INFLUENZA



INFLUENZA

• Caused by a myxovirus - RNA virus

• Spread by droplet infection

• Infection confined to the respiratory tract - there is no viraemia

• Incubation period 1-3 days

Three types

• Influenza A: causes epidemics and pandemics; has a reservoir in birds, undergoes antigenic shift - sudden major change in antigenicity based on recombination between different strains

• Influenza B: causes epidemics. No animal reservoir

• Influenza C: causes mild illness only

• Virus envelope has haemagglutinin and neuraminidase antigens which are used for nomenclature

• All three types undergo antigenic drift- minor changes in antigenicity due to mutations

• Infection predisposes to bacterial pneumonia

• Viral replication inhibited by rimantadine (amantadine). Can reduce disease severity if given within 2 days of onset

• Vaccination provides protection in 70% of individuals for about one year

• New vaccines produced each year dependent on the strains circulating in the previous year

PRION DISEASE *****

• Caused by host-encoded protein that is slightly altered in infected brain leading to accumulation in nerve cells

• Similar size to viruses, contain neither DNA nor RNA and replicate very slowly with a doubling time of over one week

• Resistant to heat, chemical agents and irradiation

• Cannot be cultured in vitro

• Do not induce an immune response  no antibody production

• Cause microscopic vacuoles in the brain giving a spongiform appearance

• Incubation period may be up to 20 years

• Transmissible by infected surgical instruments, tissue / organ transplantation and possibly vertically

• Cause Creutzfeldt-Jakob disease and Kuru in humans and BSE in cattle

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