Another cause for concern: flu season is underway in the U.S., and as seasonal influenza virus goes around, “humans, ourselves, could be a mixing vessel,” Davis says. If a person were simultaneously infected with bird flu and seasonal flu, the two viruses could theoretically combine to create a more transmissible strain.

Canadian health officials have confirmed bird flu in a British Columbia teen. The Public Health Agency of Canada said Wednesday that tests showed the virus involved was related to a bird flu outbreak in poultry in the province.

British Columbia health officials have yet to identify a likely source of the infection, though none of the teen's contacts have tested positive for the virus so far.