Born Free-Range

Via ProMED-mail: The Guardian reports on the ongoing bird flu debate over whether industrial poultry or wild birds are largely responsible for spreading the disease:

Grain's alternative theory for the emergence of H5N1 - which got backing in an editorial in the Lancet medical journal last month - starts with the observation that bird flu has coexisted pretty peacefully with wild birds, small-scale poultry farming and live markets for centuries without evolving into a more dangerous form of the disease. An explanation for this is that outdoor poultry flocks tend to be low-density, localised, and offer plenty of genetic diversity in breeding stock. By contrast, the hi-tech, intensive poultry farm, where as many as 40,000 birds can be kept in one shed and reared entirely indoors without ever seeing the light of day, is just like an overcrowded nursery of wheezy toddlers when the latest winter bug comes knocking - an ideal environment for spreading the disease and for encouraging the rapid mutation of a mild virus into a more pathogenic and highly transmissible strain, such as H5N1. "What we are saying is that H5N1 is a poultry virus killing wild birds, not the other way around," says Devlin Kuyek, from Grain.