriptase. *Hepatitis B Virus (HBV)* - While HBV has a complex replication cycle involving reverse transcription, it is classified as a **hepadnavirus**, not a retrovirus. - Its genome is partially double-stranded DNA, and reverse transcription is used to produce DNA from an RNA intermediate during replication. *Herpes Simplex Virus (HSV)* - HSV is a **DNA virus** belonging to the Herpesviridae family, known for causing oral and genital lesions. - It replicates its DNA genome directly within the host cell nucleus and does not involve reverse transcriptase.
Question 1322: What is the cause of Herpes Zoster?
- A. Primary infection with VZV
- B. Recurrent infection with VZV
- C. Reactivation of latent infection of VZV (Correct Answer)
- D. Multiple infection with VZV
Explanation: ***Reactivation of latent infection of VZV*** - Herpes Zoster, commonly known as **shingles**, occurs when the **varicella-zoster virus (VZV)**, which lies dormant in sensory ganglia after a primary chickenpox infection, reactivates. - This **reactivation** typically happens due to a decline in cellular immunity, often associated with age, stress, or immunosuppression. *Primary infection with VZV* - A primary infection with VZV causes **chickenpox** (varicella), not herpes zoster. - After chickenpox resolves, the virus establishes a **latent infection** in the dorsal root ganglia. *Recurrent infection with VZV* - While VZV can cause recurrent episodes, the term "recurrent infection" usually implies a new exposure or reinfection, which is not the typical mechanism for shingles. - Shingles is specifically due to the **awakening of the existing latent virus**, not a new external infection. *Multiple infection with VZV* - "Multiple infection" implies several separate instances of exposure and infection, which is not the underlying cause of Herpes Zoster. - Herpes Zoster arises from the **viral genome already present** within the host's nerve cells.
Question 1323: Which virus is known to cause latent infections?
- A. Rubella
- B. HBV (Correct Answer)
- C. Influenza virus
- D. Rotavirus
Explanation: ***HBV*** - Among the options listed, **Hepatitis B virus (HBV)** is the best answer, though it's important to note that HBV causes **chronic infection** rather than true **latent infection**. - In chronic HBV infection, the virus persists in hepatocytes with ongoing low-level replication for years to decades, and viral DNA can integrate into the host genome. - **True latent infections** are classically caused by **herpesviruses** (HSV, VZV, EBV, CMV), where viral genomes remain dormant in neurons or lymphocytes with NO active replication until reactivation. - HBV's persistence and potential for reactivation (especially with immunosuppression) makes it the most appropriate choice among these options. *Rubella* - Rubella virus causes a **self-limiting acute infection** that resolves completely within weeks. - After clearance, individuals develop **lifelong immunity** through antibodies, but the virus does not persist in the body. - No latent or chronic infection occurs. *Influenza virus* - Influenza viruses cause **acute respiratory infections** that resolve within 1-2 weeks. - The virus is completely **cleared from the body** after the immune response. - No latency or chronicity is established. *Rotavirus* - Rotavirus causes **acute gastroenteritis** lasting 3-8 days. - The virus is eliminated from the body after the acute illness resolves. - Does not establish persistent, chronic, or latent infections.
Question 1324: Which of the following is an oncogenic DNA virus primarily associated with lymphoproliferative disorders?
- A. HTLV
- B. Epstein-Barr Virus (EBV) (Correct Answer)
- C. Human Immunodeficiency Virus (HIV)
- D. HBV
Explanation: ***Epstein-Barr Virus (EBV)*** - **EBV** is a DNA virus strongly associated with several **lymphoproliferative disorders**, including **Burkitt lymphoma**, **Hodgkin lymphoma**, and **post-transplant lymphoproliferative disorder (PTLD)**. - It infects **B lymphocytes** and promotes their proliferation, leading to the risk of malignant transformation. *Human Immunodeficiency Virus (HIV)* - **HIV** is an **RNA retrovirus** that causes acquired immunodeficiency syndrome (AIDS), which can lead to an increased risk of various cancers, including lymphomas, but it is not a DNA virus and its primary mechanism of oncogenesis is indirect via immunosuppression. - While HIV is often associated with lymphomas, it does not directly cause lymphoproliferation in the same way **EBV** does; instead, it weakens the immune system, allowing other oncogenic viruses like EBV to cause malignancies. *HTLV* - **Human T-lymphotropic virus (HTLV)** is an **RNA retrovirus** specifically associated with **adult T-cell leukemia/lymphoma**, not primarily B-cell lymphoproliferative disorders. - It is an **RNA virus**, not a DNA virus, and its oncogenic mechanism involves persistent T-cell activation and proliferation. *HBV* - **Hepatitis B virus (HBV)** is a **DNA virus** primarily associated with **hepatocellular carcinoma (HCC)**, a liver cancer. - It is not directly linked to **lymphoproliferative disorders** but rather to chronic liver inflammation and fibrosis, which contributes to liver cancer.
