US Says Screwworm Spreads to Wildlife for First Time

New World screwworm has been found in an elk in Texas, marking the first confirmed case of the potentially deadly animal parasite in US wildlife.

The pest, which infests livestock wounds, was detected in an elk on a game ranch in Pecos County, the US Department of Agriculture said late Wednesday. Spread among wildlife has been a key concern for cattle ranchers since the animals travel through the same terrain that their herds graze on.

Screwworm was first detected in Texas livestock in early June. The spread of the parasitic fly, whose larvae burrow into animal wounds, has since caused 59 cases in the country, according to the USDA. Seven remain active in Texas and New Mexico, affecting cattle, horses and a dog, the agency said.

New World screwworm (NWS) flies at a sterile screwworm fly production facility in Metapa, Chiapas state, Mexico.

The latest case was reported after an elk was collected by a hunter, “underscoring how vital hunters, landowners, and outdoor enthusiasts are in spotting and reporting NWS early,” the USDA said in a post on X, while asking for vigilance as the hunting season continues in Texas.

“Hunters and others who spend time outdoors near infested areas are often among the first people to encounter affected wildlife, making their observations especially valuable to surveillance and response efforts,” the USDA said in Wednesday’s statement.

Screwworm, which can be deadly to livestock if left untreated, was also found in one wild fly in Brewster County, Texas in late September. It was caught in one of the USDA’s more than 100 screwworm-specific fly traps along the US border.