New World screwworm was confirmed in a Texas calf
The Canadian Food Inspection Agency (CFIA) is restricting some U.S. livestock imports following the detection of a deadly pest in the United States.
The CFIA made its announcement on June 5 after New World screwworm (NWS) was found in a Texas calf.
“Animals that originate from or were present in the State of Texas within 21 days prior to border crossing will not be accepted into Canada,” the CFIA said. “Taking this action now is an appropriate risk mitigation measure to prevent its introduction and protect animal health.”
The United States Department of Agriculture confirmed NWS on June 3. The affected animal is a three-week-old calf in Zavala County. That’s the first case of NWS in the U.S. since 1966.
Since the June 3 discovery, a calf in La Salle County, and a dog in Andrews County, have shown signs of NWS.
New World screwworms can’t survive Canadian winters, but they could cause damage during the summer months if allowed to enter the country.
NWS larvae eat living tissue of warm-blooded animals like livestock and pets.
These insects will target any open wound, but umbilical areas and horn buds of cattle are especially vulnerable.
As the NWS feeds, the wounds can get deeper and larger as more larvae hatch and feed.
A wound that worsens over time and is found with discharge or foul odour is a sign the pests are harming the animal.
Head shaking, scratching, severe irrigation, and isolation from the rest of the herd, can also be signs of NWS infestation.
NWS is also present in Mexico.
As a result, Canada has similar import restrictions on beef, pork, and other animals from Mexico.
In rare cases, NWS can infest people.
A June 2025 report indicated an 80-year-old Canadian who developed an ulcer on his right shin while in Costa Rica received treatment in Toronto.
Doctors removed two larvae from the ulcer, which were later tested and confirmed as NWS.
Top photo: New World screwworm larva (Dr. Heather Walden photo).