Ecology and Evolution of Avian Influenza Viruses

This chapter discusses the ecology and evolution of avian influenza virus. Influenza A virus belongs to the family Orthomyxoviridae, a family of viruses with a negative sense, single-stranded, segmented RNA genome. This has been isolated from many host species including humans, pigs, horses, mink, cats, dogs, marine mammals, and a wide range of domestic birds. This influenza A virus genome consists of 8 gene segments. Wild birds form the reservoir for influenza A virus in nature, this transmits to other hosts which may cause serious disease. Virus transmission and geographical spread is thus dependent on the ecology of the migrating hosts. Classification of influenza A virus is genetic and antigenic variation of the surface glycoproteins HA and NA. Avian influenza A viruses can be classified based on their pathogenic phenotype in chickens, highly pathogenic avian influenza (HPAI) and all other avian influenza A virus subtypes are low pathogenic avian influenza (LPAI) viruses. These viruses are detected in gulls are LPAI viruses of subtypes H13 and H16 these appear to represent reservoir in nature. Domestic Birds are infected by HPAI Viruses mostly by direct contact with wild birds or indirect contact via human activities. HPAI H5N1 Virus in wild birds spread across a larger part of the world. LPAI viruses in wild birds vary with geographical location and continuous virus prevalence may be sufficient for the year-round perpetuation of viruses in these species without the need for environmental persistence.

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