Via CMAJ: World watching as troubling new type of avian influenza surfaces in China. This is a concise account of the situation so far, with Canadian experts' comments, and a Canadian angle in this excerpt:
H7- and H5-group influenza viruses have characteristics that are of particular concern in birds. "It is known in the scientific community that H7 and H5 viruses are prone to mutate," explains Dr. Abed Harchaoui, senior staff veterinarian in the Foreign Animal Disease Section of the Canadian Food Inspection Agency.
H7 and H5 subtypes normally circulate in wild birds and may be transmitted to domestic poultry such as chickens and turkeys in several ways. "It can be contact between wild birds and poultry through free-range farming," explains Harchaoui, "Also from excretion from the birds from outside to inside of the barn. People can step in it and get it on their boots."
"In some situations, like ducks and geese, the virus is low pathogenic, but might mutate very quickly in chickens and turkeys," becoming highly pathogenic and causing severe symptoms and death.
This was demonstrated dramatically in an outbreak of a related influenza, H7N3, in a chicken farm in the Fraser Valley of British Columbia in 2004. The virus had caused only decreased egg production and a slight uptick in mortality in a barn on the farm. But an outbreak 10 weeks later in a second barn caused a spike in mortality, because of a genetic mutation occurring between one barn and the other (Rev Sci Tech 2009;28:349-358).
