The New World screwworm (NWS) has been found in a Texas calf, marking the first US detection of the pest that damages livestock herds in decades, the US Department of Agriculture (USDA) said.
The pest was detected in a three-week old calf in La Pryor, Texas, around 100 miles from the Mexican border. NWS larvae burrow into the flesh of living animals, causing "serious damage to livestock and economic losses", the USDA said.
NWS-infected animals can be returned to the herd after treatment, but some may be euthanized if treatment is not possible. NWS infections do not lead to culling like bird flu cases. NWS can reduce calf births and cut milk output, which affects both beef and dairy production. The US cattle herd totaled 86.2mn head as of the start of 2026, the lowest level since 1951, USDA data said.
Ranchers will need to monitor herds closely for open wounds, where the parasite often enters, adding to the time and labor costs of raising cattle.
"USDA invested heavily in the tools needed to eliminate NWS ever since cases started increasing in Central America and Mexico," USDA undersecretary for marketing and regulatory programs Dudley Hoskins said. "The United States has defeated this pest before, and we will do it again."
The USDA will implement its NWS response plan, which includes a20km (12.4 mile) radiusquarantine zone around the detection, increased releases of sterile NWS flies, trapping of NWS flies at the Mexican border, and wildlife surveillance.
Texas agriculture commissioner Sid Miller asked President Donald Trump to "declare New World screwworm a national agricultural emergency and marshal every available federal resource toward eradication".
NWS was last detected in US livestock in 1976, also in Texas, USDA said. It was also found in wildlife and domestic animals in the Florida Keys in 2016 but was eradicated before infecting livestock.
Fatality rates for untreated livestock are close to 100pc, but they fall dramatically with early detection and treatment, USDA said.
