New World Screwworm Found in Arizona Dog

Arizona has become the third U.S. state to confirm a case of New World screwworm after a dog in Cochise County was found to be infested. The New World screwworm is a parasitic fly, meaning it lives off other animals and can cause serious harm. The case was reported on Wednesday, and officials say the county where it was found shares a border with Mexico. Scientists ran tests on the dog and confirmed the screwworm was present.

The U.S. Department of Agriculture, known as the USDA, said screwworm is a "devastating pest." The fly's larvae — which are also called maggots — burrow into the flesh of living, warm-blooded animals. This causes painful and dangerous wounds that can become life-threatening if not treated. The dog that was found infested had a wound full of maggots that matched what screwworm infestations look like.

Arizona's State Veterinarian, Dr. Ryan Wolker, said officials were ready for this moment. "We have been preparing for this possibility for a long while and are acting swiftly," he said. State agriculture workers had been watching for screwworm cases and moved quickly once the dog's case was confirmed. Their fast response is meant to stop the pest from spreading further.

The USDA has now confirmed 71 animal cases of screwworm since June, including cases in Texas and New Mexico. Last week, the first wildlife case was also reported. For many decades, screwworm flies had been mostly wiped out in U.S. livestock, so this recent return has alarmed farmers and animal health experts. Officials have been working hard to contain the pest before it spreads more widely.

Health officials say the risk to people is very low right now. The Centers for Disease Control and Prevention, or CDC, reports that there have been no confirmed human cases of screwworm caught inside the United States. People who work closely with animals should still be careful and watch for any unusual wounds on their animals. The best way to protect animals is to check them regularly and contact a vet right away if something seems wrong.

The United States had stopped most cattle imports from Mexico back in November 2024 after screwworm was found there. Some of those cattle imports have since been allowed to resume. Officials continue to monitor animals crossing the border closely. Keeping a tight watch on animals entering the country is one of the most important steps in preventing screwworm from spreading further into U.S. states.