Intro 3

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viral disease is dynamic - capacity for viruses to change

*viruses can adapt and change much faster than vaccines/vaccine design

Companion animals and race horses - travel world + increase spread

Shift in insect population - emergence of disease (blue tongue virus in UK)

Genetic changes occur during replication in host

Mutation - a change in the nucleotide sequence of a genome

Spontaneous mutation - viruses do not have proof reading mechanisms, errors are not corrected

Gene transfer between viruses - recombination + reassortment

Recombination - one or more genes transferred from one gene to another

Reassortment - entire genome segments are shuffled between virus's (new combination of segments)

Advantageous mutation = new strains can become established

*attenuated/weakened virus persists - goal of virulence but not kill

Antigenic Drift: spontaneous mutations in surface antigens - selection o variants in a partially immune population (accumulation of favourable mutations that allow persistence)

*result in emergence of new mutants in immune population - reason why vaccine strains need to be updated

Pigs are well infected with flu from different species - mixing pot, provide an opportunity for new assortments

as population becomes immune to influenza virus strain, variants which have altered antigenicity have selective growth advantage – antigenic drift/seasonal flu

variants with new HA and NA types (acquired through reassortment with avian flu viruses in mixing vessel, or direct transmission (rare) ) – antigenic drift

immunologically naïve population

surveillance of circulating strains : vaccines must be modified periodically to reflect currently circulating strains (WHO)

Summary:

Genetic mutation occurs during virus infection of cells

If conditions are appropriate new variants become selected and may dominate the population

Emerging mutants may have altered biology – potentially affected traits include pathogenicity, immunogenicity, drug resistance, host range

Virus mutation and other factors may lead to emergence of novel diseases which pose a threat to animal and human health