| What is old can always be made new again. The New World Screwworm, a fly whose larvae feed on living tissue, was one of the deadliest and most persistent blights on America’s livestock from the 1930s to the 1980s. Capable of eating a full-grown steer alive in about a week, it decimated wildlife and caused hundreds of millions of dollars in damages to ranchers each year. Now, after being largely eliminated from North America using a novel scientific breakthrough, the screwworm is poised to return to the southern US. In the late 1930s, scientists realized that if they sterilized enough male screwworms, they could ensure new larvae were non-viable, interrupting a screwworm population’s ability to reproduce. It would take another 60 years, but the US established an actively maintained “wall” of sterilized flies to contain the worms south of Panama, with a plant that today still produces 100 million sterile screwworms each week. The effort was so successful that in the intervening years a generation of people in Central and North America simply forgot to worry about the screwworm. That includes veterinarians. “It’s extremely likely that patient zero in the US will be a dog or a cat in a small animal clinic that hasn’t been trained to spot the screwworm,” said Dr. Christopher Womack, a livestock veterinarian. “They’ll just treat it like a regular wound.” This past week the US Department of Agriculture raised the stakes on the cross-border fight to prevent the screwworm’s return, with Secretary Brooke Rollins threatening to close the US border to Mexican livestock if Mexico did not allow the US to fly planes full of sterile flies over its most infested regions. Mexico has agreed to a deal, and the US committed to looking at building domestic means of defending itself: At the moment, all sterilized flies are produced in Panama, and “all” amounts to a fraction of what experts estimate will be needed. The parasite, which thrives in warm weather, has a long summer ahead of it. If a major infestation runs unchecked, it could have a significant impact on American consumers. Cattle supplies are already tight, and the damages would likely drive up the cost of beef — just as avian flu led to record egg prices and caused billions in damages. It seems increasingly likely that the screwworm can be slowed, but not stopped, in its march northward. And there is fear that it may already be too late. Dr. Grace VanHoy, a veterinarian and assistant professor of clinical livestock medicine and surgery at UC Davis, said, “There is a very real chance that [the screwworm] may already be here on wildlife, and it just hasn’t been detected yet.” — Madison Darbyshire, Bloomberg Weekend Read more: A Deadly Parasite’s Return Threatens US Ranchers Too Young to Remember It | 
