The Canadian Food Inspection Agency (CFIA) announced on Friday that it would temporarily restrict livestock from entering Canada from affected parts of the United States, after screwworm, a flesh-eating parasite, was detected in a calf in Texas.

Animals, including horses, that have been in Texas within the past 21 days will not be allowed to cross the Canadian border, the CFIA said in a news release.

The move comes after U.S. officials on Wednesday announced that New World screwworm had been found in Texas — the first such case in the United States since the 1960s.

Endemic to South America and the Caribbean, the flesh-eating larvae of this parasitic fly burrow into skin to feed on living tissue of an animal host, which can — on rare occasions — include humans.

A highly successful eradication program wiped out screwworm from North and Central America by the mid 2000s. But since 2024 an outbreak of the parasite has spread among livestock in Mexico.

Several U.S. states are also taking precautionary measures to limit the risk of spread, the CFIA noted, adding it was working closely with American officials. 

While the parasite is unlikely to become established in Canada, the CFIA urged animal owners to remain vigilant.

"While our colder climate is not hospitable for the long-term establishment of the fly in Canada, they can survive shorter periods of time in the summer months," it wrote.

"Animal owners and veterinarians are encouraged to be on the lookout for signs of screwworm infestations in livestock. A wound that worsens over time and is accompanied by discharge or foul odour is also usually observed."

New World screwworm is an immediately notifiable disease under the Health of Animals Act, meaning that owners should contact a veterinarian if they suspect an infestation. Identification can only be confirmed by a laboratory, which would then be required to notify the CFIA.