As the H5N1 avian influenza virus continues to spread among poultry and cattle in the United States — and has infected a dairy worker in Texas — public health and infectious diseases experts in Canada are eagerly awaiting the latest surveillance updates to better understand the risks across North America.

On May 3, Canadian health and food agencies announced efforts to step up testing and surveillance in Canadian cattle and milk. So far, the highly pathogenic avian influenza hasn’t been detected among dairy cows or commercial milk, and the Canadian Food Inspection Agency reported that the virus isn’t a food safety concern in pasteurized milk or fully cooked poultry and eggs.

“We’re in an unknown period. Since it’s apparent that H5N1 was likely in US cattle for a few months before it was recognized (and before any controls were placed on cow movement), we have to have some degree of concern that it’s here,” Scott Weese, DVM, professor of pathobiology at the Ontario Veterinary College and director of the University of Guelph’s Centre for Public Health and Zoonoses, Guelph, Ontario, Canada, told Medscape Medical News.

“We have no evidence of that, as far as I know, but we have to do some looking and take some more time to figure out whether it’s truly made it here or not, he said.

Virus Surveillance Status

As of May 14, the Centers for Disease Control and Prevention (CDC) in the United States had identified H5N1 in 46 dairy herds across nine states, including new cases reported in Colorado, Idaho, and Michigan on May 7 and 8. In a recent paper, Iowa State University, Ames, Iowa, researchers confirmed that several domestic cats became sick and died in March after drinking raw milk from sick cows on a north Texas dairy farm. In a preprint paper, researchers from California and Georgia detected increases in the virus at 59 wastewater treatment plants across the country.

The CDC also announced on May 8 that current flu surveillance systems can detect transmission and early changes in the H5N1 virus, noting that the “current risk to the general public remains low.” People with close or long exposure to infected birds or livestock, however, face greater risks and should be monitored for signs of respiratory illness, the agency said.

“We still have only partial information from the United States. The US Department of Agriculture has started to communicate more, but there are major testing gaps,” said Weese. “On-farm surveillance seems limited, in large part because of reluctance of farms to allow people on the farm to test. In Canada, the recent announcement that surveillance will be started was great to hear.”

The Canadian Food Inspection Agency (CFIA), Health Canada, and Public Health Agency of Canada launched a program to monitor samples of milk collected at the retail level. CFIA laboratories will test the milk samples using polymerase chain reaction tests, and the first round of results is expected to be available by mid-May, the agency told Medscape Medical News. The results will be shared publicly and available on the CFIA website.

“There is currently no evidence to suggest that food, including milk and meat, can transmit avian influenza to humans,” the CFIA media team told Medscape Medical News. “Canada has strong food safety regulations in place to protect the Canadian food supply.”

Canadian agencies announced changes to require negative test results for lactating dairy cattle being imported from the United States, as well as voluntary testing of cows that don’t have clinical signs of the virus. The CFIA is also expanding its current guidance for private veterinarians for the collection and submission of samples for voluntary testing of cows. The updates will be “available in coming days,” the agency told Medscape Medical News.

“I hope we’re taking a proactive approach — if we wait and see, we’ll always be left behind,” Isaac Bogoch, MD, associate professor of medicine at the University of Toronto and infectious diseases expert with the University Health Network, Toronto, Ontario, Canada, told Medscape Medical News.

“With any outbreak response, transparency and data sharing are important, as well as working with any groups that are impacted, such as building trust with the farming community,” he said. “For instance, what are the different incentives for screening cattle, and what might the economic impact be if there’s a positive test? We have to think about the compensation and incentives for farms to participate in screening.”

Potential Human Health Risks

The growing burden of H5N1 infection in mammals has put public health experts on alert, Bogoch said, particularly since infectious diseases specialists have monitored it for years after it was identified in geese in China in 1996 and infected 18 people in Hong Kong in 1997.

“H5N1 has been known to be an infection of pandemic potential for over 25 years,” he said. “This is the prototype virus that people who work in emerging and reemerging infectious diseases have been looking at for decades, and when you see more of the virus around and it’s doing things it wasn’t doing before, it raises a red flag to say we should get on this.”

For now, though, most infectious diseases and animal health experts aren’t directly concerned about this flu strain causing human-to-human spread, Weese said, because it’s not well adapted for humans. Instead, they’re more focused on the potential of having more flu viruses in circulation.

“The more circulation and the more species that are involved, the greater the chance for more adaptation and recombination with other flu viruses,” he said. “Whether it’s cattle, cats, or other species, we don’t want novel flu strains in circulation, especially in domestic animals that we have contact with.”

The Texas dairy worker who became infected, for instance, contracted a slightly different flu strain than the one identified in US cattle outbreaks, which raises questions about virus mutation, mammal-to-mammal spread, and mammal-to-human adaptation, said Allison McGeer, MD, professor of laboratory medicine and pathobiology at the University of Toronto and an infectious diseases specialist with the Sinai Health System, Toronto, Ontario, Canada.

“We’ll see in the next couple of weeks what the surveillance shows here,” she said. “It’s a good thing for those of us in Canada that the US has identified this and is moving on it as quickly as possible, and we’ll keep our fingers and toes crossed that it hasn’t crossed the border.”

In the meantime, the experts recommended thinking about human testing. In Canada, for instance, combined viral testing kits can pick up COVID-19, flu strains, and respiratory syncytial virus, McGeer noted, but additional testing would be needed to identify the specific H5N1 proteins. In addition, patients who are sick may not come forward for testing or feel sick enough to visit a doctor.

“The human surveillance aspect is OK but not brilliant, and that’s what everybody in every jurisdiction seems to be feeling,” she said. “We’re watching, and adding to the current efforts takes time, energy, and resources, so it’s hard to judge right now what to do and how quickly and how far to move.”

That’s why it’s so important to monitor wastewater samples and asymptomatic cattle while waiting on preliminary results in Canada, she added.

“Then we need to brace ourselves and think about the next steps, depending on what we find,” McGeer said. “Outbreak control measures can be expensive and difficult, so we need to think about how to support the dairy industry and make sure they’re getting through this as safely and effectively as possible.”