By Hilary Corrigan
Triplicate staff writer
A horse tested positive for West Nile Virus this week, marking the first reported case of the disease in a mammal in Del Norte County.
But the virus most likely already has infected people and horses who showed no signs or recovered without knowing they contracted it, said Dr. Thomas Martinelli, public health officer for the county's department of health and social services.
Common to Africa, West Asia and the Middle East, the mosquito-borne virus first showed up in America in New York in 1999, spreading across the country.
It first appeared in California in 2002 in a human. By 2004, it had reached all of the state's 58 counties.
Until now, the only confirmed cases in Del Norte County had shown up in birds two in Crescent City and one in Gasquet, all in 2004, according to state data.
"I'm kind of surprised it's taken this long," said Dr. John Jacobson, a veterinarian at Town and Country Animal Clinic in Brookings who treats the region's horses and watched last summer as cases mounted in Idaho and eastern Oregon. "We kept expecting it to show up."
Jacobson also has watched the trends in other horse populations. When the virus first reaches an area, it tends to cause an initial rush of cases with a high number of deaths.
"We expect to have a lot more problems," Jacobson said of the coming summer. "2007 will be probably the worst year that we have here."
Then the cases tend to drop off as more horses receive vaccinations and build up their own natural immunity to the established virus.
"It always makes news when it first hits, but the reality is, it's here and it's going to be here," Jacobson said. "It's just something we're going to have to live with."
Won't release location
Martinelli declined to release the location in Del Norte County that the infected horse came from, saying that such information would spark public concern and fears about grazing lands.
"All that's going to do is create hysteria," Martinelli said, noting that the horse was probably infected months ago. "It's just an isolated case."
The disease harms horses and certain birds more than other mammals. Cattle and bears, for instance, tend to brush it off.
The effect on people varies, but about 80 percent of those infected show no symptoms, according to the Centers for Disease Control and Prevention. Some suffer fever, aches, nausea and swollen glands. About one in 150 suffer extreme sickness high fever, headache, coma, paralysis, vision loss and neurological problems.
In horses, the virus attacks the nervous system and can cause lack of appetite, depression, fever, paralysis, muscle twitching, convulsions, coma and death.
Horses have some help in the form of an annual vaccine that costs about $30.
While it does not guarantee prevention of West Nile Virus, it's still worthwhile, Jacobson said.
"It's the only protection you have," he said.
About 1,500 horses live in Del Norte and Curry counties, mostly belonging to recreational riders.
Dr. Dennis Wood, a veterinarian who operates All Creatures Animal Hospital and Bird Clinic in Crescent City, gets his own two horses vaccinated each year to block the disease.
He expects the county's confirmed case to prompt other horse owners to do the same.
"It'll certainly be easier to get people to listen now," Wood said, noting horse owners who balk at the extra chore and expense and point to a lack of local cases. "I think people tend to be a little more responsive when it's in your own backyard."
During the last two years, Jacobson has incorporated West Nile Virus vaccines into routine horse care, administering the shots along with those for tetanus and encephalitis.
"Essentially now it's affected the entire United States. We're kind of the last," Jacobson said. "It's going to always be with us from now on."
West Nile Facts
Mosquito-borne disease common to Africa, West Asia, the Middle East and now, North America
The disease does not spread from mammal to mammal, but by mosquitoes that carry it after feeding on infected animals
Prevent the disease by avoiding mosquito bites wear long sleeves and long pants, install screens on windows and rid areas of standing water in pots or buckets
Sources: Centers for Disease Control and Prevention and California West Nile Virus Web site