The disease is called Equine Infectious Anemia (EIA) and it is tested for with a coggins test. EIA is a viral disease which is spread by insects which bite an infected horse and then spread the virus to an uninfected horse. The symptoms of EIA are anemia, high fevers (>104 F), weakness, lethargy, irregular heart rate and rhythm, and sudden death. Hope this answers your question. Best of luck.