Bird flu is hitting the U.S. hard. Now, migratory birds are flying north

Bird flu is at a dangerous point in the United States: Nearly 167 million birds have been impacted by the H5N1 strain since 2022, and 70 people have been infected. Now, birds are flying our way for the spring migration season.

A snow goose near Montreal, a great horned owl in southwestern Ontario, a Canada goose in Langley, B.C. — these are just some of the wild birds that have recently tested positive for H5N1 in Canada. But scientists are bracing for more, and are ramping up their efforts to monitor and curb the virus this season.

This winter has seen more outbreaks of H5N1 than usual, said Dr. Manon Racicot, a veterinary epidemiologist with the Canadian Food Inspection Agency (CFIA) in Saint-Hyacinthe, Que.

"Now that the birds are coming back north for the migration, we don't really know what's coming to us. Will the birds still be infected? Will they be shedding the virus in the environment in Canada?"

Adding to scientists' concern: Another strain of bird flu, H7N9, has been reported in a poultry farm in Mississippi, U.S. — a first since 2017. While it's not the dominant type of bird flu currently making the rounds in the U.S., H7N9 has a far higher death rate than H5N1, killing nearly 40 per cent of humans infected since it was detected in 2013. The infected birds have been killed, and the premises quarantined, said state authorities.

H5N1 has also crossed species, and adapted to mammalian hosts. Animals like seals, cats and dogs have died after mingling with wild birds, or eating raw pet food. 

Dairy cows in the U.S. have been getting sick in droves, with 989 herds affected across 17 states, according to the Centers for Disease Control and Prevention.

Bird flu does not appear to be easily transmissible between people, for now. But the strain of H5N1 circulating in cows in the U.S. is just one mutation away from being more transmissible between humans, suggests a study recently published in the peer-reviewed journal Science. 

And when it infects humans, the virus can be deadly. In January, a senior in Louisiana became the first H5N1-related human death in the U.S.

Canada's only known case of H5N1 was confirmed two months earlier, in November: a teenager in British Columbia who was hospitalized for two months. We still don't know how she was infected.

In both cases, genetic analysis suggested the virus had mutated to become more effective at attaching to cells in the upper respiratory tract. 

All this has scientists and physicians on high alert. 

"Quite frankly, a single case of avian influenza is very concerning because we do not want that virus to adapt to humans," said Dr. Danuta Skowronski, an epidemiologist at the B.C. Centre for Disease Control (BCCDC).

"We all have a responsibility to shut that down as rapidly as possible to contain it. That's a global effort. We are communicating globally with the U.S., with the U.K., with wherever we can to ensure we get the best possible knowledge."