close
close

Canada will test milk for H5N1 bird flu after harmless traces found in American cattle

Canadian food safety and agriculture officials will test retail milk for harmless traces of the bird flu virus as they step up efforts to determine whether a highly pathogenic version of H5N1 has spread undetected to Canadian livestock from herds in the United States States.

The Canadian Food Inspection Agency announced Friday that it would also facilitate voluntary testing of apparently healthy cows for bird flu. The statement provided no details on how they would do that.

Earlier this week, the agency said in a notice to Canada’s dairy industry that lactating cows could no longer be imported from the U.S. without proof of negative flu tests. That change came into effect on April 29.

H5N1 has not yet been found in cows in Canada, but some doctors and scientists worry that cases have been missed because officials waited for farmers and field veterinarians to report symptoms in cattle, rather than actively looking for the virus.

The U.S. Department of Agriculture announced on March 25 that it had confirmed cases of highly pathogenic bird flu in cows in Texas and Kansas for the first time. The virus has now been found in 36 herds of dairy cattle in nine states, including the border state of Michigan.

The finding of bird flu in cows raises alarm bells because of the threat the virus could pose to livestock, and because wider transmission among mammals could give the virus more opportunities to evolve into a human-to-human pathogen.

For now, however, public health officials say the risk to humans is very low unless they work directly with farmed or wild birds. USDA testing of samples of milk and milk products, such as sour cream and cottage cheese, has shown them to be safe due to pasteurization, the process of heating milk to kill pathogens.

However, USDA testing found harmless virus fragments in one in five retail milk samples tested in April — an indication that bird flu may be more widespread among cows than currently known. Testing of retail milk in Canada could serve the same surveillance purpose.

The USDA also said this week that testing of ground beef from states with infected herds found no trace of the virus.

Since 2003, nearly 900 human cases of bird flu have been confirmed in 23 countries. Just over half were fatal, but the actual death rate is likely lower because only the sickest patients come to the attention of authorities.

“We have obviously paid a lot of attention to H5N1 since its first identification in 1996, and it has not yet acquired a series of mutations and mechanisms that would allow it to easily replicate in the human respiratory tract and spread from one person to another .” said Greg Rose, an infectious disease and infection control consultant at Queensway-Carleton Hospital in Ottawa.

Dr. However, Rose said the risk of this is decreasing as a highly pathogenic version of the virus, known as H5N1 2.3.4.4b, travels around the world, wiping out populations of poultry and wild birds and infecting more species of mammals, including raccoons, skunks, red foxes , cats, dogs, sea lions and dolphins.

More than 11 million farmed birds have died or been culled since the virus was first detected in Canada in December 2021.

So far, H5N1 2.3.4.4b causes a relatively mild disease in cows, characterized by loss of appetite, a steep drop in milk production, lethargy and fever. As far as we know, no cows have died from the virus.

The only confirmed human case linked to the outbreaks was found in a Texas farm worker whose only symptom was pink eye.

A new report published Friday in the New England Journal of Medicine suggested that the worker may be the first discovered example of bird flu transmission from a mammal to a human. People who have been infected with the virus in the past have had direct contact with sick birds. The Texas worker did not do that, according to the report, written by scientists from the Centers for Disease Control and Prevention and the Texas Department of State Health Services.