In spite of the additional positives, the lack of clinical signs of the virus in the affected horses is good news, said Dr. David Wilson, director of the Large Animal Clinic at the University of California-Davis, which is handling the sample taking and tests. Golden Gate Fields, Bay Meadows and the Alameda County Fair Grounds in Pleasanton are under quarantine restrictions imposed Dec. 29 by the California Horse Racing Board.
"If we can get another five or six days without any more clinical cases, we'd feel pretty good about that," Wilson said when asked about a possible time frame for the end of quarantine. "We are monitoring the shedding of the virus and if everything goes well, I would think three weeks or so." He noted that the CHRB would make the final determination.
Asked if he thought Northern California horses would be able to travel to Santa Anita to compete in Sunshine Millions on Jan. 27, Wilson responded, "That would not be entirely out of the question."
Under the current restrictions, horses may ship between the three quarantined tracks but nowhere else.
Wilson said one of the horses from Mason's barn that tested positive had recently returned from Santa Anita, so additional testing is being done in the barn area at the Southern California track where the horse had contact with others. In addition, UC Davis is running samples taken Jan. 2 from 26 horses, including stable ponies, in barns adjacent to Mason's to be sure the infectious virus hasn't spread. No horses outside of Mason's barn have tested positive.
While not showing clinical signs of EHV-1, the five horses have been segregated from the rest of Mason's 40-horse string, said Dr. Rick Arthur, the CHRB's equine medical director.
He said a swab test of the horses' nostrils revealed the presence of the EHV-1 strain in their mucus membranes, "otherwise you would have no idea there was anything wrong with them," he said.
"It does not appear to be the same virulent strain of equine herpesvirus that we saw previously in New Jersey," Arthur added. "These cases are not showing the same neurological symptoms associated" with last summer's outbreak.
Arthur said he would have expected to see signs of respiratory infection or fever, but that such symptoms were absent. EHV-1 has proven fatal in the most severe cases.
Meanwhile, the only Thoroughbred in California to show neurogenic signs of the disease is responding well to treatment and could be released from an isolation unit at UC Davis' equine medical facility within a few days, Wilson said.
The 3-year-old gelding Royal Brass, transferred to Davis last week after losing his coordination and dribbling urine, was the first Thoroughbred at a California track to test positive for EHV-1. Wilson said an anti-viral drug used on humans with herpes simplex, valcyclovir, has Royal Brass nearly back to normal. "They used valcyclovir during the scare at Monmouth Park last summer," he said. "He's got his bladder function back and he's really turned around."
Mason's horses began working out again this week. They are allowed on the track after 10 a.m, when all other horses have completed training.