American tests have found that the lethal screw-fly parasite poses a threat to cow herds.

A deadly parasitic disease in cattle has been detected in the United States for the first time in nearly a decade, posing a new risk to the already dwindling American cattle population, which is at its lowest levels in 75 years. The U.S. Department of Agriculture reported that samples from southern Texas confirmed the presence of New World screw-worm in a three-week-old calf in Zavala County. This detection of the deadly parasite comes at a critical time for the U.S. beef industry: a reduction in cattle stocks has led to record high prices for beef, and measures may be implemented to control the transport of livestock across regions. The market reacted in anticipation on Wednesday even before the official announcement of the case: Tyson Foods fell by 4.2%, closing at a five-month low, while JBS's U.S. stock price hit a new low for the company's nearly one-year listing in the American market.