(SEM VIII) THEORY EXAMINATION 2022-23 VIROLOGY

SECTION A

(Attempt all – 2 marks each)

(a) Difference between viruses and bacteria

Viruses are acellular and can replicate only inside a living host cell, whereas bacteria are unicellular organisms that can grow independently.

(b) Viral envelope and its functions

The viral envelope is a lipid membrane surrounding some viruses. It helps in host cell attachment, entry, and protection of viral genetic material.

(c) Types of viral infections

Viral infections are classified as acute, chronic, latent, persistent, and slow infections.

(d) Symptoms of viral infection

Common symptoms include fever, fatigue, headache, muscle pain, cough, and inflammation depending on the virus.

(e) Classification of viruses

Viruses are classified based on chemical composition as DNA or RNA viruses and on replication strategy as positive-strand, negative-strand, or reverse-transcribing viruses.

(f) Virus nomenclature

Virus nomenclature is based on host, disease caused, morphology, genetic composition, and replication mechanism following ICTV guidelines.

(g) Positive vs negative strand RNA viruses

Positive-strand RNA viruses can act directly as mRNA, whereas negative-strand RNA viruses require RNA-dependent RNA polymerase for transcription.

(h) Reverse transcription

Reverse transcription is the process of synthesizing DNA from an RNA template, commonly seen in retroviruses.

(i) Characteristics of vaccines

Vaccines are safe, effective, stable, immunogenic, and capable of inducing long-term immunity.

(j) Adjuvant

An adjuvant is a substance added to vaccines to enhance immune response and improve vaccine effectiveness.

SECTION B

(Attempt any three – 10 marks each)

2(a) Methods of Virus Isolation

Viruses can be isolated using cell cultures, embryonated eggs, laboratory animals, and molecular techniques. Cell culture is the most common method as it allows observation of cytopathic effects.

2(b) Viral Defense Mechanisms Against Antibodies

Viruses evade antibodies through antigenic variation, latency, inhibition of antigen presentation, and production of decoy proteins.

2(c) RNA vs DNA Viruses & Large DNA Viruses

RNA viruses mutate rapidly and replicate in cytoplasm, whereas DNA viruses replicate mostly in nucleus. Large DNA viruses include poxvirus and herpesvirus with complex replication cycles.

2(d) Viruses vs Retroviruses

Retroviruses contain RNA and use reverse transcription to form DNA. Their structure includes envelope, capsid, RNA genome, and reverse transcriptase. Retroviral vectors are used in gene therapy.

2(e) Antiviral Interferons and Antivirals

Interferons inhibit viral replication and enhance immune response. Antivirals block viral entry, replication, or release from host cells.

SECTION C

3(a) Structure of Virus and Capsids

A virus consists of nucleic acid genome, capsid, and sometimes an envelope. Capsids are helical, icosahedral, or complex in structure and protect viral genetic material.

4(a) Viral Infection and Life Cycle

Viral infection involves attachment, penetration, uncoating, replication, assembly, and release of new viral particles from host cells.

5(a) Dengue Virus

Dengue virus is an enveloped RNA virus transmitted by Aedes mosquito. It replicates in host cells and causes dengue fever with symptoms like fever, rash, and joint pain.

6(a) Influenza Virus

Influenza virus is an enveloped RNA virus with segmented genome. It undergoes antigenic drift and shift and infects respiratory epithelial cells.

7(b) Types of Vaccines and Viral Disease Treatment

Vaccines include live attenuated, inactivated, subunit, DNA, and mRNA vaccines. Viral diseases are treated mainly through vaccines because antibiotics are ineffective against viruses.