Virology — MCQs

Virology Indian Medical PG Practice Questions and MCQs

Question 1381: Which of the following viruses specifically targets CD4+ T lymphocytes leading to progressive immunodeficiency?

A. Adenovirus
B. Herpes virus
C. CMV
D. HIV (Correct Answer)

Explanation: ***HIV*** - **HIV** primarily targets **CD4+ T lymphocytes**, which are crucial components of the immune system found in lymphoid tissue. - The virus binds to CD4 receptors (along with co-receptors CCR5 or CXCR4) and progressively destroys these cells. - This progressive destruction leads to **immunodeficiency** and the development of AIDS. - HIV's specific tropism for CD4+ T cells distinguishes it from other viruses. *Adenovirus* - **Adenovirus** can infect various cell types, including respiratory epithelium, conjunctival cells, and gastrointestinal tract cells. - It does not have specific tropism for CD4+ T lymphocytes. - While it can cause opportunistic infections in immunocompromised individuals, it does not target T cells specifically. *Herpes virus* - **Herpes viruses** (e.g., HSV, VZV) primarily establish **latency in sensory neurons**. - EBV (a herpes virus) does target B lymphocytes, but not CD4+ T cells. - They do not cause progressive immunodeficiency through CD4+ T cell destruction. *CMV* - **CMV** (Cytomegalovirus) infects a wide range of cell types including fibroblasts, epithelial cells, endothelial cells, and monocytes. - While it can affect immunocompromised individuals, it does not specifically target CD4+ T lymphocytes. - CMV does not cause progressive immunodeficiency through selective CD4+ T cell destruction.

Question 1382: HIV was discovered in what year?

A. 1983 (Correct Answer)
B. 1975
C. 1995
D. 1985

Explanation: ***1983*** - HIV (Human Immunodeficiency Virus) was definitively identified and recognized as the cause of AIDS by **Luc Montagnier** at the Institut Pasteur in Paris. - This discovery was crucial for understanding the pathogenesis of AIDS and developing diagnostic tests. *1975* - While documented cases of AIDS occurred in the 1970s, the **virus itself had not yet been identified** in 1975. - Research into rare opportunistic infections and cancers linked to immune deficiency was just beginning to gather momentum. *1995* - By 1995, significant progress had been made in understanding HIV, including the development of **highly active antiretroviral therapy (HAART)**, which revolutionized AIDS treatment. - The initial discovery of the virus happened much earlier. *1985* - In 1985, the first **HIV antibody test** was approved, allowing for widespread screening of blood products and diagnosis of infection. - This was a significant advancement, but it followed the initial discovery of the virus a few years prior.

Question 1383: Most common organism causing laryngotracheobronchitis is:

A. RSV
B. Parainfluenzavirus (Correct Answer)
C. Influenza virus
D. H. influenzae

Explanation: ***Parainfluenzavirus*** - **Parainfluenza viruses** (PIVs), particularly PIV-1 and PIV-2, are the **most common causes of croup** (laryngotracheobronchitis) in children. - They primarily cause inflammation and swelling of the **larynx, trachea, and bronchi**, leading to the characteristic **barking cough** and stridor. *RSV* - **Respiratory Syncytial Virus (RSV)** is the **most common cause of bronchiolitis** and pneumonia in infants and young children. - While it can cause upper respiratory symptoms, it is less frequently the primary cause of croup compared to parainfluenza viruses. *Influenza virus* - **Influenza virus** typically causes **influenza** (the flu), which presents with more systemic symptoms like high fever, body aches, and fatigue. - Although influenza can lead to severe respiratory complications, it is a less common cause of isolated laryngotracheobronchitis. *H. influenzae* - **_Haemophilus influenzae_** type b (Hib) was historically a major cause of **epiglottitis**, a severe and life-threatening infection of the epiglottis. - With widespread vaccination, Hib infections are rare, and it is not a common cause of laryngotracheobronchitis.

Question 1384: Which is the most common causative organism involved in infections after kidney transplantation?

