After millions of years of existing as a harmless infection of aquatic birds, some strains of avian flu have developed the ability to mutate into highly pathogenic forms that may not only be deadly for birds, but potentially more dangerous for humans as well. Experts from the World Health Organization, the World Organization for Animal Health, and the Food and Agriculture Organization of the United Nations have joined leading scientists in implicating industrialized poultry production for providing fertile ground for the transformation of benign bird flu into highly pathogenic strains.
Live bird markets can be the conduit by which waterfowl viruses enter into industrial poultry populations and have been identified as playing a critical role in the emergence of H5N1, a deadly strain of avian influenza threatening to trigger a human flu pandemic. In response, Asian countries are shutting them down. In the United States, live bird markets have been tied to domestic outbreaks of highly pathogenic avian influenza and have been described by U.S. Department of Agriculture poultry researchers as the “missing link in the epidemiology of avian influenza,”1 yet hundreds of these retail storefront slaughter markets still operate across the country, processing tens of millions of birds annually.
The Humane Society of the United States, "An HSUS Report: Human Health Implications of U.S. Live Bird Markets in the Spread of Avian Influenza" (2007). ENVIRONMENT AND HUMAN HEALTH. 9.