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Bird Flu
Bird flu is an infectious disease of birds and humans caused by various
subtypes of Influenza A. There are 3 antigenic types of Influenza virus: A, B and C. Influenza A
occurs in humans as well as in a number of animal species such as wild birds, pigs, ducks, hens,
turkeys, horses and cats. Influenza B viruses circulate only among humans, they are not divided
into subtypes and they are not subject to any antigenic changes. Influenza A virus is subject to
small changes that happen continually over time, called “antigenic drifts". The division of
Influenza A virus into subtypes is based on 2 proteins that can be found on its surface, the
hemagglutinin (H) and the neuraminidase (N). To date, 15 subtypes of H (H1-H15) and 9 subtypes of N
(N1-N9) have been found. H5, H7 and H9 subtypes are responsible for infection both in humans and
birds and they are characterised by "high pathogenicity”. The latter (H9) are more infectious to
birds, horses, pigs and cats than humans. Influenza strains are neutralised in 56º C and cease to
be pathogenic. Since 1997, the main virus strains that began to infect humans are H9N2, H7N7 and
H5N1. Influenza virus is released in high concentrations through feces and it can be long-lived,
especially when found in low temperature water.
A.
Prevalence and geographical distribution
B.
Ways of Transmission
C.
Incubation Period
D.
Symptoms
E.
Protective measures
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