A. Klebsiella
B. Epstein Barr virus
C. Cytomegalovirus (Correct Answer)
D. Herpes simplex virus

Explanation: ***Cytomegalovirus*** - **Cytomegalovirus (CMV)** is the most common opportunistic infection after kidney transplantation, occurring in **50-80%** of transplant recipients. - CMV infection or reactivation typically occurs **1-6 months post-transplant** due to intense **immunosuppression** required to prevent graft rejection. - Highest risk is in **donor-positive/recipient-negative (D+/R-)** serostatus, but reactivation can occur in seropositive recipients. - CMV can cause **fever, leukopenia, graft dysfunction**, and invasive disease affecting multiple organ systems. *Klebsiella* - While *Klebsiella* can cause serious bacterial infections, particularly **urinary tract infections** and **pneumonia** in transplant patients, it is not the most common overall causative organism for post-transplant infections. - Bacterial infections like *Klebsiella* are often related to indwelling catheters or surgical sites but are less ubiquitous than viral reactivations in immunosuppressed patients. *Epstein Barr virus* - **Epstein-Barr Virus (EBV)** is another significant viral pathogen in transplant recipients, primarily associated with **post-transplant lymphoproliferative disorder (PTLD)**. - While important, EBV infection or reactivation is not as universally prevalent or as frequently symptomatic as CMV in the post-transplant period. *Herpes simplex virus* - **Herpes simplex virus (HSV)** can cause infections in transplant patients, leading to **mucocutaneous lesions** and occasionally disseminated disease. - HSV infections are generally less severe and less common than CMV, which can affect multiple organ systems and has a higher morbidity burden in this population.

Question 1385: Japanese encephalitis is caused by which virus?

A. Human retrovirus
B. Arboviruses (Correct Answer)
C. Enteroviruses
D. Cytomegalovirus

Explanation: ***Arboviruses*** - Japanese encephalitis virus is a **flavivirus**, which belongs to the larger group of **arboviruses**. - **Arboviruses** are viruses transmitted by arthropod vectors, such as mosquitoes, which is how Japanese encephalitis spreads. *Human retrovirus* - **Retroviruses** include viruses like HIV, which are characterized by their ability to reverse-transcribe RNA into DNA. - They are not associated with encephalitis transmitted by insect vectors. *Enteroviruses* - **Enteroviruses** primarily replicate in the gastrointestinal tract and can cause a range of illnesses, including meningitis and hand-foot-and-mouth disease. - They are typically spread via the fecal-oral route, not through mosquito bites. *Cytomegalovirus* - **Cytomegalovirus (CMV)** is a herpesvirus that can cause infections in people of all ages, often asymptomatic but particularly severe in immunocompromised individuals and neonates. - CMV is transmitted through close contact, not via arthropod vectors.

Question 1386: Which one of the following is a function of the enzyme reverse transcriptase, which is unique to retroviruses?

A. DNase activity
B. RNA-dependent RNA polymerase activity
C. RNA isomerase activity
D. RNA-dependent DNA polymerase activity (Correct Answer)

Explanation: ***RNA-dependent DNA polymerase activity*** - **Reverse transcriptase** is a unique enzyme found in retroviruses that synthesizes **DNA from an RNA template**, hence its name "reverse" transcriptase. - This activity is crucial for the retroviral life cycle, as it allows the viral **RNA genome** to be reverse-transcribed into **DNA**, which can then integrate into the host cell's genome. *DNase activity* - **DNase** (deoxyribonuclease) enzymes degrade DNA. This activity is not a primary function of reverse transcriptase. - While integration of the viral DNA into the host genome involves DNA manipulation, the core reverse transcriptase enzyme does not exhibit DNase activity for its primary function. *RNA-dependent RNA polymerase activity* - This activity involves synthesizing **RNA from an RNA template**. It is characteristic of some **RNA viruses** (e.g., influenza virus), but not retroviruses. - Retroviruses use the host cell's machinery to transcribe their integrated DNA provirus into mRNA and new viral RNA genomes, rather than having their own RNA-dependent RNA polymerase. *RNA isomerase activity* - **RNA isomerase activity** is not a standard enzymatic function in the context of nucleic acid synthesis or modification performed by viral enzymes. - Isomerases typically rearrange atoms within a molecule. Reverse transcriptase's primary functions are polymerization and degradation of RNA/DNA hybrids, not isomerization.

Question 1387: The virus that causes aplastic anemia in chronic hemolytic diseases is

A. Adenovirus
B. Hepatitis virus
C. EB virus
D. Parvovirus (Correct Answer)

Explanation: ***Parvovirus*** - **Parvovirus B19** specifically targets and destroys **erythroid progenitor cells** in the bone marrow. - In patients with chronic hemolytic diseases (e.g., **sickle cell anemia**, **spherocytosis**), where red blood cell turnover is already high, this destruction leads to a severe, acute exacerbation of anemia known as an **aplastic crisis**. *Adenovirus* - Adenoviruses typically cause a range of illnesses, including **respiratory tract infections**, gastroenteritis, and conjunctivitis. - While they can cause severe illness in immunocompromised individuals, they are **not directly implicated** in causing aplastic anemia or aplastic crisis in chronic hemolytic diseases. *Hepatitis virus* - Hepatitis viruses (A, B, C, D, E) primarily cause **inflammation of the liver**. - Although severe viral infections can rarely trigger aplastic anemia, **hepatitis viruses are not the primary or common cause** of aplastic crisis in the context of chronic hemolytic disorders. *EB virus* - **Epstein-Barr virus (EBV)** is known for causing **infectious mononucleosis** and is associated with various lymphoproliferative disorders and malignancies. - While EBV can affect the bone marrow and, in rare instances, be linked to marrow suppression, it is **not the typical or direct cause** of aplastic crisis in chronic hemolytic conditions.

