In the spring of 2021, Cynthia and John Grano, who own a cattle operation and sell performance horses in Culpeper County, Virginia, started noticing some of their cows slowing down and acting "spacey." They figured the animals were suffering from anaplasmosis, a common infectious disease that causes anemia in cattle. But Melinda McCall, their veterinarian, had warned them that another disease carried by a parasite was spreading rapidly in the area.
After a third cow died, the Granos decided to test its blood. Sure enough, the test came back positive for the disease: theileria. And with no treatment available, the cows kept dying. In September, by which time the couple had already lost six cows and seven calves, Cynthia noticed a cow separated from the herd. She was walking up to it when it suddenly charged at her and knocked her over, breaking her shoulder blade. By that afternoon, the cow was dead.
[...] Theileria, which is in the same family as malaria, is being transmitted largely through the Asian longhorned tick, an invasive species first discovered in the US in 2017. The tick is native to Korea, China, Russia, and Japan. As it has spread in the US, so has theileria; the disease has been found in cattle in West Virginia, North Carolina, Tennessee, Kentucky, Pennsylvania, and Kansas. Some sale barns in Virginia saw the prevalence of theileria increase from two to 20 percent in just two years.
Theileria can cause cows to abort their fetuses. It can also cause anemia so severe that a cow will die. In Australia, where the disease has been spreading since 2012 and now affects a quarter of the cattle, theileria costs the beef industry an estimated $19.6 million a year in reduced milk and meat yields, according to a 2021 paper. In Japan and Korea, the combined loss is an estimated $100 million annually. Kevin Lawrence, an associate professor at Massey University who studies theileria in New Zealand, says that country has managed to avoid abortions because 95 percent of cows calve in the spring there, the same season he's seen theileria infecting cows. In the US, however, calving season can be year-round. "I think in America, you're going to see abortions," he says. "You're going to see deaths."