Zoonotic influenza

Zoonotic influenza refers to disease caused by animal influenza viruses that cross the animal–human divide to infect people. People can be infected with influenza viruses that are usually circulating in animals, such as avian influenza virus subtypes A(H5N1) and A(H9N2) and swine influenza virus subtypes A(H1N1) and (H3N2). Other species including horses and dogs also have their own varieties of influenza viruses. Even though these viruses may be named as the same subtype as viruses found in humans, all of these animal viruses are distinct from human influenza viruses and do not easily transmit between humans.  

Some zoonotic influenza viruses may occasionally infect humans, and can cause diseases in people ranging from mild conjunctivitis to severe pneumonia and death. Usually these human infections of zoonotic influenza are acquired through direct contact with infected animals or contaminated environments, and do not spread quickly between people.  

If such a virus acquired the capacity to spread sustainably from one person to another, it could start a pandemic because it would be so new that humans would have little immunity to it. Over the past decades, there have been multiple instances of sporadic transmission of influenza viruses between animals and humans.  

When animal influenza viruses infect their natural animal host, they are named for that host, as in avian influenza viruses, swine influenza viruses, equine influenza viruses, etc. As such, the term “swine flu” refers to swine influenza viruses infecting swine. Disease names should not refer to geographic locations.