Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 1311: Which gene encodes the core antigen (HBcAg) in the Hepatitis B virus (HBV)?

A. S gene
B. C gene (Correct Answer)
C. P gene
D. X gene

Explanation: ***C gene (Correct)*** - The **C gene** (Core gene) of the Hepatitis B virus is responsible for encoding the **HBcAg (Hepatitis B core antigen)**. - This antigen forms the **nucleocapsid** of the virus, encapsulating the viral DNA and polymerase. - HBcAg is found in the hepatocyte nucleus and is a marker of active viral replication. *S gene* - The S gene encodes the **HBsAg (Hepatitis B surface antigen)**, which is the major component of the viral envelope. - HBsAg is critical for viral attachment and entry into host cells and is the primary antigen used in HBV vaccination. - This is a marker of HBV infection and is used for screening. *P gene* - The P gene encodes the **HBV polymerase**, an enzyme with both reverse transcriptase and DNA polymerase activities. - This polymerase is essential for viral replication, converting the pregenomic RNA into DNA. - It is the largest gene in the HBV genome. *X gene* - The X gene encodes the **HBx protein**, a small promiscuous protein known to be a transcriptional transactivator. - HBx plays a role in viral replication, gene expression, and is implicated in the development of **hepatocellular carcinoma**. - This is the smallest gene in the HBV genome.

Question 1312: Ebola virus belongs to?

A. Picornaviridae
B. Togaviridae
C. Flaviviridae
D. Filoviridae (Correct Answer)

Explanation: ***Filoviridae*** - The **Ebola virus** is a member of the family **Filoviridae**, which includes highly pathogenic viruses known for causing severe hemorrhagic fevers. - Viruses in this family typically have a **filamentous** or thread-like morphology, which is how they get their name ("filo" means thread-like). ***Picornaviridae*** - This family includes viruses like *poliovirus* and *rhinoviruses*, which are generally known for causing respiratory or gastrointestinal illnesses, not hemorrhagic fever. - Picornaviruses are characterized by being very small, non-enveloped RNA viruses. ***Togaviridae*** - This family includes viruses such as *rubella virus* and *alphaviruses* (e.g., Eastern equine encephalitis virus), which are often transmitted by arthropods and cause conditions like rash, arthritis, or encephalitis. - Togaviruses are enveloped RNA viruses with a single-stranded, positive-sense RNA genome. ***Flaviviridae*** - This family includes viruses like *dengue virus*, *Zika virus*, and *yellow fever virus*, which are typically transmitted by mosquitoes or ticks and can cause hemorrhagic manifestations or neurological symptoms. - Flaviviruses are enveloped RNA viruses with a single-stranded, positive-sense RNA genome, but they do not cause Ebola-like hemorrhagic fever.

Question 1313: Capsid of viral structure is:

A. Extracellular infectious particle
B. Protein coat around nucleic acid (Correct Answer)
C. Envelope around a virus
D. None of the above

Explanation: ***Protein coat around nucleic acid*** - The **capsid** is a protective protein shell that encloses the viral **genetic material** (either **DNA or RNA**). - It plays a crucial role in protecting the viral genome from nucleases and aids in attaching the **virion** to host cells. *Extracellular infectious particle* - An **extracellular infectious particle** refers to the entire **virion**, which includes the capsid and its enclosed nucleic acid, and sometimes an envelope. - The **capsid** is only one component of the **virion**, not the entire particle itself. *Envelope around a virus* - The **envelope** is an outer **lipid bilayer** derived from the host cell membrane that surrounds some, but not all, viruses. - The **capsid** is located *inside* the envelope in enveloped viruses, or forms the outermost layer in non-enveloped viruses. *None of the above* - This option is incorrect because **"Protein coat around nucleic acid"** accurately defines the **capsid**.

Question 1314: Which is the most common influenza virus type causing disease in humans?

A. Type A (Correct Answer)
B. Type B
C. Type C
D. Type D

Explanation: ***Type A*** - **Influenza A virus** is responsible for the majority of human influenza cases and is the only type known to cause **pandemics**. - Its ability to undergo **antigenic shift** results in new viral subtypes that can evade existing immunity, leading to widespread outbreaks. *Type B* - **Influenza B virus** causes regional epidemics, but its genetic variability is less pronounced than Type A, meaning it does not typically cause pandemics. - While it can cause significant illness and fatalities, especially in young children and the elderly, it is generally less common than influenza A. *Type C* - **Influenza C virus** is generally associated with very mild respiratory illnesses and is not thought to cause epidemics or pandemics. - Infections are usually asymptomatic or cause only minor cold-like symptoms. *Type D* - **Influenza D virus** primarily affects pigs and cattle and is not known to cause disease in humans. - It is distinct from human influenza viruses and does not contribute to human influenza seasonal outbreaks.