Question 1325: Which virus has a double-stranded RNA with a segmented genome?
- A. Influenza
- B. Arenavirus
- C. Bunyavirus
- D. Rotavirus (Correct Answer)
Explanation: ***Rotavirus*** - Rotavirus possesses a **double-stranded RNA (dsRNA) genome** that is **segmented** into **11 segments**. - This unique genomic structure is characteristic of the *Reoviridae* family, to which Rotavirus belongs. *Influenza* - Influenza virus has a **segmented single-stranded RNA (ssRNA) genome** of negative sense, not double-stranded RNA. - It belongs to the *Orthomyxoviridae* family. *Arenavirus* - Arenaviruses have a **segmented single-stranded RNA (ssRNA) genome** with an **ambisense** polarity, not double-stranded. - Their genome typically consists of two segments. *Bunyavirus* - Bunyaviruses contain a **segmented single-stranded RNA (ssRNA) genome** of negative or ambisense polarity, not double-stranded. - Their genome is typically divided into three segments.
Question 1326: Virus causing oropharyngeal carcinoma?
- A. Human T-lymphotropic virus (HTLV)
- B. Epstein-Barr Virus (EBV)
- C. Human Herpesvirus 8 (HHV-8)
- D. Human Papillomavirus (HPV) (Correct Answer)
Explanation: ***Human Papillomavirus (HPV)*** - **HPV** is a well-established cause of **oropharyngeal carcinoma**, particularly HPV type 16. - The virus integrates its DNA into host cells, leading to overexpression of **oncoproteins E6 and E7**, which inactivate tumor suppressor genes like p53 and Rb. *Epstein-Barr Virus (EBV), which is linked to certain head and neck cancers.* - **EBV** is associated with **Nasopharyngeal Carcinoma (NPC)**, not typically oropharyngeal carcinoma. - While both are in the head and neck region, NPC has distinct epidemiology and genetic associations compared to oropharyngeal cancers linked to HPV. *Human T-lymphotropic virus (HTLV), a virus with potential oncogenic properties.* - **HTLV-1** is primarily associated with **Adult T-cell Leukemia/Lymphoma** and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). - It does not have a recognized role in the causation of oropharyngeal carcinoma. *Human Herpesvirus 8 (HHV-8), implicated in some malignancies.* - **HHV-8** is most famously known as the causative agent of **Kaposi's sarcoma**, primarily affecting immunocompromised individuals. - It is also linked to certain lymphoproliferative disorders but not oropharyngeal carcinoma.
Question 1327: Molluscum contagiosum virus belongs to?
- A. Poxviruses (Correct Answer)
- B. Herpesviruses
- C. Picornaviruses
- D. Adenovirus
Explanation: ***Poxviruses*** - Molluscum contagiosum virus (MCV) is a **DNA virus** belonging to the **Poxviridae family**, genus Molluscipoxvirus. - Poxviruses are among the **largest and most complex viruses**, with a characteristic **brick-shaped or ovoid morphology**. - MCV causes **cutaneous lesions** characterized by smooth, pearly, dome-shaped papules with central umbilication. - Unlike other poxviruses, MCV replicates exclusively in the **cytoplasm** and causes a benign, self-limiting skin infection. *Herpesviruses* - Herpesviruses are also **DNA viruses** (e.g., HSV, VZV, EBV) but belong to the Herpesviridae family. - They are characterized by their ability to establish **lifelong latency** in neurons or lymphocytes. - They have an **icosahedral capsid** with an envelope, distinct from the brick-shaped morphology of poxviruses. - They typically cause vesicular lesions, not the umbilicated papules seen with MCV. *Picornaviruses* - Picornaviruses are **small, non-enveloped RNA viruses** (e.g., poliovirus, coxsackievirus, enteroviruses). - Their name reflects their small size ("pico" = small) and RNA genome. - Their genetic material is **positive-sense single-stranded RNA**, fundamentally different from the DNA genome of MCV. - They cause diverse infections including poliomyelitis, hand-foot-and-mouth disease, and the common cold. *Adenovirus* - Adenoviruses are **non-enveloped, double-stranded DNA viruses** with an **icosahedral capsid**. - They commonly cause respiratory infections, conjunctivitis, and gastroenteritis. - While they are DNA viruses, their morphology, replication strategy, and disease manifestations are distinct from the cutaneous lesions caused by MCV.
