The neurologic form of equine herpesvirus type 1 (EHV-1) was confirmed as affecting horses at Churchill Downs in mid-May. Three barns remained under quarantine until horses in those barns met requirements by May 24 to begin training on the track during separate hours from the general horse population. Triple Crown horses that ran in the Preakness were in unaffected barns at Churchill, so they were not impaired by the quarantines and were able to travel to Maryland for the May 21 race.

Five animals showed evidence of the neurologic form of EHV-1, with the first horse showing signs beginning around May 10. One horse in each of two barns was euthanatized after the animal’s condition progressed to a recumbent state. EHV-1 was confirmed in each of these animals. The third barn had three animals showing a milder neurologic disorder. Horses in these three barns were quarantined and segregated from the general equine population beginning May 17.

Prior to horses in a quarantined barn being permitted access to the track, no horse in that barn was to have shown a fever or displayed clinical signs of an equine herpesvirus infection during the past seven days.

Blood samples were collected from each barn’s entire population and submitted to the University of Kentucky’s Livestock Disease Diagnostic Center, where they were screened for EHV-1 by a polymerase chain reaction (PCR) assay. When all of the horses in the barn were found to be negative, the animals were allowed restricted access to the track for exercise. However, those horses were to remain under quarantine and not be allowed to mix with the general horse population at Churchill Downs