California, whose horse population has been hit by West Nile virus harder than any other state in the nation this season, has about one month to go before it can expect a decline in the number of cases.
Dr. Gregory Ferraro, director of the center for equine health at the University of California-Davis, said there have been 168 equine cases in the state confirmed by the California Department of Food and Agriculture as of Aug. 30, with 78 resulting in death or euthanasia.
"Of those (168) cases, 110 horses were not vaccinated and 48 had incomplete or partial vaccinations, where they may have had the initial shots but missed follow-ups," Ferraro said. "That tells you that vaccination works."
Ferraro said September figures to be an active month, but that once the mosquito season begins to slow in October, so too should the virus, which has sped through the state and the rest of the nation's western region rapidly this summer.
There has been one racetrack incident reported so far. It resulted in the death of the 5-year-old mare Quick Nip, who was euthanized Aug.10 at Golden Gate Fields after contracting the disease at an unknown location.
"It seems like she was partially vaccinated," Ferraro said. "It was a situation where she had gone through three ownerships and one guy thought the other guy had taken care of it. No one is quite sure."
He said that of the 78 horses that have died, 56 had never been vaccinated and 16 had received incomplete inoculation.
The latest data also showed that of the dead horses, 59 were euthanized
"What we're seeing is that the ones who were euthanized had owners who were at the lower end of the economic scale. So when the horse is diagnosed with the disease, they choose euthanasia over treatment," Ferraro said.
"Because we've had three to four years to get ready for this, we've had pretty close to an 80% vaccination rate," he said. "But in a state with 1.2 million horses, there's still a significant number who aren't. The other thing that concerns us is that the pattern across the country has been for the virus to show up for a two-year cycle. We've only had the one year and data shows that the second year is the worst."