(SEM VIII) THEORY EXAMINATION 2021-22 VIROLOGY

SECTION A

(Attempt all questions in brief | 2 × 7 = 14 marks)

(a) Define virus

A virus is a submicroscopic infectious agent composed of nucleic acid (DNA or RNA) enclosed in a protein coat, which can replicate only inside a living host cell.

(b) What do you understand by purification of virus?

Purification of virus is the process of separating virus particles from host cell debris and contaminants using techniques like centrifugation, filtration, and chromatography to obtain a pure viral preparation.

(c) Define viral infection

Viral infection is the process by which a virus enters a host cell, replicates inside it, and causes disease or cellular damage.

(d) What is a macromolecule?

A macromolecule is a large biological molecule such as proteins, nucleic acids, carbohydrates, or lipids that play essential roles in cellular structure and function.

(e) Define antiviral

An antiviral is a drug or agent that inhibits the growth, replication, or activity of viruses without harming host cells.

(f) What are ribozymes?

Ribozymes are RNA molecules with enzymatic activity that can catalyze specific biochemical reactions, such as RNA cleavage.

(g) What do you mean by pathogen?

A pathogen is any microorganism or biological agent (virus, bacteria, fungi, parasite) that causes disease in a host.

SECTION B

(Attempt ANY THREE | 7 × 3 = 21 marks)

2(a) Isolation of virus and its components

Isolation of virus refers to separating viruses from infected tissues or fluids. This is done using techniques such as filtration, centrifugation, and cell culture.
Viral components like nucleic acid and capsid proteins can be isolated using chemical extraction and enzymatic methods. Isolation helps in diagnosis, vaccine development, and research.

2(b) Effect of virus on host macromolecules

Viruses alter host macromolecules to favor their replication. They suppress host protein synthesis and redirect cellular machinery to produce viral proteins.
Host DNA replication may be inhibited, RNA synthesis altered, and normal metabolic pathways disrupted, leading to cell damage or death.

2(c) Flavi viruses with examples

Flaviviruses are enveloped, positive-sense single-stranded RNA viruses belonging to the family Flaviviridae.
They are mainly transmitted by mosquitoes and ticks.
Examples include Dengue virus, Zika virus, Yellow fever virus, and West Nile virus.
These viruses cause fever, hemorrhagic symptoms, and neurological disorders.

2(d) dsRNA viruses with examples

Double-stranded RNA (dsRNA) viruses contain RNA as their genetic material in double-stranded form.
They belong mainly to the Reoviridae family.
Examples include Rotavirus, which causes severe diarrhea in children, and Bluetongue virus.
They replicate in the cytoplasm and possess segmented genomes.

2(e) QA/QS issues in large-scale vaccine manufacturing

Quality Assurance (QA) ensures proper manufacturing practices, documentation, and compliance with regulations.
Quality Control (QC) tests vaccine purity, potency, sterility, and safety.
Challenges include contamination control, batch consistency, cold-chain maintenance, and regulatory compliance to ensure vaccine safety and effectiveness.

SECTION C

3(a) History of viruses

Viruses were first discovered in the late 19th century. In 1892, Dmitri Ivanovsky showed that tobacco mosaic disease was caused by a filterable agent. Later, Beijerinck named it “virus.”
Advancements in electron microscopy and molecular biology helped understand viral structure, replication, and genetics.

3(b) Shapes and sizes of viruses

Viruses show various shapes such as helical, icosahedral, spherical, and complex.
Their sizes range from 20 nm to 300 nm. For example, poliovirus is small and spherical, while bacteriophages have complex shapes.

4(a) Virus counterattack mechanisms with examples

Viruses evade host immunity through mechanisms like antigenic variation, inhibition of interferon response, and latency.
For example, HIV mutates rapidly to escape immune detection, while Herpes virus remains latent in host cells.

4(b) Viral diagnostic technique – ELISA

ELISA (Enzyme-Linked Immunosorbent Assay) detects viral antigens or antibodies using enzyme-linked antibodies.
It is widely used for diagnosing infections like HIV, Hepatitis B, and COVID-19 due to its high sensitivity and specificity.

5(a) Positive-strand viruses and their identification

Positive-strand RNA viruses have RNA that acts directly as mRNA.
They are identified by their ability to synthesize proteins immediately after infection.
Examples include Poliovirus, Dengue virus, and Coronavirus.

5(b) SARS family of viruses

SARS viruses belong to the Coronavirus family.
They are enveloped, positive-strand RNA viruses causing severe respiratory illness.
Examples include SARS-CoV, MERS-CoV, and SARS-CoV-2.

6(a) Negative-strand viruses and Retroviruses (HIV)

Negative-strand viruses have RNA complementary to mRNA and require RNA polymerase for transcription. Example: Influenza virus.
Retroviruses like HIV use reverse transcriptase to convert RNA into DNA, which integrates into the host genome.

6(b) Reverse transcription

Reverse transcription is the process of converting viral RNA into DNA using the enzyme reverse transcriptase.
This DNA is integrated into the host genome, allowing viral replication. This mechanism is characteristic of retroviruses.

7(a) DNA vaccines

DNA vaccines use plasmid DNA encoding viral antigens. When injected, host cells produce antigens, stimulating immune response.
They are stable, safe, and easy to produce.

7(b) Modern approaches of virus control

Modern virus control includes vaccination, antiviral drugs, gene therapy, RNA interference, monoclonal antibodies, and public health measures like sanitation and surveillance.