Back where virus started, new scrutiny of pig farming

Despite the buttoned-up methods of farmers such as Schott, many experts think pig farming presents a serious and overlooked risk to public health. Proof of that assertion -- indirect but indisputable, in the opinion of virologists -- is the 2009 H1N1 pandemic influenza. Little is known about the origin of the novel H1N1. But one thing is virtually certain: The bug now infecting the people of more than 190 countries began in a pig. Detecting such cross-species transfers quickly -- or, better yet, preventing them -- is an urgent priority in a field that has spent most of its energy in recent years worrying about the emergence of flu from birds in Asia. A major concern now is what might happen if the pandemic H1N1 virus spreads widely in pigs, and then out again into the human population. What worries virologists is the mixing of human and swine flu strains -- or, worse, human, swine and bird strains. That can lead to "reassortment," in which strands of genetic material are exchanged to yield a new virus, often with behavior not seen in its parents. Those features can include higher contagiousness, rapid growth, the ability to infect the lungs and, most important, an unfamiliar appearance to the immune system. Reassortment is rare, and it is even rarer when the product is a strain that can spread like wildfire. That is one reason influenza pandemics occur only a few times a century. (The last one was in 1968.)...read more