Avian flu research, conceptual computer artwork. Researchers are trying to develop treatments and vaccines to avian flu before it can mutate into a form that can spread between humans, which could cause millions of deaths worldwide. The H5N1 strain of the avian influenza virus first appeared in humans in 1997, and killed 60 people between 2003 and 2005. It is contracted through close proximity to infected birds. Wildfowl are the natural carriers, and are rarely affected by the disease, but it can spread to poultry, in which it is fatal. It cannot be contracted by eating chicken meat or eggs.