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Pig Journal Volume: 69
Publication date: May 2013

General Section

Influenza pandemics: does the greater threat come from pigs, not birds?
K.Van Reeth

It is a central dogma in influenza virology, that pandemic influenza viruses come from wild aquatic birds. The classic viewpoint is that pigs are more susceptible to avian influenza viruses than people, and that they are essential intermediate hosts for the introduction of avian viruses or avian virus genes into the human population. The devastating outbreaks of ‘H5N1 bird flu’ in Asia in 2003 and the ensuing research, started to challenge many of the old theories about pigs and flu pandemics. Then, the first pandemic virus of this century did not come from birds, but it was a re-assortant of two well-established swine influenza viruses. The 2009, pandemic H1N1 virus is now a shared virus between humans and swine, and it continues to re-assort with endemic swine flu viruses worldwide. Some of these second generation re-assortants are also perceived as potential pandemic threats. It is reassuring though, that the human population will likely have partial immune protection against most of the H1 and H3 viruses that are endemic in swine, due to exposure to older human virus strains. Unlike other swine flu viruses, the 2009 pandemic H1N1 virus had the critical ability to spread efficiently from person to person. Researchers have tried hard to understand what makes this swine-origin virus so successful in humans. This paper discusses the major lessons from the complicated experimental studies with these viruses, as well as the caveats and difficulties. While it is impossible to make predictions about which animal influenza viruses may cause future pandemics, we can, for sure, improve our insights into the mechanisms of the species barrier. This requires: 1) pathogenesis and transmission studies with influenza viruses from various hosts in various domestic animal species, and 2) better surveillance for influenza in swine. Veterinary scientists can bring unique perspectives to this sort of research, and the success of surveillance relies very much on the co-operation of swine practitioners and producers. © Copyright The Pig Veterinary Society 2004


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