First New World Screwworm Case in US Wildlife Confirmed in a West Texas Elk

The United States has recorded its first known case of New World screwworm in wildlife. The U.S. Department of Agriculture and the Texas Parks and Wildlife Department announced on Oct. 21 that laboratory testing confirmed screwworm larvae in a female elk harvested by a hunter in Pecos County, West Texas.

The animal was taken on a game ranch and reported by the hunter, officials said. The confirmation is the first known detection of the flesh-eating parasite in U.S. wildlife, according to the USDA’s Animal and Plant Health Inspection Service.

“Early reporting is one of the most important tools we have to protect wildlife, livestock, and pets in the United States,” the USDA said in a news release.

Tracking the spread

The Texas Animal Health Commission said it will adjust a previously established infested zone in response to the discovery. Federal and state agencies are also conducting additional wildlife surveillance in the surrounding area to determine whether other animals have been affected.

The detection comes as authorities track the northward spread of the parasite, which was eradicated from the United States decades ago. In recent years it has surged north from Central America through Mexico.

Separately, the New Mexico Department of Agriculture confirmed on Oct. 21 that it identified a screwworm case in a beef cow in the state’s Otero County, where surveillance and trapping efforts have been expanded around the affected area. As of Oct. 22, the USDA reported 61 screwworm cases in animals across Texas and New Mexico.

The elk is the second milestone case this year. In June, the agency confirmed screwworm in a 3-week-old Texas calf, the first known U.S. case in decades and the closest the parasite had come to reestablishing itself north of the Mexican border since its eradication in the 1960s.

Hunters urged to watch for signs

Texas wildlife officials are urging hunters to inspect harvested animals carefully during the fall hunting season and report anything suspicious. Hunters are often among the first people to encounter infested wildlife, the USDA said, and their reports play a large part in surveillance efforts.

“We encourage all hunters and landowners to be vigilant for signs of New World screwworm while they are out in the field this season,” Texas Wildlife Division director Alan Cain said in a statement.

Warning signs, according to the Texas Parks and Wildlife Department, include animals that appear irritated or depressed, lose their appetite, shake their heads, isolate themselves from other animals, or give off a foul odor from wounds, as well as visible maggots in injuries. After a harvest, hunters are encouraged to inspect the eyes, ears, nose, mouth, genital areas and any wounds on the animal for signs of infestation.

The New World screwworm is a parasitic fly whose larvae feed on the living tissue of warm-blooded animals, according to the USDA. It can affect livestock, wildlife and pets, and in rare cases people and birds. Infestations begin when an adult female fly lays eggs in an open wound or body opening; after hatching, the larvae burrow into the wound and feed on living tissue for about a week before dropping to the ground to pupate and emerge as adult flies. Adult screwworm flies have metallic blue-green bodies, orange eyes and three dark stripes across their backs.

The pest was eliminated in the United States through a long-running sterile fly program, but outbreaks in Central America and Mexico have raised fears that it could regain a foothold in North America. To slow its spread, the United States suspended livestock imports from Mexico for more than a year before resuming shipments through a phased reopening that began in August. The restrictions tightened cattle supplies in the United States and contributed to record-high beef prices.

Reporting based on coverage by USA Today.