Agricultural authorities on both sides of the US–Mexico border are intensifying efforts to contain the resurgence of the New World screwworm, a flesh-eating maggot that burrows into livestock and occasionally humans. The parasite has spread north through Central America and southern Mexico, triggering the first detections in central Mexican herds in decades and a fourth confirmed human infection in El Salvador. Experts warn the pest is now within about 370 miles of the Texas border and is more likely than not to reach US herds. The economic fallout is already severe. Mexico’s Council for Agricultural Development estimates producers have lost about $1.3 billion after US authorities repeatedly suspended live-cattle imports, blocking 650,000 head from crossing the border since late May. Mexico’s National Union of Agricultural Workers is urging the government to halt bovine imports from Nicaragua, Honduras and Guatemala, citing active outbreaks and the illicit movement of an estimated 800,000 animals that it says has depressed domestic prices by up to 40 percent. Mexican officials have rolled out emergency veterinary measures. In Chiapas, the state most affected, authorities are in a second phase of distributing the antiparasitic drug ivermectin, aiming to treat more than 30,000 cattle this month as part of a broader plan covering nearly one million head statewide. Producers in Jalisco, the country’s top beef-exporting state, have drafted a prevention strategy even though no cases have been confirmed there. Mexico and the United States have also signed a joint action plan that includes building a sterile-fly plant in Chiapas capable of producing 100 million insects a week. Washington is expanding its own biosecurity lines. Agriculture Secretary Brooke Rollins last week announced a $750 million factory in Edinburg, Texas, that will triple US capacity by breeding 300 million sterile flies weekly, complementing an $8.5 million dispersal facility nearby. The USDA will invest an additional $100 million in traps, lures and other technologies to slow the pest’s advance, while Texas has activated a New World Screwworm Response Team. Officials say aggressive intervention is needed to shield a US cattle industry worth roughly $15 billion from a parasite that was declared eradicated domestically in 1966 but caused severe losses during a 1972-76 flare-up.