The USDA confirmed on Wednesday the first detection of the New World screwworm, a flesh-eating parasite, in US wildlife: an elk in Pecos county, Texas.

How the case was found

According to the USDA statement, the infected elk was located on a game ranch and was reported after being harvested by a hunter.

Surveillance and zone changes

State and federal agencies are responding on two fronts:

• •The Texas animal health commission will modify a previously established infested zone.
• •The USDA and the Texas parks and wildlife department are conducting additional wildlife surveillance in the area.

Hunters urged to stay alert

Alan Cain, the Texas wildlife division director, urged hunters and landowners to stay vigilant for signs of the parasite while out in the field this season.

Background: the parasite's return north

Eradicated from the US decades ago, the pest has surged north from Central America through Mexico. That spread prompted Washington to impose a more than year-long ban on Mexican cattle imports. The US halted livestock imports from Mexico last year, then resumed trade in August at an Arizona port as part of a phased reopening plan. The halt tightened US cattle supplies and pushed beef prices to record highs.

This year's screwworm cases in the US number in the dozens, including on a horse and on a dog. In June, the parasite was detected on a calf in Texas's Zavala county.