The typical story is that wild migratory birds carried the flu from China. A new article challenges this view, claiming that "the timing and distribution of the reported spread of H5N1 ... does not fit any known migratory pattern for any species". The alternative theory:
The article argues instead that the disease was more likely spread by the unrestricted movement of domesticated poultry, or even illegal trade in fighting cocks.
This view is also supported by research by Dennis Alexander in the journal Veterinary Microbiology. He argues that although wild birds may carry many types of flu and may infect agricultural birds, it is human movement of birds through farming, slaughter and trade that accelerates its spread.
Read the entire controversial piece here.