Question 1328: DNA polymerase of HBV is encoded by which of the following ?
- A. S gene
- B. C gene
- C. P gene (Correct Answer)
- D. X gene
Explanation: ***P gene*** - The **P gene** (polymerase gene) of the **Hepatitis B virus (HBV)** encodes for the viral DNA polymerase. - This enzyme is crucial for HBV replication, as it functions as both a **reverse transcriptase** and a **DNA-dependent DNA polymerase**. *S gene* - The **S gene** encodes for the **surface antigens (HBsAg)** of HBV, which are involved in viral entry and are the primary targets of the host immune response. - It does not encode for the viral polymerase. *C gene* - The **C gene** encodes for the **HBV core antigen (HBcAg)**, which forms the viral nucleocapsid. - It also produces the **e antigen (HBeAg)**, which is a secreted protein indicating active viral replication. *X gene* - The **X gene** encodes for the **HBV X protein (HBxAg)**, which is a regulatory protein involved in viral transcription and replication. - It plays a role in **hepatocarcinogenesis** but does not encode the polymerase enzyme.
Question 1329: What is the window period in HIV infection?
- A. > 12 weeks
- B. 8-12 weeks
- C. 4-8 weeks
- D. 2-4 weeks (Correct Answer)
Explanation: ***2-4 weeks*** - The **window period** in HIV infection is the time between initial infection and when a **detectable immune response** can be measured by standard testing. - Modern **4th generation Ag/Ab combination tests** (now standard in most settings) detect both **HIV p24 antigen** and **HIV antibodies**, reducing the window period to **18-45 days (approximately 2-4 weeks)**. - During this phase, individuals are highly infectious, and early testing with 4th generation tests provides the earliest reliable detection. - **HIV RNA/PCR tests** can detect even earlier (10-14 days) but are not routinely used for initial screening. *4-8 weeks* - This represents the window period for **older 3rd generation antibody-only tests**, which are no longer the standard screening method in most clinical settings. - While historically accurate, this timeframe is outdated with current **4th generation testing protocols**. *8-12 weeks* - This extended period may apply to some **point-of-care rapid tests** or in cases with delayed seroconversion, but exceeds the typical window for standard laboratory-based 4th generation tests. - Most individuals will have detectable antibodies well before this timeframe with modern testing. *> 12 weeks* - By this point, nearly all infected individuals would have developed detectable antibodies with any test generation. - A negative test after 12 weeks essentially **rules out HIV infection** (assuming no recent high-risk exposures). - This is well beyond the **window period** for all standard HIV testing methods.
Question 1330: Among the following, which is the smallest virus?
- A. Herpes virus
- B. Adenovirus
- C. Parvovirus (Correct Answer)
- D. Poxvirus
Explanation: ***Parvovirus*** - **Parvoviruses** are among the smallest viruses, typically measuring around **18-26 nanometers** in diameter. - They are unique in having a **single-stranded DNA genome**. *Herpes virus* - **Herpesviruses** are relatively large, **double-stranded DNA viruses** with diameters ranging from **150-200 nanometers**. - They are known for establishing **latent infections** in the host. *Adenovirus* - **Adenoviruses** are medium-sized, **non-enveloped, icosahedral viruses** with **double-stranded DNA genomes**, typically 70-90 nanometers in diameter. - They are a common cause of respiratory, gastrointestinal, and ocular infections. *Poxvirus* - **Poxviruses** are exceptionally large and complex viruses, measuring approximately **200-400 nanometers** in length, and are visible under a light microscope. - They have a unique **brick-shaped morphology** and a **double-stranded DNA genome**.
Practice by Chapter
Virus Structure and Classification
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Viral Replication
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Pathogenesis of Viral Infections
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DNA Viruses: Herpesviruses
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DNA Viruses: Poxviruses and Adenoviruses
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Hepatitis Viruses
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RNA Viruses: Orthomyxoviruses
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RNA Viruses: Paramyxoviruses
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Enteroviruses and Rhinoviruses
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Arboviruses
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HIV and Retroviruses
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Oncogenic Viruses
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