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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