Flesh-eating screwworm parasite spreads to a third US state as a dog is infested in an Arizona county bordering Mexico

Arizona has confirmed its first New World screwworm case after a local vet found a dog in Cochise County — which borders Mexico — with a heavily maggot-infested wound on its back on Monday evening. Lab results confirmed the infestation on Wednesday, making Arizona the third US state hit after Texas and New Mexico. State veterinarian Dr Ryan Wolker said officials had been preparing and were "acting swiftly" as federal authorities established a 20km restricted zone around the site.

Seventy-one screwworm cases have been detected across the US since June, with 18 currently active — up from just two last month.

The USDA is releasing sterile flies and increasing live animal surveillance around the Arizona site to combat the spread.

The outbreak, which began in Panama and Costa Rica in 2023, is complicating US efforts to reopen livestock imports from Mexico and ease record beef prices.