Canadian milk should be tested for H5N1: animal health expert

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Canada should start testing milk to determine whether Canadian dairy cattle are infected with the H5N1 bird flu virus strain that is spreading through cattle in the U.S., says director of the Center for Public Health and Ontario Veterinary College Zoonoses.

Despite assurances from government officials that no cases of highly pathogenic avian influenza (H5N1) have been identified in Canada, J. Scott Weese, who is also a professor at the Ontario Veterinary College and an infectious disease specialist, said no there has been enough surveillance to say with certainty that he is not in Canada.

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“We don’t know if we have it in this country in cattle. We don’t have testing yet, but we haven’t done much surveillance,” Weese said.

Given the spread of the virus among livestock in the U.S., Weese said, Canada needs to implement more active surveillance to understand if and to what extent it is also found in Canadian livestock.

The Canadian Food Inspection Agency recently said on X, formerly Twitter, that it is not testing raw or pasteurized milk, as was done in the U.S., because the virus has not been identified in Canadian cattle. The CFIA also said H5N1 is not a food safety issue since pasteurization kills any viruses in milk.

In the United States, inactive fragments of the H5N1 virus have been found in about 20 percent of retail pasteurized milk samples tested by the Food and Drug Administration. Inactive fragments have also been found in cottage cheese and sour cream. The meat was also analyzed, but no virus fragments were identified.

Those findings suggest that H5N1 is more widely spread among dairy herds than previously reported. To date, the H5N1 virus has been confirmed in at least 36 dairy herds in the United States, a dozen of them in Texas. But the amount of inactive virus found in the milk suggests broader asymptomatic spread, meaning the cows would not be identified as sick.

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Weese said having a clearer understanding of the Canadian livestock situation would make it easier to control the spread in Canada and even eradicate it by managing sick animals if it were found.

“A little more clarity would be nice.”

Currently, the Canadian Food Inspection Agency supports testing if a farmer identifies a problem.

“We are in the passive surveillance stage, waiting for reports to arrive through the usual channels. Active surveillance is generally better when you know what is going on.”

And Weese said there should be more transparency about what the response is if a positive animal is identified. In the case of bird flu in poultry, entire flocks have been culled, which is not the case with cattle, but there could be restrictions on the movement of animals and the sale of milk.

Both animal and human health officials say the risk to humans remains low. One human case has been identified in the US related to current outbreaks of avian influenza in livestock. There have been anecdotal reports of other cases of illness among people working on farms that were not formally reported.

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The Canadian border has not been closed to imports of livestock from the United States, he said, but restrictions have been put in place to prevent infected animals from entering Canada. Weese said it is more common for Canadian cattle to go to the United States to be slaughtered than the other way around.

Although the current risk to humans is low, Weese said the more it spreads in domestic mammals with close contact with humans, the greater the chance that the virus will change and become a greater threat to humans, which is why which requires more vigilance and a clearer understanding of the situation is important.

Still, he said, “we are not at the point of saying that this has a great chance of becoming a pandemic virus.”

However, testing milk sold in Canada is an easy task to better understand the situation and take measures to contain it, if necessary.

“You can’t control it if you don’t look.”

Pasteurized milk, even with inactive fragments of the virus, does not pose a risk to human health, but raw milk could and is considered high risk for other reasons. The sale of raw milk is prohibited in Canada, although a small number of people sell and consume it.

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