Epidemiology and Pathogenesis of Avian Influenza Type a Virus Infection in Poultry, A Review

Avian influenza (Bird flu) is a highly infectious disease caused by an Orthomyxovirus of the family Orthomyxoviridae. Avian influenza viruses are classified in the genus influenza virus A that infects wide variety of domestic and wild animal species. Aquatic birds are the natural hosts of avian influenza viruses as asymptomatic carriers. Mode of transmission of this virus in poultry flock is through ingestion, inhalation and mechanical transmissions and its clinical signs are variable. Avian influenza is distributed worldwide. According to disease severity avian influenza is classified into two forms: highly pathogenic avian influenza (HPAI) also known as fowl plague, and low pathogenic avian influenza (LPAI). HPAI viruses are highly virulent representing the greatest concern for public health and economic importance and categorized as List a disease by OIE. Diagnosis mainly depends on isolation and identification of viruses. Serological tests and RT-PCR are also used. The disease is not treatable except trials for secondary microbial complications. Biosecurity is the most useful method for prevention and control.