The New World screwworm infestation in the United States has spread to Arizona, adding a third state to the list of areas affected by the parasitic fly. New Mexico and Texas had previously reported cases, and the USDA has identified 74 animal infections nationwide since the flies re-entered the country in June.
Screwworm flies lay hundreds of eggs in wounds and other moist openings on animals. After hatching, the larvae feed on living tissue, creating severe wounds that can sometimes be fatal. The larvae are named for their screw-like appearance as they burrow into flesh.
Although the infestation is primarily considered a threat to livestock, screwworms can also affect wildlife and domestic animals. The available report specifically notes that pets have been attacked, widening concern beyond the agricultural sector. Humans can also be affected in rarer cases.
The United States eradicated the flies in the 1960s by releasing sterile males from the air, preventing successful reproduction. A biological barrier maintained along the Darién Gap between Panama and Colombia later helped keep them away from the country. That barrier was breached in 2022, allowing the flies to move north through Central America.
Mexico’s latest health ministry data records 806 confirmed human screwworm infestations since the species re-emerged there, including nine deaths.
Sources: Ars Technica.