Influenza viruses circulating in animals pose threats to human health. Humans can be exposed to these viruses, such as avian influenza virus subtypes H5N1 and H9N2 and swine influenza virus subtypes H1N1 and H3N2, in many ways, such as:
- when people's work brings them in contact with infected animals.
- when people contact infected animals during their everyday lives, such as when visiting live animal markets or when these animals are kept as part of the household.
- when people handle or slaughter infected animals, or work with raw meat and by-products from infected animals.
- when people contact things around them, such as animal housing areas and equipment, ponds and other water sources, faeces, and feathers, if these things are contaminated with influenza viruses.
In some cases these zoonotic infections (infections in humans acquired from an animal source) result in severe disease or even death in humans, but often these infections result in only a mild illness or appear to cause no illness at all. All human infections with animal influenza viruses are of concern, not only because of the cases of disease and deaths in individual people, but also because if these viruses become able to spread from human to human they could spark a pandemic. All of the past four pandemic influenza viruses have contained gene components originating in animals.
The actual public health risks posed by influenza viruses circulating in bird, swine, and other animal populations are not completely understood. Recent findings suggest that influenza viruses in animals and humans increasingly behave like a pool of genes circulating among multiple hosts, and that the potential exists for novel influenza viruses to be generated in swine and other animals. This situation reinforces the need for close monitoring and close collaboration between public health and veterinary authorities. WHO continues to work vigilantly with national ministries of health and animal health sector partners globally to identify and mitigate these influenza public health risks at the human-animal interface.