Avian flu: Catch up on spread, risks, and guidance from health experts

After another case of H5N1 avian flu linked to dairy cows was confirmed in a second dairy farmer in the United States, some Canadian experts say the federal government needs to expand surveillance of the virus north of the border.

"We need to expand, in my opinion, to conducting serological surveillance, which means looking for antibodies that might suggest a past exposure either in dairy workers or in cattle," said Angela Rasmussen, a virologist with the University of Saskatchewan's Vaccine and Infectious Disease Organization.

"We need to continue to work with our colleagues in the U.S. as well to make sure that we are targeting surveillance appropriately," she added.

The virus has spread widely among cattle in the United States and as of Wednesday H5N1 has been confirmed in 51 dairy herds in nine states, according to the U.S. Agriculture Department.

Surveillance south of the border has ramped up to include monitoring people exposed to infected animals,  wastewater testing and enhanced nationwide summer monitoring of the virus. 

Should we be worried?

"The risk to the general public right now is low," said Dr. Isaac Bogoch, Infectious disease specialist at the Toronto General Hospital.

"The concern, of course, is that if this virus has some additional mutations that make it more readily transmissible between mammals, it would be problematic."

The Canadian Food Inspection Agency is testing for viral fragments in milk sold on store shelves, requiring negative test results for lactating dairy cows imported from the United States and facilitating the voluntary testing of asymptomatic cattle. 

As of May 16, The Canadian Food Inspection Agency has tested 303 samples of retail milk. It says all 303 tested negative for H5N1.

Wastewater testing isn't currently part of the federal government's surveillance plan.

One researcher from the Canadian Research Institute for Food Safety at the University of Guelph says his team has developed methods to test wastewater for a variety of different pathogens. In the last couple of months, researchers started testing for H5N1.

"We did not have robust surveillance programs in place during that pandemic. So those programs were subsequently developed such as wastewater-based surveillance," said Lawrence Goodridge.

"We would not be able to say that it came from humans or cattle or any other source. But what it does tell us is that it's in the environment. And so that can then allow us to begin to take precautions to stop it's spread,"

There are no reports yet of any bird flu cases in humans or cattle in Canada, but H5N1 has infected tens of millions of birds including poultry on various farms in the country.

"We’re monitoring the situation very closely," said Federal Health Minister Mark Holland. "Not just in the human population, but obviously in the bovine and broader mammalian population."

FILE: Eggs are cleaned and disinfected at a plant in California on Jan. 11, 2024. (Terry Chea / The Canadian Press)

Who has been exposed?

A dairy farm worker in Texas was the first person to contract the bird flu linked to dairy cows. The second person to get infected is also a dairy farmer. U.S. Centers for Disease Control and Prevention officials said both patients recovered and had mild symptoms including conjunctivitis.

"This particular second case in Michigan is very interesting to me because it is similar to the case in Texas in that it wasn't associated with any kind of respiratory disease," said Rasmussen.

"We don't know that for sure, but the current working hypothesis is that people in dairy farms may be exposed directly to milk rather than exposed to aerosols in the air."

The CFIA has confirmed that milk and milk products sold in Canada are safe because they've been pasteurized, which is a process that kills harmful pathogens. The agency says no evidence eating well-cooked beef can transmit bird flu to humans and that all evidence indicates that careful cooking will kill the virus.

The Centre for Disease Control (CDC) in the United States recommends checking the internal temperature of meat while cooking it. Bringing food to an adequate temperature ensures the food is cooked through to the point of minimizing your risk of ingesting viruses.

• Poultry and eggs: 74 C (165 F) 
• beef, veal, lamb, and pork, including fresh ham: 63 C (145 F) (then allow the meat to rest for 3 minutes before carving or eating)
• Ground meats, such as beef and pork: 72 C (160 F)

The World Health Organization says bird flu has killed about half the nearly 900 people it has infected worldwide over the past two decades.