Warming climate is helping the screwworm spread

The USDA has now confirmed five cases of the New World screwworm, and for the first time, the flesh-eating parasite was found outside of Texas, and in a pet.

The fifth case was found in a small dog in New Mexico in Lea County, which borders Texas.

The pest, once eradicated in the 1960s is back, this time on a warmer playing field, thanks to climate change.

The weather connection

Lee Haines, an associate research professor of biological sciences at the University of Notre Dame told the Associated Press that climate change is a key element in the spread of a tropical species that thrives in warm weather. 

Warmer temperatures are expanding the fly's habitat and cold snaps that killed them off each year in marginal habitats are becoming less frequent and less severe, she said.

Canada temporarily stopped importing cattle, horses or other livestock from Texas on Friday. The parasites prefer humid areas where temperatures are at least 77 F (25 C), making them more of a summer problem up north.

Will screwworm raise beef prices?

The fly does not infest meat, fruit or food, so Agriculture Secretary Brooke Rollins said it’s unlikely to damage beef production or the prices you’ll see at the register tomorrow.

But with U.S. cattle herds at their lowest in 75 years, a wider outbreak could put pressure on an already tight supply.

Scientists expect new cases could pop up in the coming days and weeks, but it doesn't mean screwworm is spreading rapidly, said Edward Burgess, a University of Florida entomologist who studies the fly.

“When that first case is seen, everyone is being vigilant and their eyes are on it more intensely,” Burgess said. “And when you are looking for something, you are more likely to see it.”'

Why livestock are vulnerable

The larvae of the screwworm burrow or screw into the flesh of warm-blooded animals through wounds or openings. Occasionally, even people can be infested.

Livestock are particularly vulnerable because of how they're handled, Lee Haines explained, saying standard practices with cattle can break the skin, including shearing and dehorning, or even moving them in and out of corrals can cause scrapes and cuts.

Stephen Diebel, a Texas rancher and president of the Texas & Southwestern Cattle Raisers Association, added that even wounds “as small as a tick bite,” can put cattle at risk.

Death can result if an infestation is not treated, though a dozen treatments have been approved for use in a variety of species.

What’s being done

Texas State Veterinarian Bud Dinges imposed a 12-mile quarantine zone covering much of Zavala County, and a small part of neighboring Uvalde County. Animals cannot leave that zone without being inspected.

Diebel, whose family ranch is about 200 miles east of the quarantine zone, said ranchers are proactively giving injections that prevent screwworm infestation. They’re also taking extra care to treat wounds from ear tagging and other practices and keeping a close eye for signs of illness.

The USDA is ramping its program of dropping millions of sterile male flies to eventually eradicate the parasites.

The goal is to have enough sterile flies to stop the pests from returning in 2027 after the winter kills off most of them, USDA Secretary Brooke Rollins said at a news conference this week.

Texas officials encouraged ranchers to keep a close eye on their herds and local wildlife. There's now a 24-hour screwworm hotline and a website and map for reported cases.

The Associated Press contributed to this report.