Parasitic screwworm detected in Texas calf decades after U.S. eradication

Federal officials discovered a New World screwworm on a cow in southern Texas, according to a Wednesday statement from Agriculture Secretary Brooke Rollins. Officials discovered larvae in the umbilical cord of a 3-week-old calf in Zavala County, Rollins reported. The U.S. Department of Agriculture immediately responded and has not detected any other larvae, according to a separate Wednesday statement from the agency.

How do they endanger livestock? Screwworms lay eggs in the wounds of warm-blooded animals, allowing the hatched larvae to feed on the animal. The maggot-like larvae use hook-like teeth to burrow into the animal and make the wound sites deeper. The flesh-eating parasites present a serious threat to livestock and wildlife, prompting the United States to officially eradicate the bugs in the late 1960s.

Officials took great efforts over the last year to protect American cattle from the latest screwworm outbreaks that slowly moved north from Central America to Mexico in recent years. The USDA is leading an aggressive response against this devastating pest, according to the federal agency.

Are humans at risk? Any warm-blooded animal may be infected, but human cases remain exceedingly rare. The Centers for Disease Control and Prevention reported the first documented U.S. case of a human contracting screwworm last August. A Maryland resident contracted the parasite after traveling to El Salvador, according to the CDC.

What kind of precautions are being taken to protect American cattle? Agriculture officials established a nearly 13-mile radius around where the larva was detected, and enacted quarantines, surveillance, and movement controls, according to the USDA. Officials planned to release sterile male screwworm flies to the area, which will mate with any females in the area, prompting the female to lay unfertilized eggs. Since female screwworm flies mate only once in their lifespan, the population in the area is expected to die out.

Dig deeper: Read my report in WORLD Magazine for more background on the screwworm.