The US Department of Agriculture (USDA) said on Friday that it has detected a second case of a dangerous livestock pest whose flesh-eating larvae can kill cattle.
“The new incidence of so-called New World screwworm (NWS) was detected in a calf in south Texas about 10 km from the first one, which was reported on Thursday,” the department said on X.
The outbreak has triggered a race to keep the pest from spreading.
The New World Screwworm fly was thought to be eradicated in the United States in 1966. But Florida experienced an outbreak in 2016 that primarily impacted deer and was eliminated the following year, according to the department.
The fly has remained present in South America and, in recent years has moved northward.
The first of these new cases, detected near the border with Mexico, has triggered alarm among ranchers, in particular those who raise cattle.
The flies lay their eggs in open wounds or mucous membranes of warm-blooded animals, where they hatch into larvae and feed on flesh. Left untreated, the infestation can be deadly, and the parasites can quickly spread.
The pest can also affect wild animals, pets and even people.
Texas has established a 20-kilometre quarantine zone, meaning all warm-blooded animals, including pets, must be inspected before leaving the zone.
The fly had been eradicated in the US in large part by dropping millions of sterile flies to mate with wild females.
US officials said, “some four million sterile flies are now being released weekly from the sky, and some four million more in the pupae stage are being deployed in ground release chambers.”
A USDA study in 2025 estimated a screwworm resurgence in Texas could cost the state’s economy $1.8 billion.
