Four horses have died and a dozen more have turned up sick at a North Carolina stable, and officials are searching for a source of the illness. New Hope Stables in Hertford in Perquimans County reports no one knows what made the horses sick. A Facebook post by the stable says almost all infectious diseases have been ruled out, and that the focus is shifting to poisoning. The horses were all tested for coronavirus and other diseases, and all the tests came back negative. The post also said the stable is working with the N.C. Department of Agriculture to determine the cause.