Texas confirms more New World screwworm cases

Texas confirms new screwworm infections, USDA adds cases in a calf and a dog as Canada tightens livestock imports, a parasite last beaten by mass sterile-fly drops returns to test border controls

Texas has recorded additional confirmed cases of New World screwworm, a flesh-eating parasite that threatens livestock and can infest any warm-blooded animal. Global News reports the U.S. Department of Agriculture announced two new infections on a Monday — in a calf and a dog located hundreds of miles apart — bringing the state’s total to four confirmed cases.

The immediate risk is not only animal health but the knock-on effects of trade and movement controls once buyers assume the problem will spread faster than officials can map it. Canada has already imposed temporary restrictions on livestock imports from Texas, according to Global News, a step that can ripple through pricing and logistics even before large production losses show up. Texas is the largest cattle state in the U.S., with a cattle industry valued at $17 billion in the source material, which makes the state a natural transmission corridor as well as a political pressure point.

Screwworm’s biology makes it an awkward fit for policies designed around paperwork and checkpoints. The larvae feed on living tissue and fluids, and females lay eggs in open wounds or mucous membranes; routine handling practices such as dehorning, shearing, corralling, and even small injuries like tick bites can create entry points. Birth is another high-risk moment for cows and calves. Global News notes that untreated infestations can be fatal, and that approved treatments exist across species, but the larger challenge is detection and response speed across wide areas.

The U.S. has dealt with this before. Screwworm was a major problem for ranchers from the 1930s through the 1960s, and eradication was achieved by breeding sterile male flies and releasing them from planes — a program that worked because it was scaled industrially and sustained over time. The parasite was later contained for years near the southern end of Panama, but it reappeared with an outbreak in Panama in early 2023, followed by rising cases in parts of Central America; it was detected in Mexico in late 2024, Global News reports.

USDA Secretary Brooke Rollins has said the fly is unlikely to damage beef production. Markets and trading partners, however, react to uncertainty, not reassurance: a handful of confirmed cases can be enough to trigger restrictions, reroute shipments, and raise the value of “clean” origin claims.

The latest confirmed infections include animals found far apart inside Texas. That distance is now part of the case file, alongside a parasite that does not recognise borders.