Bird flu in cattle: What are the concerns surrounding the newly emerging bovine H5N1 influenza virus?

By Nitish Boodhoo, University of Guelph

The confirmed presence of bird flu in American dairy cattle in a March 25 report from the U.S. Department of Agriculture (USDA) — and a case in Texas where a human working with cattle was infected — has put Canadian public health experts on high alert.

But, what is bird flu and what do we know about influenza in both poultry and cattle?

Bird flu, also called avian flu, refers to infection caused by the avian influenza Type A viruses. In the wild, influenza viruses generally spread among migratory waterfowls, such as ducks and geese. Within avian species, domestic poultry are highly susceptible to infection with Type A avian influenza viruses, including H5N1.

Canada itself is amid an H5N1 avian influenza virus outbreak, with over 11 million domestic poultry estimated to be affected and culled to date. In fact, a major concern for the Canadian poultry supply chain is the incurred financial loss from culling birds.

This virus is highly contagious among domestic poultry and can spread through an entire flock within a matter of days. The most common route of transmission from an infected bird to a non-vaccinated bird is via direct physical contact or contact with virus-contaminated surfaces with bodily fluids such as oral mucus and feces.

Bird flu in mammals

Non-avian species, like mammals, can also become infected with the H5N1 virus. In Canada, sporadic cases of mammals becoming infected with bird flu have been reported in raccoons, striped skunks, red foxes, cats and dogs.

As of March 2024, various reports from the USDA, Food and Drug Administration, and Centers for Disease Control and Prevention (CDC) confirmed the presence of H5N1 in dairy cattle across eight states, of which Idaho, Ohio and Michigan are the most northern states bordering Canada.

Although there are no known reports indicating the current bovine strain has made its way into Canada, there is no doubt that it is getting too close for comfort.

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