It is not surprising that equine herpesvirus 1 (EHV-1) is so well adapted to infect horses. Professor Peter Timoney, with the Maxwell H. Gluck Equine Research Center at the University of Kentucky, says EHV-1 is believed to have co-evolved with horses over millions of years. This co-evolutionary relationship resulted in the development of a life-long carrier state in a high percentage of infected horses. This involves viral latency (silent infection) of various sites (the trigeminal ganglia in the central nervous system, respiratory lymphoid tissues, and CD3+ T lymphocytes in the blood). Latency ensures the perpetuation of EHV-1 by serving as a virus reservoir for infection and dissemination in susceptible populations.