Highly Pathogenic and Low Pathogenic Avian Influenza A Viruses
Avian influenza A viruses are designated as highly pathogenic avian influenza (HPAI) or low pathogenicity avian influenza (LPAI) based on molecular characteristics of the virus and the ability of the virus to cause disease and mortality in chickens in a laboratory setting.
Infection of poultry with low pathogenic avian influenza A (LPAI) viruses may cause no disease or mild illness (such as ruffled feathers and a drop in egg production) and may not be detected. Infection of poultry with highly pathogenic avian influenza A (HPAI) viruses can cause severe disease with high mortality. Both HPAI and LPAI viruses can spread rapidly through poultry flocks. HPAI virus infection can cause disease that affects multiple internal organs with mortality up to 90-100% in chickens, often within 48 hours. However, ducks can be infected without any signs of illness. There are genetic and antigenic differences between the influenza A virus subtypes that typically infect only birds and those that can infect birds and people.