Deaths from the outbreak of equine herpes virus rose to nine on Thursday, the latest in Oregon, that also reported four new cases while Idaho confirmed five new infections of horses to raise the total to 53 verified cases in the western United States.
The latest reports came as the United States headed into the Memorial Day holiday weekend attempting to contain an outbreak of a mutated neurological form of EHV-1 that was first detected at the National Cutting Horse Western Championships in Ogden, Utah the first week of May.
Throughout the vast area of western states–making up about one-third of continental United States, plus western Canada–affected by the spread of the disease, the latest tally compiled by dressage-news.com shows the death toll at:
Arizona (1), California (1), Colorado (2), Idaho (2), New Mexico (1), Oregon (1) and Utah (1).
California, which has been hardest hit by the disease with 18 confirmed cases–16 from the Ogden cutting horse event and two from a cutting horse show in Bakersfield, California–reported no new cases for the third straight day.
Like other states, California recommended that horses suspected of being infected should remain quarantined for 14 days after the last confirmation.
The U.S. Department of Agriculture said it would issue a report on the outbreak on Friday, an update on the single report it published a week ago.
EHV-1 and EHM are highly contagious among horses but do not affect humans
The outbreak of EHV-1 has affected only participants in the two cutting horse competitions. No horses in any other discipline or at any other competition venue have reported being infected.
Dozens of horse shows of various disciplines throughout the western states have been canceled, including several dressage competitions.
Some competitions that went ahead enforced biosecurity procedures that included backup quarantine stabling and round-the-clock veterinary care. However, widespread withdrawals were reported as competitors heeded recommendations to contain the outbreak and stayed home.
The spread of EHV-1 and its mutated EHM form in the western states surpassed one of the previous worst outbreaks among show horses, in South Florida in December, 2006, resulting in six deaths and threatening Florida’s winter circuit, the world’s largest horse show.
The number of confirmed cases of EHV-1 or EHM in the current outbreak, as compiled by dressage-news.com from official state reports, Thursday night were: California (18), Colorado (9); Idaho (5), Montana (1), Nevada (3), New Mexico (2), Oregon (4), Texas (1), Utah (7) and Washington (3).
Oregon reported that four horses tested positive for EHV-1, but not showing clinical signs of EHM, and all were in facilities that were under quarantine and directly connected to the Ogden cutting horse event.
“A fifth horse developed neurological signs and was euthanized.” the state reported. “It tested positive for EHM.”
Idaho reported Thursday that five horses at an EHV quarantined facility were confirmed positive for EHV-1. Two of the horses attended the cutting horse show in Ogden, and three were stablemates.
Among the competitions going ahead as scheduled over the Memorial Day weekend was Dressage at Flintridge in La Cañada-Flintridge in Los Angeles, that is the second of three qualifying shows across the country for young horses seeking to represent the U.S. at the world young dressage horse championships in Verden, Germany, in August.
Other U.S. Equestrian Federation-sanctioned competitions proceeding in the west include Dressage Derby I and II in Vacaville, California, Friday through Sunday and the 16th annual Spokane Sport Horse Spring Dressage in Washington.
In Colorado where two deaths and nine confirmed cases were reported earlier in the outbreak, Dressage in the Plains I and II in Peyton scheduled for Friday through Sunday and the Whispering Winds schooling show in Monument were canceled.
The Oregon Dressage Society advised that the Fort Vancouver Dressage Show and the Twin Rivers Summer Sizzler Practice Show scheduled for the Memorial Day weekend would not be held because of concerns over the EHV-1 outbreak and that many barns were voluntarily imposing a quarantine on their facilities.
Oregon, Colorado and Wyoming have imposed regulations on horses transported from other states.