Dog among 2 new Texas screwworm cases; Canada blocks Texas livestock imports

The U.S. Department of Agriculture (USDA) on Monday confirmed two additional cases of New World screwworm in Texas, widening a multi-agency response that has already triggered international trade restrictions.

Outbreak Widens with New Cases

What we know:

The latest cases involve a calf in La Salle County and a dog in Andrews County. According to the USDA’s Animal and Plant Health Inspection Service (APHIS), preliminary investigations indicate the infested dog had recently been in Mexico, where the parasite is known to be present. With these new detections, federal officials have now confronted four confirmed cases of the flesh-eating pest over the past week.

Canada imposes import ban

The announcement comes just as the Canadian Food Inspection Agency (CFIA) implemented emergency import restrictions on all livestock, including horses, entering Canada from Texas. 

Under the Canadian mandate, any animal that originated from or traveled through Texas within 21 days of reaching a border crossing will be denied entry to prevent the parasite from moving north during the warmer summer months.

About NWSW:

The New World screwworm is a destructive parasitic fly whose larvae burrow into the living tissue of warm-blooded animals, causing severe, often fatal wounds and significant economic losses for livestock producers. While it primarily threatens livestock, wildlife, and pets, it can in rare cases, infest humans. Officials emphasized that the U.S. food supply remains entirely safe, as the pest does not infest meat or agricultural products.

What they're saying:

"While we address these instances that require immediate attention... we are simultaneously working to eradicate the pest entirely," said Dudley Hoskins, Under Secretary for Marketing and Regulatory Programs. "We need the partnership of animal owners across the region – please stay vigilant, check your animals closely, and report anything that looks suspicious."

What's next:

In response to the growing outbreak, the USDA and the Texas Animal Health Commission (TAHC) have deployed an aggressive unified force of 75 ground personnel and hundreds of support staff nationwide. Authorities are establishing 20-kilometer (12-mile) quarantine and movement-control zones around the confirmed detections, increasing trapping along the Mexican border, and conducting wildlife surveillance.

Sterile fly release

To halt the pest's reproduction cycle, the USDA has activated a sterile fly dispersal facility at Moore Air Base in Edinburg, Texas. Aerial dispersal flights are scheduled to begin Tuesday to release millions of sterile flies over the infested areas. The sterile insects are dyed with a fluorescent green or orange marker that glows under UV light, allowing animal health officials to easily distinguish them from wild, fertile flies if captured in monitoring traps.

In Canada, the New World screwworm is classified as an immediately notifiable disease under the Health of Animals Act, requiring laboratories to report any suspected cases immediately.

Both U.S. and Canadian authorities are urging livestock owners, veterinarians, and pet travelers to rigorously inspect animals for draining or enlarging wounds, visible maggots, or unusual discharge. Any suspected infestations in the U.S. should be reported immediately to state animal health officials or the USDA.

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