Question 1388: The following are true about Epstein-Barr virus (EBV) except which of the following?

A. Infects epithelial cells of pharynx
B. It is implicated in nasopharyngeal carcinoma
C. A member of herpes virus family
D. The main target of virus is the T-cell lymphocytes (Correct Answer)

Explanation: ***The main target of virus is the T-cell lymphocytes*** - This statement is incorrect because **Epstein-Barr virus (EBV)** primarily targets **B-lymphocytes**, not T-cell lymphocytes. - EBV infects B cells by binding to the **CD21 receptor** on their surface. *A member of herpes virus family* - **EBV** is indeed a member of the **Herpesviridae family**, specifically **gammaherpesvirus**. - Other common herpesviruses include **herpes simplex virus (HSV)** and **cytomegalovirus (CMV)**. *Infects epithelial cells of pharynx* - EBV initially infects and replicates in **epithelial cells of the oropharynx**, contributing to viral shedding in saliva. - This initial infection allows the virus to spread to the targeted B-lymphocytes. *It is implicated in nasopharyngeal carcinoma* - EBV is strongly associated with **nasopharyngeal carcinoma (NPC)**, particularly in endemic regions. - It is also linked to other malignancies like **Burkitt lymphoma** and **Hodgkin lymphoma**.

Question 1389: Which of the following statements about arboviruses is correct?

A. Kyasanur Forest Disease (KFD) was first identified in Kerala.
B. Dengue has only one serotype.
C. Chikungunya is transmitted by Aedes aegypti. (Correct Answer)
D. Yellow fever is endemic only in Asia.

Explanation: ***Chikungunya is transmitted by Aedes aegypti.*** - **Chikungunya virus** is primarily transmitted to humans through the bites of infected female **Aedes aegypti** and **Aedes albopictus** mosquitoes. - These mosquitoes are widespread in tropical and subtropical regions and are competent vectors for several arboviruses. *Dengue has only one serotype.* - Dengue virus has **four distinct serotypes** (DEN-1, DEN-2, DEN-3, and DEN-4), meaning infection with one serotype provides immunity to that serotype but not to the others. - Subsequent infection with a different serotype can lead to more severe disease, such as **Dengue Hemorrhagic Fever (DHF)** or **Dengue Shock Syndrome (DSS)**, due to antibody-dependent enhancement. *Kyasanur Forest Disease (KFD) was first identified in Kerala.* - **Kyasanur Forest Disease (KFD)** was first identified in the **Kyasanur Forest** of **Karnataka, India**, not Kerala, in 1957. - It is a **tick-borne hemorrhagic fever** caused by a flavivirus and is endemic to specific regions of India. *Yellow fever is endemic only in Asia.* - **Yellow fever** is endemic in **tropical and subtropical areas of South America and Africa**, not Asia. - The virus is transmitted to humans by infected **mosquitoes, primarily Aedes aegypti**.

Question 1390: Which of the following is a lentivirus?

A. HIV (Correct Answer)
B. HBV
C. HCV
D. Rabies virus

Explanation: ***Correct Answer: HIV*** - **HIV** (Human Immunodeficiency Virus) is the most well-known example of a **lentivirus**, a genus within the **Retroviridae** family. - Lentiviruses are characterized by a long incubation period before disease onset and the ability to cause chronic, slowly progressive diseases. - Key features of lentiviruses include: ability to infect non-dividing cells, integration into host genome, and causing persistent infections. *Incorrect: HBV* - **HBV** (Hepatitis B Virus) belongs to the **Hepadnaviridae** family, not the lentivirus family. - It is a **DNA virus** (not a retrovirus) that primarily infects the liver and can cause acute or chronic hepatitis. *Incorrect: HCV* - **HCV** (Hepatitis C Virus) is a member of the **Flaviviridae** family and is an **RNA virus**. - It is known for causing hepatitis and can lead to chronic infection, cirrhosis, and hepatocellular carcinoma. - Unlike lentiviruses, HCV does not use reverse transcriptase or integrate into the host genome. *Incorrect: Rabies virus* - The **rabies virus** is a member of the **Rhabdoviridae** family, specifically the genus *Lyssavirus*. - It is an **RNA virus** that causes acute encephalitis in mammals, including humans. - Unlike lentiviruses which cause chronic slow infections, rabies causes acute rapidly progressive disease.

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Virology — MCQs

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