John Lindblom–Record-Bee staff
LAKE COUNTY — Despite the fact that two people in Lake Coun-ty have tested pos-itive for the West Nile virus this year, there have been encouraging signs, both locally and statewide, that spark hopes that the virus is dissipating.
In Lake County, WNV”s effect on horses has been significantly decreased, according to Art Colwell, general manager of the county”s Vector Control Unit. Colwell said there have been only two confirmed horse cases, compared to 10 in 2005 and four in 2004.
“It had a lot to do with the fact that there”s a vaccine for the horses,” Colwell said. “I would say that it”s encouraging ? if it is indicative that horses are getting vaccine and getting their booster shots.
“If you look at the overall situation we are down in most of the categories from last year and that is also true on a statewide basis,” Colwell added.
Across the state there have indeed been noteworthy developments suggesting California is bringing WNV into check.
The most important one is the decline in human deaths. Only three deaths have been attributed to WNV in California this year. In 2004 and 2005, 47 deaths were caused by the virus, according to information provided by the state.
The human case count (224 in 32 counties) is four times lower than last year.
But California”s milder year, however, so far is only an anachronism, because nationwide the WNV case count appears headed for a likely increase over 2005”s totals, according to the Washington (D.C.) Times.
Nevertheless, other favorable signs of a declining presence of WNV in Lake County this year are Vector Control”s identification of only one new positive mosquito pool in September, bringing the total for the year to an even dozen. This compares to the five positive pools in September of last year and 13 in September, 2004.
The WNV dead-bird count for the county is only six for the year with one positive case in September. This compares with 11 dead birds testing positive in September last year and 14 in 2004.
“What happens is that the birds are the primary reservoirs. If most of the birds get killed off because of this virus and the only ones who survive are immune then you can expect there will be a decrease in virus activity because you have fewer hosts to accommodate them,” Colwell said.
Although temperatures in the county have dropped appreciably in recent weeks, Colwell said that mosquitoes carrying the WNV are still present this year.
“Mosquito densities are decreasing,” he said, as noted by the infection rates in mosquito pools, “but we had positive indicators in October in both 2004 and 2005.”
How late?
“This is largely temperature-dependent,” Colwell said. “If it gets too cold, it inhibits the development of the virus in mosquitoes. But if there is warm weather throughout October, people should continue to take precautions.”
Contact John Lindblom at jlwordsmith@mchsi.com
