Texas is at the center of a growing agricultural emergency after the discovery of flesh-eating screwworm parasites in two calves prompted Canada to ban cattle imports from the state, marking the first confirmed U.S. cases of the pest in roughly six decades.
Why It Matters
The screwworm outbreak poses a direct threat to the Texas cattle industry and the broader U.S.-Canada livestock trade, which saw approximately 550,000 head of cattle cross the northern border in 2025 alone. If the parasite spreads beyond the initial control zone, it could disrupt a multi-directional trading relationship covering beef, dairy, breeding stock, and wool animals.
Texas Governor Greg Abbott declared a state of disaster on Friday, warning that the situation is likely to worsen. “This is likely to spread over the course of the summer,” Abbott said.
What Happened
The first confirmed case was detected Wednesday in a three-week-old calf in La Pryor, Texas — a town situated roughly 30 miles north of the Mexican border. Larvae were discovered in the calf’s umbilical area, a common entry point for the parasite.
A second infection was confirmed Friday in a one-month-old calf in neighboring Zavala County, approximately 5.6 miles from the original site. Critically, the second case fell inside the 20-kilometer control zone that federal authorities had established following the first discovery, suggesting the pest had already spread within that area before containment measures were fully in place.
In response, Canada’s food inspection agency announced a temporary ban barring cattle and horses that had been in Texas within the previous 21 days from entering the country. The U.S. Department of Agriculture confirmed both cases and has implemented quarantines, movement restrictions, and heightened surveillance across the affected region.
About the Parasite
The New World Screwworm is a parasitic fly that deposits its eggs in open wounds or mucous membranes of warm-blooded animals. Once hatched, the larvae burrow into living tissue and, if left untreated, can kill the host animal. The pest was considered eradicated in the United States in 1966 after an intensive sterile-fly release campaign. A subsequent flare-up occurred in the 1970s before the parasite was again suppressed.
The current outbreak did not originate domestically. The screwworm has been advancing northward through Central America and Mexico, and the discovery in South Texas represents its first confirmed re-entry into the United States in approximately 60 years.
Canadian officials noted that the parasite is unlikely to establish itself in Canada due to the country’s colder climate, but said the temporary import ban was a precautionary measure to prevent any possibility of introduction.
By the Numbers
- 2 confirmed screwworm cases in Texas as of Friday
- 60 years since the parasite last appeared in the United States
- 30 miles from the first detected case to the Mexican border
- 550,000 cattle imported from the U.S. to Canada in 2025
- 21-day lookback period under Canada’s temporary livestock ban
Zoom Out
The screwworm’s northward migration reflects a broader pattern of agricultural pests and livestock diseases expanding their range as trade corridors and climate conditions shift. The U.S. has faced similar cross-border biosecurity challenges in recent years, including outbreaks of foot-and-mouth disease and highly pathogenic avian influenza that prompted international trade restrictions. Texas, as the nation’s largest cattle-producing state, is particularly exposed to economic disruption when its livestock are subject to foreign import bans. The situation also underscores ongoing pressure on U.S.-Mexico border biosecurity infrastructure, which has been a recurring point of tension in Texas political debates.
What’s Next
Federal agriculture officials plan to deploy hundreds of millions of genetically altered sterile flies in the affected region — the same general method used to eradicate the pest in the 1960s. Authorities also intend to use trained sniffer dogs to detect the parasite in cattle before they move through the transportation system.
The scope of Canada’s ban and the duration of U.S. quarantine measures will depend on whether additional cases are identified outside the existing control zone. With Governor Abbott’s disaster declaration now in effect, state resources are expected to supplement the federal response as surveillance expands across South Texas.