Question 1315: Which of the following statements about Cytomegalovirus (CMV) is incorrect?

A. Most common cause of transplacental infection
B. A non-enveloped DNA virus (Correct Answer)
C. Produces intranuclear inclusions
D. Most common cause of post-transplantation infection

Explanation: ***A non-enveloped DNA virus*** - CMV is a **herpesvirus**, which are characterized by being **enveloped DNA viruses**. This statement is incorrect as it claims CMV is non-enveloped. - The viral envelope is crucial for **entry into host cells** and evasion of the immune system. *Most common cause of transplacental infection* - CMV is indeed the **most common viral cause** of congenital infections, transmitted vertically from mother to fetus. - Congenital CMV can lead to various complications, including **hearing loss** and **neurological deficits**. *Produces intranuclear inclusions* - CMV infection is characterized by the presence of **"owl's eye" intranuclear inclusions** in infected cells. - These inclusions are a **histopathological hallmark** used in the diagnosis of CMV infection. *Most common cause of post-transplantation infection* - CMV is a significant opportunistic pathogen in **immunocompromised individuals**, especially after organ transplantation. - It can cause a range of symptoms, from **fever and malaise** to severe organ damage, such as pneumonitis and gastroenteritis, in transplant recipients.

Question 1316: Hand foot mouth disease is caused by ?

A. Enterovirus 70
B. Coxsackievirus A (Correct Answer)
C. Coxsackievirus B
D. Enterovirus

Explanation: ***Coxsackievirus A*** - Hand-foot-and-mouth disease (HFMD) is most commonly caused by **Coxsackievirus A16** and occasionally other **Coxsackievirus A serotypes** (especially **Enterovirus A71** in Asia). - This virus belongs to the **Enterovirus genus** and is responsible for the characteristic vesicular rash on hands, feet, and mouth. *Enterovirus 70* - **Enterovirus 70** is primarily associated with **acute hemorrhagic conjunctivitis** and, less commonly, **acute flaccid paralysis**. - It is not the causative agent for Hand-Foot-and-Mouth Disease. *Coxsackievirus B* - **Coxsackievirus B** serotypes are known for causing illnesses like **pleurodynia**, **myocarditis**, and **pericarditis**. - While also an enterovirus, it is not the primary cause of Hand-Foot-and-Mouth Disease. *Enterovirus* - **Enterovirus** is a broad genus of viruses, encompassing **Coxsackieviruses**, **echoviruses**, and **polioviruses**. - While Coxsackievirus A is an enterovirus, simply stating "Enterovirus" is too general and less specific than the correct answer.

Question 1317: Which of the following is Hepadnavirus?

A. HAV
B. HBV (Correct Answer)
C. HCV
D. HDV

Explanation: ***HBV*** - **HBV (Hepatitis B Virus)** is the prototypical member of the Hepadnaviridae family. - Hepadnaviruses are unique in that they are **DNA viruses** that replicate through an **RNA intermediate** using reverse transcriptase. *HAV* - **HAV (Hepatitis A Virus)** belongs to the Picornaviridae family, which are **small, non-enveloped RNA viruses**. - It is transmitted via the **fecal-oral route** and causes acute hepatitis. *HCV* - **HCV (Hepatitis C Virus)** is a member of the Flaviviridae family, characterized by being an **enveloped, positive-sense single-stranded RNA virus**. - It primarily causes **chronic hepatitis** and is transmitted parenterally. *HDV* - **HDV (Hepatitis D Virus)** is a **defective RNA virus** that requires co-infection with HBV for replication. - It is classified in the genus **Deltavirus** and is a **satellite virus** of HBV, not a member of Hepadnaviridae.

Question 1318: Which of the following statements about Rhabdoviridae is false?

