# New World Screwworm Infestation Expands to Arizona Parasitic screwworm outbreak reaches third US state, impacting livestock and domestic pets. - **Source:** [Ars Technica - All content](https://brifing.si/source/b728770c-8dda-457a-8986-84879c9fc42c) - **Published:** 2026-10-30 - **Topic:** [Business](https://brifing.si/c/business) - **Original article:** - **On Brifing:** https://brifing.si/s/89046073-723c-45b2-8678-a4da3de66dae ## Outbreak Reaches Arizona Borders The New World Screwworm infestation has officially expanded into Arizona, marking the third US state affected since the parasites re-emerged in June. This development follows confirmed cases in Texas and New Mexico. Authorities are currently managing a total of 74 identified animal cases across the country, signaling a concerning geographic spread of the infestation. ## Biological Mechanism of Infestation These flies deposit hundreds of eggs into open wounds or moist orifices of living hosts. The resulting maggots, which resemble screws, bore into flesh to feed, causing severe and potentially fatal injuries. Once mature, the larvae drop to the ground to complete their development into adult flies, perpetuating the cycle of infestation. ## Historical Context and Barrier Breach The United States successfully eliminated these flies in the 1960s using sterile male fly releases. For decades, a biological barrier at the Darién Gap between Panama and Colombia prevented re-entry. However, this critical barrier was breached in 2022, allowing the flies to migrate northward through Central America and eventually re-enter the United States. ## Impact on Domestic Pets While primarily a threat to the livestock industry, the parasites are increasingly affecting domestic animals. Recent data confirms 10 total cases in pets, including dogs and cats. The US Department of Agriculture reported four new cases in dogs and one in a cat this week, highlighting the growing risk to household animals. ## Arizona Index Case Details Arizona’s first confirmed case was identified in a dog located in Cochise County, a region bordering both New Mexico and Mexico. A local veterinarian discovered the infestation on October 26, noting a back wound heavily populated with maggots. The USDA has since confirmed the diagnosis and is coordinating a joint response with state officials. ## Broader Regional Health Implications The threat extends beyond US borders, with Mexico reporting 806 human screwworm infestations since the flies re-emerged. Tragically, these cases resulted in nine human deaths. While US cases remain concentrated in livestock and pets, the regional data underscores the potential for severe health consequences if the infestation is not effectively contained and managed. ## Surveillance and Reporting Protocols State agriculture departments are urging livestock and pet owners to maintain high levels of vigilance. Owners are instructed to monitor animals closely for any unusual wounds that appear consistent with screwworm characteristics. Immediate reporting of such findings is essential for the USDA and state partners to track the spread and implement necessary control measures. ## Future Containment Strategy The USDA continues to work closely with affected states to manage the expanded infestation. Given the history of successful eradication through sterile male fly releases, authorities are likely to prioritize similar biological control strategies. Continued monitoring of wildlife, such as the recent elk case, remains a critical component of the ongoing containment efforts. ## Sources covering this story - https://arstechnica.com/health/2026/10/flesh-eating-screwworms-are-feasting-on-pets-4-dogs-and-cat-attacked-this-week/ — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._