The Animal and Plant Health Inspection Service (APHIS) of the US Department of Agriculture issued its final report on an outbreak of the potentially deadly disease that was linked back to the National Cutting Horse Association Western National Championships in Ogden, Utah, from April 29 to May 8.
APHIS said the report would be its last, saying there had been no new cases and no new premises affected since its report the previous week.
"Disease spread in connection with this incident has been contained and no further situation reports will be generated," it said.
The outbreak left 13 horses dead, after the animals developed serious symptoms relating to the neurological form of EHV-1. Ten of the horses that succumbed to the disease has attended the Ogden. The other three caught the disease from horses returning home.
EHV-1 infection in horses can cause respiratory disease, abortion in mares, neonatal foal death, and/or neurologic disease.
The neurologic form of EHV-1 is called Equine Herpesvirus Myeloencephalopathy (EHM).
While EHV-1 and EHM are officially listed as reportable diseases in only some states, private veterinary practitioners are encouraged to notify their State Animal Health Officials of any suspected or confirmed cases, regardless of current official state reporting requirements.
In all, there were 90 confirmed cases of EHV-1 or EHM, 54 of which were in horses that attended the Ogden event.
Ten states reported cases - Arizona, California, Colorado, Idaho, New Mexico, Nevada, Oklahoma, Oregon, Utah and Washington.
APHIS figures show a total of 421 horses were potentially exposed at the Ogden event. In all, 1685 other horses were considered subsequently exposed as the competing horses return to their home states.
Across western states, 242 premises were listed as exposed and placed under restrictions, with 62 of these premises having suspected or confirmed cases.