Neurologic Equine Herpesvirus at California Showgrounds

One horse has been euthanized due to neurologic equine herpesvirus with others in quarantine after being exposed at a Sonomoa County showgrounds.
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One horse has been euthanized due to neurologic equine herpesvirus with others in quarantine after being exposed at a Sonomoa County showgrounds.

The California Department of Food and Agriculture (CDFA) confirmed one case of neurologic equine herpesvirus—with one non-neurologic EHV-1 horse—at a showgrounds in Sonoma County last week. Other horses have been quarantined and tested.

The report from the Equine Disease Communication Center noted:

"A 6-year-old Warmblood mare displaying neurological signs has been confirmed positive for equine herpesvirus myeloencephalopathy (EHM, or neurologic equine herpesvirus) secondary to EHV-1. She attended a show in Sonoma County from July 19 to July 24 but did not compete, and event management has notified all participants to monitor temperatures twice daily and report any fevers or neurologic signs to their veterinarians and CDFA, as well as isolate all horses returning from shows at their home premises for at least 7 days. 

"CDFA was onsite, and 19 exposed horses from the index mare’s barn were removed from the show facility and have been isolated and quarantined at the home premises in Sacramento County with the remaining 18 horses at the home premises with twice daily temperature monitoring and enhanced biosecurity measures. 

"Six horses from the home premises displaying fever and/or limb edema have also tested positive for EHV-1. A 15-year-old Warmblood gelding at the home premises that was febrile and tested positive for EHV-1 began displaying neurological signs, ataxia, urine dribbling and cranial nerve deficits and was moved to isolation under quarantine at a veterinary hospital for care. CDFA continues to actively monitor the situation.

In an update, the California Department of Food and Agriculture reported:

"The 18 horses from the index case’s origin premises that attended the Sonoma County event returned to their home premises in Sacramento County on Sunday, July 25, and are quarantined. The horse in this cohort with a fever on July 24 with tests pending was confirmed positive for EHV-1, remains isolated at the home premises, and has been afebrile since Saturday July 24. 

"On Monday July 26, CDFA staff performed a site visit at the home premises in Sacramento County. One horse on the Sacramento home premises that did not attend the Sonoma County event and had previously tested positive for EHV-1 (fever only) became neurologic on Monday July 26 and has been sent to an offsite veterinary hospital for treatment. He is in stable condition and was confirmed negative for EHV-1 on Monday, July 26. 

"One additional horse at the home premises that did attend the Sonoma County event and has remained afebrile also became neurologic on Monday July 26, has been sent to an offsite veterinary hospital for treatment, and was confirmed negative for EHV-1 on Monday July 26. She is currently alive and in stable condition. 

"One additional horse that was housed in the same barn at the Sonoma County event presented with fever and mild neurologic signs on Saturday July 24, was sent to an offsite veterinary hospital for treatment and was confirmed negative for EHV-1 on Monday July 26. He is currently alive and in stable condition. 

"The three remaining horses in this same barn returned to their home premises on Saturday July 25 and are isolated with temperature monitoring and no fevers or clinical signs have been detected. 

"The total number of confirmed cases in this incident are: 1 confirmed EHM case (EHV-1 positive with neurologic signs), 1 new confirmed EHV-1 case (fever and/or edema) only, with 4 previously presumptive positive EHV-1 cases (fever and/or edema only) that have subsequently retested and confirmed negative. 

"In total, 1 horse in this incident has been euthanized and the other affected horses are alive and under veterinary care. 

"As of Monday July 26, there is no evidence of ongoing EHV-1 spread at the Sonoma County facility following removal of all known affected and immediately exposed horses. A complete facility quarantine will not be implemented there unless ongoing disease spread is confirmed. 

"The decision for individuals to attend an event at this premises within this timeframe should be discussed with their veterinarians and will be at the owner’s and/or trainer’s own discretion and risk. CDFA recommends that any horses that attended or are currently attending the Sonoma County event be temperature monitored for at least seven days and isolated at least 30 feet from other horses when they return to their home properties. 

"CDFA was onsite at the Sonoma County event premises on July 27 and continues to actively monitor the situation."

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