Flesh-eating screwworms spread to third state and are attacking pets

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For a genuine fright this Halloween, you can turn your gaze to the southern border, where ravenous, flesh-eating maggots are festering and have taken to eating people’s pets.

This week, the country’s New World Screwworm (NWS) infestation spread to a third state, Arizona, which joins New Mexico and Texas in being plagued by the horrifying parasites. To date,74 animal caseshave been identified in the US since the flies re-invaded the country in June.

The flies lay hundreds of eggs in wounds and moist orifices of animals, and the resulting voracious maggots feast on their victims. The maggots resemble screws and tortuously bore and twist into living flesh, causing severe, sometimes fatal wounds, before dropping to the ground to develop into adults.

Because of their ability to ravage livestock, the flies were eliminated from the country in the 1960s through aerial releases of sterile male flies, which thwart successful breeding. For years, they were held at bay using a biological barrier along the Darién Gap at the border of Panama and Colombia. But the barrier was breached in 2022, and the flies have made their way back to the US through Central America.

No one is safe

While they are largely seen as a threat to the livestock industry, they can also devastate wildlife, domestic pets, and in rarer cases,humans. According tothe latest datafromMexico’s Ministry of Health, the country has confirmed 806 cases of human screwworm infestations since the flies reemerged. Nine people died from the savage maggots.

In the US, most of the 74 confirmed cases have been in livestock. But some of the cases have been in domestic pets, mainly dogs. Just this week, the US Department of Agriculture recorded four new cases in domestic dogs—which includes the new detection in Arizona—as well as a domestic cat in New Mexico. That brings the pet total to 10 cases since the flies reemerged. The US has also detected one case in a wild elk, which was reported last week.

Arizona’s agriculture department said this week that the state’s index case was identified in a dog in Cochise County, which borders both New Mexico and Mexico. A local veterinarian examined the poor pup on October 26 and found a wound on the canine’s back that was “heavily infested with maggots consistent with NWS characteristics.”

“We remain prepared and vigilant, and we urge all livestock owners, pet owners, and other animal industry partners to continue to monitor animals closely and report any unusual wounds consistent with NWS immediately,” thestate said in an announcement.

The USDAconfirmed the infectionand said it was working closely with Arizona on a joint response to the expanded infestation.

Senior Health Reporter

Senior Health Reporter

Beth is Ars Technica’s Senior Health Reporter. Beth has a Ph.D. in microbiology from the University of North Carolina at Chapel Hill and attended the Science Communication program at the University of California, Santa Cruz. She specializes in covering infectious diseases, public health, and microbes.

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