A. Contains enveloped viruses with helical nucleocapsid
B. Rabies virus is inactivated by formalin
C. Rabies virus is negative sense double stranded RNA virus (Correct Answer)
D. Includes vesiculostomatitis virus

Explanation: ***Rabies virus is negative sense double stranded RNA virus*** - This statement is **false** because **Rhabdoviridae**, including the rabies virus, are **negative-sense single-stranded RNA viruses**, not double-stranded. - The genome is a single molecule of **linear, non-segmented RNA**. *Contains enveloped viruses with helical nucleocapsid* - This statement is **true** as Rhabdoviridae are characterized by their **bacilliform (bullet-shaped)** morphology, possessing an **envelope** and a **helical nucleocapsid**. - The envelope is derived from the host cell membrane, and the nucleocapsid houses the viral RNA genome. *Rabies virus is inactivated by formalin* - This statement is **true** because **formalin (formaldehyde)** is a strong chemical agent commonly used to inactivate viruses for vaccine production, including the rabies virus. - Formalin denatures viral proteins and nucleic acids, rendering the virus non-infectious while preserving its antigenicity. *Includes vesiculostomatitis virus* - This statement is **true** because **vesicular stomatitis virus (VSV)** is a well-known member of the **Rhabdoviridae** family. - VSV is often used as a model system for studying rhabdoviruses due to its relatively simple genome and ease of manipulation in the lab.

Question 1319: What is the most clinically significant common characteristic of rotavirus and Norwalk virus?

A. Both are RNA viruses
B. Both are transmitted via contaminated food or water
C. Both are causes of viral gastroenteritis (Correct Answer)
D. Both can cause outbreaks in closed communities

Explanation: ***Both are causes of viral gastroenteritis*** - **Rotavirus** and **Norwalk virus** (now typically referred to as norovirus) are the leading causes of acute viral gastroenteritis worldwide, affecting both children and adults. - This condition is characterized by symptoms such as **diarrhea**, **vomiting**, **abdominal pain**, and fever. *Both are RNA viruses* - While **Rotavirus is an RNA virus**, specifically a double-stranded RNA virus, the Norwalk virus (norovirus) is also an RNA virus, but it's a single-stranded RNA virus. Therefore, this statement is factually correct, but less specific as a "common characteristic" of their clinical relevance. - The shared clinical outcome of causing gastroenteritis is a more direct and common characteristic for comparing these pathogens in a medical context. *Both are transmitted via contaminated food or water* - While both viruses can be transmitted through **contaminated food and water** (fecal-oral route), this is not their exclusive mode of transmission. - **Norovirus** is highly contagious and often spreads person-to-person or via contaminated surfaces, and **rotavirus** can also spread through direct contact in addition to contaminated sources. *Both can cause outbreaks in closed communities* - While both viruses can indeed cause **outbreaks in closed communities** like cruise ships, daycares, and nursing homes, this is a consequence of their highly contagious nature and fecal-oral transmission, rather than their most fundamental shared characteristic. - The primary medical characteristic they share is their role as causative agents of **viral gastroenteritis**.

Question 1320: Which of the following conditions is NOT typically caused by Respiratory Syncytial Virus (RSV)?

A. Upper respiratory tract infection in children (coryza).
B. Lower respiratory tract infection (bronchitis).
C. Mild cold-like symptoms.
D. Severe lung condition (ARDS). (Correct Answer)

Explanation: ***Severe lung condition (ARDS)*** - While RSV can cause severe respiratory illness, **Acute Respiratory Distress Syndrome (ARDS)** is a less typical direct consequence of RSV infection, especially in healthy individuals. - ARDS is characterized by **widespread inflammation** in the lungs leading to fluid accumulation and severe oxygenation impairment, which is more commonly associated with septic shock, pneumonia from severe bacterial or other viral infections, or aspiration. *Upper respiratory tract infection in children (coryza)* - **Coryza** (common cold symptoms like runny nose, sneezing, and watery eyes) is a very common initial presentation of **RSV infection**, particularly in infants and young children. - RSV frequently causes **upper respiratory symptoms** before progressing to lower respiratory tract involvement in some cases. *Lower respiratory tract infection (bronchitis)* - RSV commonly causes **bronchitis** (inflammation of the bronchi) in children and can lead to **bronchiolitis** (inflammation of the smaller bronchioles), with RSV being the **leading cause of bronchiolitis** in infants under 2 years of age. - RSV can also cause **pneumonia**, making it an important cause of lower respiratory tract infections, especially in vulnerable populations like infants, elderly, and immunocompromised individuals. *Mild cold-like symptoms* - In older children and adults, RSV infection often manifests as **mild, self-limiting cold-like symptoms**, similar to a common cold. - These symptoms typically include a stuffy nose, sore throat, cough, and low-grade fever, which resolve within a week or two.

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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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Virology — MCQs

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