(SEM VIII) THEORY EXAMINATION 2023-24 VIROLOGY

SECTION A

(2 × 10 = 20 | Very Short Answers)

a. How are viruses named and classified?
Viruses are named based on disease caused, host, morphology, genetic material, or discoverer. They are classified by genome type, capsid symmetry, envelope presence, and replication strategy.

b. Characteristics of a virus
Viruses are acellular, obligate intracellular parasites, contain either DNA or RNA, lack metabolic machinery, and replicate only inside living host cells.

c. Effect of virus disease on animals
Viral diseases in animals cause fever, weakness, reduced productivity, organ damage, immunosuppression, and sometimes death.

d. Virus’ counter attack
Virus counter attack refers to viral strategies that evade host immune responses, such as antigenic variation, latency, and inhibition of immune signaling.

e. Point of virus taxonomy
Virus taxonomy helps in identification, classification, understanding evolutionary relationships, disease diagnosis, and development of vaccines and treatments.

f. Life cycle of Picornavirus
Picornavirus enters host cell, releases RNA, synthesizes viral proteins, replicates RNA, assembles new virions, and releases them by cell lysis.

g. Diseases caused by Enterovirus
Enteroviruses cause poliomyelitis, hand-foot-mouth disease, viral meningitis, myocarditis, and encephalitis.

h. Composition of Orthomyxovirus virion
Orthomyxoviruses contain segmented negative-sense RNA, nucleoprotein, matrix protein, lipid envelope, and surface glycoproteins hemagglutinin and neuraminidase.

i. Three major modes of action of antiviral drugs
Antivirals inhibit viral entry, block viral replication, or prevent viral assembly and release.

j. Do antivirals have side effects?
Yes, antivirals may cause nausea, headache, fatigue, liver toxicity, or allergic reactions depending on the drug.

SECTION B

(Attempt any THREE | 3 × 10 = 30 Marks)

2(a) Virus purification through precipitation

Virus purification by precipitation involves concentrating viruses using chemicals like ammonium sulfate or polyethylene glycol (PEG). These agents reduce virus solubility, causing aggregation and precipitation. The precipitate is separated by centrifugation and further purified, helping remove cellular debris and contaminants.

2(b) Survival of viruses in a dead body

Virus survival in a dead body depends on temperature, humidity, virus type, and tissue environment. Some viruses survive for hours, while others like hepatitis or Ebola can persist for days under favorable conditions. Cold temperatures prolong survival, whereas heat and desiccation reduce viability.

2(c) Transmission of SARS and prevention

SARS spreads through respiratory droplets, close contact, contaminated surfaces, and aerosols.
Preventive steps include wearing masks, hand hygiene, social distancing, ventilation, isolation of infected individuals, and vaccination.

2(d) Life cycle of Paramyxovirus & pathogenic types

Paramyxovirus enters host cells via membrane fusion, releases RNA, undergoes transcription and replication in the cytoplasm, assembles, and buds from the host membrane.
Pathogenic types include measles virus, mumps virus, respiratory syncytial virus, and Newcastle disease virus.

2(e) Effect of antivirals on immune system

Antivirals reduce viral load, allowing the immune system to recover and respond effectively. Some antivirals enhance immune response, while others may suppress immune functions if misused.

SECTION C

3(a) Viruses as a link between living and non-living

Viruses show non-living traits outside the host, such as lack of metabolism and crystallization. Inside host cells, they show living traits like replication, mutation, and evolution. Hence, viruses are considered a connecting link between living and non-living entities.

3(b) Components of viruses and host specificity

Viruses consist of nucleic acid, capsid, envelope (in some), and enzymes.

Nucleic acid determines genetic identity

Capsid protects genome and aids attachment

Envelope proteins decide host specificity and cell entry
Each component influences infectivity and host range.

4(a) Why plant and bacterial viruses are non-enveloped

Plant and bacterial viruses lack envelopes because they must survive harsh environments like soil and plant sap. Non-enveloped capsids provide greater stability and resistance to environmental stress.

4(b) Detection of COVID-19 using Real-Time RT-PCR

Real-Time RT-PCR detects SARS-CoV-2 RNA by converting viral RNA into complementary DNA using reverse transcriptase. The DNA is amplified using specific primers, and fluorescent signals indicate viral presence in real time.

5(a) Classification of Picornavirus

Picornaviridae are classified into genera such as:

Enterovirus (Poliovirus, Coxsackievirus)                      Rhinovirus (Common cold virus)

Hepatovirus (Hepatitis A virus)

Explanation:
Enteroviruses infect the gastrointestinal tract and nervous system, while Rhinoviruses infect the respiratory tract.

5(b) RNA primer used in reverse transcription

Reverse transcription uses tRNA primers or synthetic primers like oligo-dT to initiate DNA synthesis from viral RNA.

6(a) Spread of avian influenza & human infection

Avian influenza spreads among birds through direct contact and contaminated surfaces. Humans get infected through close contact with infected birds, secretions, or improperly cooked poultry.

6(b) Rabies incubation and survival

Rabies incubation in dogs and cats ranges from 2 weeks to several months. Once symptoms appear, the animal usually survives 7–10 days before death.

7(a) DNA vaccine vs Recombinant vaccine

DNA vaccines introduce genetic material encoding antigen into host cells, inducing immune response.
Recombinant vaccines use genetically engineered proteins as antigens. DNA vaccines offer longer immunity, while recombinant vaccines are safer and well-established.

7(b) Antiviral screening & antisense RNA vaccines

Antiviral screening identifies compounds that inhibit viral replication using cell-based assays and libraries.
Antisense RNA and ribozymes block viral gene expression by binding viral RNA, preventing protein synthesis and replication.