Until now, the most accepted theory for the spread of any kind of bird flu involves migratory birds carrying the disease. Though the potential still exists for this to happen, scientists predicting a pandemic spread in this manner are back-peddling just a bit. Wild birds have begun to migrate from the Asian continent, where the disease was first discovered, but there has yet to be an outbreak affecting large numbers of domesticated birds.
Closer to home, scientists believe the lack of sick birds or humans in North America might be attributed to production practices. Most of the fowl raised for human consumption in the U.S. and Canada is reared indoors. This common method of animal management may be responsible for blocking exposure to disease carrying migratory birds.
Because the disease is not spreading as predicted some attention is turning to domestic live-birds exported from Asia. At this point, no bird flu outbreaks have been attributed to domesticated birds handled in this way.
Despite the fact that a mutation has not occurred allowing human-to-human transference of the disease, or an explanation of why larger outbreaks of bird flu have not been found, health officials are not discarding any theories. Right now, the scientific and medical communities remain cautious.
Since 2003, more than half of the 120 human related bird flu cases caused by the H5N1 virus, all of them in Asia, have resulted in death.