Updated Sept. 16 to reflect revised information from the California Department of FOod and Agriculture.

Eight additional horses in Tuolumne County, Calif., are exhibiting clinical signs consistent with equine herpesvirus-1 (EHV-1) after a mare in that county tested positive for the neurologic form of the virus on Sept. 12, according to a statement from the California Department of Food and Agriculture (CDFA). The exact clinical signs each horse are displayed were not reported.

The initial confirmed positive mare, who was being treated at a referral hospital, has shown improvement and was returned to her quarantined premises in Tuolumne County for recovery, the statement said.

"Epidemiologic investigation is ongoing and the premises owner and CDFA has contacted potentially exposed horse owners that visited the affected premises over the past two weeks," the release read. "On Sept. 13 University of California, Davis, veterinary school staff collected samples (blood and nasal swabs) from 150 animals on the premises, including the eight demonstrating compatible clinical signs. Test results are anticipated within the next few days