Veterinarians are still working to determine the extent of a multi-state outbreak of neurologic equine herpesvirus (EHV-1). The number of horses confirmed or suspected to have EHV-1 remains on the rise, with several states reporting cases. A common point of origin for all the positive horses is the National Cutting Horse Association’s (NCHA) Western National Championship competition, held April 28-May 8 in Ogden, Utah.

In California the number of EHV-1 positive horses has grown to six. According to Gary Magdesian, DVM, Dipl. ACVIM, ACVECC, associate professor in the department of medicine and epidemiology at the University of California, Davis (UC Davis), School of Veterinary Medicine, four horses at referral practices in Northern California tested positive for the virus May 16, and two horses currently in quarantine at UC Davis’ isolation facility tested positive the same day. Magdesian reported that veterinarians were treating the horses at UC Davis and that the animals were in stable condition as of Tuesday morning (May 17).

Magdesian emphasized that while the isolation facility at UC Davis is currently under quarantine, the general hospital at the William R. Pritchard Veterinary Teaching Hospital is not under quarantine and remains open: "The two horses with EHV-1 (at UC Davis) are under maximal isolation with no contact with the general hospital. All horses currently at the general hospital have tested negative for EHV-1. However, because of the external cases in the horse community, we have high level precautions in place to do everything possible to prevent a positive horse from entering our hospital.

"Due to reports of a number of additional febrile and neurological horses in the state of California, including Northern California, we are taking every precaution to prevent any positive horses from being admitted to the regular hospital and to protect all of our patients. We are testing all horses admitted to the hospital and using every infection control precaution to protect the hospital from being affected