Researchers continue to work on other types of bird flu vaccines.
HPAI and LPAI designations do not refer to the severity of illness in cases of human infection with these viruses; both LPAI and HPAI viruses have caused severe illness in humans Poultry infected with LPAI viruses may show no signs of disease or only exhibit mild illness such as ruffled feathers and a drop in egg production which may not be detected.
Top of Page 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.
Only two influenza A virus subtypes i. Although there are several types of bird flu, H5N1 was the first avian influenza virus to infect humans. Recent data showed seals also can be infected. Slaughtering, defeathering, handling carcasses of infected poultry, and preparing poultry for consumption, especially in household settings, are also likely to be risk factors.
Subtypes of Influenza A Viruses Influenza A viruses are divided into subtypes on the basis of two proteins on the surface of the virus: hemagglutinin HA and neuraminidase NA. The first infection occurred in Hong Kong in In the past, programs that have focused on singular, place-based understandings of disease transmission have been ineffective.
There are 18 known HA subtypes and 11 known NA subtypes.