H5 subtype high pathogenicity avian influenza virus infections: current situation and countermeasures

Abstract

It has been 28 years since high pathogenicity avian influenza virus of the H5 subtype emerged in China in 1996. Owing to the failure of countermeasures at poultry farms in developing countries, viruses spilled into the environment. In addition, viruses were carried across continents by infected migratory waterfowl. Notably, viruses have been detected among wild birds in Japan during five consecutive winters since the winter of 2020–2021, and outbreaks have occurred continuously throughout each year in poultry farms. Such viruses have spread via migratory birds to Europe, Africa, and North America. Furthermore, infections have been reported in mammals, including foxes, that may have come in contact with infected birds. Given the viral history of the past few years, there is concern that not only low pathogenicity avian influenza viruses but also high pathogenicity avian influenza viruses are persistent in wild waterfowl populations. Continued intensive surveillance and control efforts among wild birds are required to prevent the transmission of viruses back into poultry and onward into wild mammals.