New World Screwworm Found in Dog in Arizona

The discovery of a New World screwworm in a dog in Cochise County, Arizona, marks a significant development in the ongoing resurgence of this parasitic infestation in the United States. This case, confirmed by the Arizona Department of Agriculture, represents the first reported instance of the New World screwworm in the state and is part of a broader outbreak that has affected at least three states since June 2026.

The infected dog, currently receiving veterinary care, was found in Cochise County, which shares a border with Mexico—a region where the screwworm remains endemic. This geographic proximity raises concerns about the potential for further spread, particularly given that the New World screwworm (Cochliomyia hominivorax) is known to be highly invasive and capable of affecting a wide range of warm-blooded animals, including livestock, wildlife, and domestic pets.

Since June, there have been 71 confirmed animal cases across the region, with five of those involving dogs and one cat. Eighteen of these cases remain active, including an ongoing infestation in a wild elk in Pecos County, Texas, and a recent detection of a wild screwworm fly in a surveillance trap in Brewster County, Texas. These findings underscore the growing threat to both animal health and agricultural economies.

The New World screwworm is a flesh-eating fly whose larvae feed on living tissue, leading to severe wounds, bloody drainage, swelling, and behavioral changes in affected animals. While human infestations are rare, they can occur in areas where the fly is circulating. The U.S. Department of Agriculture has issued a press release to alert stakeholders, and the FDA has authorized Capstar (nitrenpyram) for both prevention and treatment in dogs and cats.

This outbreak is particularly concerning because the New World screwworm was previously eradicated in the U.S. through the sterile insect technique—a method that involved releasing sterilized male flies to reduce reproduction. However, the continued presence of the fly in Central and South America, combined with cross-border movement, poses a persistent risk of reintroduction.

Texas, with its large livestock industry and extensive ranchland, is especially vulnerable to a widespread outbreak, which could result in significant economic losses for ranchers and producers. The situation highlights the need for continued surveillance, rapid response protocols, and public awareness to prevent further spread.

What We Know

• A dog in Arizona was infected with New World screwworm. ¹²⁴⁵⁶
• The infected dog is receiving veterinary care. ¹²⁴⁵
• The state agriculture department reported the case. ¹²⁴⁵
• There have been 71 confirmed animal cases since June. ³
• Arizona has reported its first case of New World screwworm. ⁶
• The case involves a domestic dog located in Cochise County, Arizona. ⁶
• Five of the recent cases involve four dogs and one cat. ³
• Eighteen of the 71 cases are still active. ³
• An active case involves a wild elk in Pecos County, Texas. ³
• A wild screwworm fly was detected in a surveillance trap in Brewster County, Texas. ³
• New World screwworm flies lay eggs in open wounds, and their larvae feed on living flesh. ³
• Capstar and its generic equivalent, nitenpyram, were authorized by the FDA for both prevention and treatment of screwworm in dogs and cats. ³
• Animals at risk include cattle, horses, sheep, goats, pigs, deer, dogs, and occasionally cats. ³
• Human infestations are rare and mostly occur in areas where the fly is circulating. ³
• New World screwworm is not considered a food safety threat to beef and other meats. ³
• Symptoms of New World screwworm infestation include worsening wounds, bloody drainage, swelling, visible larvae, and behavioral changes. ³
• Texas has a large livestock industry and extensive ranchland, making it vulnerable to a widespread outbreak. ³
• Economic losses for ranchers and producers could result from a widespread outbreak. ³
• Screwworm was previously eradicated in the US using the sterile insect technique. ³
• The risk of New World screwworm reintroduction exists due to its presence in Central and South America. ³
• This is the third state to be affected by the New World screwworm. ⁶
• Cochise County borders Mexico. ⁶
• The U.S. Department of Agriculture issued a press release regarding this case. ⁶