New research argues that birds are not the source of the 2009 H1N1 outbreak or the 1918 pandemic.
Scientists from the Canadian Food Inspection Agency's National Centre for Foreign Animal Disease (NCFAD) in Winnipeg, Canada, together with collaborators in the USA, injected the 2009 and 1918 H1N1 virus strains individually into chickens. None developed flu symptoms or showed any signs of tissue damage up to18 days later, although about half the chickens developed antibodies against the 1918 H1N1 virus showing limited infection. The 1918 H1N1 virus also did not cause disease in ducks. The origin of the 1918 H1N1 virus is unknown and despite its genetic similarity to avian influenzas, the results of this study show it is unlikely to have jumped the species barrier from chickens to humans.The result is that culls and quarantines are unlikely to be helpful for stopping the spread of those two viruses.
Different strains of influenza cause disease in humans, birds and pigs; each type of virus is adapted to cause infection in its host. All cause similar respiratory symptoms. If flu viruses are passed back and forth between hosts (e.g. through close human contact with infected animals) the mixing can lead to development of a novel strain. As they have not encountered the virus before, the human population has little or no immunity to a novel strain which can easily cause infection and spread from person to person. This may ultimately lead to a global flu pandemic.