Deadly Horse Virus Breaks Out Again

Nine months after a potentially fatal equine virus swept Western states, the disease is back.

Five new cases of equine herpes myoencephalitis (EHM), also referred to as neurological rhino, a mutated form of the equine herpes virus 1 (EHV-1), were reported at a facility in Orange County by the California Department of Food and Agriculture (CDFA).

Last May, equestrian events throughout the western United States were canceled due to an outbreak of the potentially lethal virus that began at an equestrian event at the Golden Spike Equestrian Center in Ogden, UT, and spread rapidly to horses in California, Washington, Nebraska, Colorado, Texas, Arizona, Nevada and Utah. 

EHM attacks the horse's neurological system and, in some cases, the horse must be euthanized. The virus is easily spread and has a high mortality rate. Signs of EHM in horses may include nasal discharge, lack of coordination, hindquarter weakness, recumbency, lethargy, urine dribbling and diminished tail tone. 

According to the CDFA, all of the cases have been confined to one unidentified facility in Orange County, where the horses are under quarantine. The CDFA described the property as a large multi-discipline facility, with no movement of any horses on or off the premises.

Last May, more than 400 horses were exposed to the virus in Utah; 54 of those horses returned to California after the event. Nearly half of the exposed horses contracted the virus. There were 22 confirmed cases in California by the CDFA and several of those horses had to be euthanized.

In response to the outbreak last year, which was first reported by Chatsworth Patch, throughout the months of May and June, many of Chatsworth's boarding stables and privately owned barns put themselves under voluntary quarantine. Local events were canceled, including Equestrian Trails Inc. Corral 54's Annual Trail Trials in Browns Canyon.  

"It was one of the few times we ever saw Chatsworth's trails empty of riders because people were so cautious of catching or spreading the virus," said ETI Corral 54 President Mary Kaufman.

Since the outbreak last May, 11 cases have been reported in California, but none were linked to the May 2011 incident.

Dr. Marta Granstedt, a large-animal veterinarian who practices in Chatsworth, advised last May, when the outbreak first hit, that horses should be kept current on their EHV-1 vaccinations, but to avoid vaccinating a horse if it shows signs of having the virus.  

Although there is no vaccination currently on the market that can make a "label claim" against EHM, vaccinating against EHV-1 is still advised to reduce a horse's chances of catching EHM.  

Charlotte Brodie of ETI Corral 54 told Chatsworth Patch, "Most horse owners know the importance of biannual shots to help keep their horses healthy. Each April and October, Corral 54 has a biannual vet clinic in Chatsworth at , with Dr. Marta Granstedt attending, to provide the community the opportunity to get their horses vaccinated without the extra cost of the 'call fee.' We are grateful to these folks for working with us to help promote a healthy living for our animals." 

If you think your horse has the virus or has been exposed to the virus, isolate it from other horses, practice good biosecurity measures, and call your vet immediately. 

The following advisory comes from the CDFA website:

CURRENT EHV-1 SITUATION:

ORANGE COUNTY:

January 11, 2012: A gelding displaying neurologic signs from an Orange County premises was confirmed positive for the neuropathogenic strain of Equine Herpes Virus-1. The gelding has been isolated, quarantined and is under veterinary care. The large multi-discipline facility has been quarantined with no movement of horses on or off the property. The potentially exposed horses on the premises are being monitored. A full epidemiologic investigation at the affected premises has been initiated by the CDFA Animal Health Branch.

January 12, 2012: Two additional horses displaying fever and respiratory signs have been confirmed positive for the neuropathogenic strain of Equine Herpes Virus- 1, on the Orange County premises. All horses on the premises remain under quarantine and being monitored for disease.

January 13, 2012: Two additional horses displaying a fever have been confirmed for the neuropathogenic strain of Equine Herpes Virus-1. There are a total of five confirmed positive cases on the Orange County premises. All horses on the property continue to be monitored.

January 14, 2012: There are no new cases. CDFA continues to monitor the situation.