LAKE COUNTY >> Lake County has reported its first probable case of West Nile Virus and is investigating a second, serving as a reminder that this mosquito-borne disease is present and circulating.
“Even though our attention has been dominated by recent wildfires, we should not forget that West Nile Virus season is in full force” said Lake County Health Officer, Dr. Karen Tait. “Since there is no specific treatment once the infection develops, the best prevention is to avoid exposure through mosquito bites.”
West Nile Virus infection can range from mild, even symptom-free infections, to deadly forms of the disease. Mild forms of the infection often go undetected. Less than 1 percent of cases result in severe illness and these are the most likely to be diagnosed. People over age 50 and diabetics are at risk for the more severe forms of the disease.
Local surveillance is a joint effort of Lake County Vector Control District (LCVCD) and Lake County Public Health. Typically, before human cases occur, the infection first appears in mosquito pools, followed by wild birds and sentinel chicken flocks selected for regular testing. This pattern was the case this year, with the West Nile virus first noted in mosquitoes on July 9, a positive wild bird on July 24, and a positive sentinel chicken flock on July 27.
The first human case reported this year in Lake County became ill during the third week of July. The second probable case that remains under investigation became ill in mid-August. Both individuals experienced the “neuroinvasive” form of the infection, which can produce symptoms ranging from a form of meningitis to more severe and potentially permanent effects on the nervous system.
Fortunately, both Lake County residents are making a good recovery.
Lake County Public Health and Lake County Vector Control District (LCVCD) have a strong partnership for control of West Nile and other vector-borne diseases. When Public Health receives a report of a suspected case, LCVCD is immediately informed and takes action to increase surveillance and reduce mosquitoes in the location(s) where the individual was likely to have been exposed. “Even though we cannot always prevent a first case of WNV, we have tools at our disposal to reduce the chance of additional cases in the same neighborhood,” said Tait.
Dr. Jamesina Scott, District Manager and Research Director of LCVCD, notes that the steps in response to reported virus activity include searching for sources of standing water where mosquitoes develop, which are often in the form of neglected ponds and swimming pools.
“We’re fortunate to have a close partnership with Public Health,” said Scott. “When there is a suspected West Nile virus case, we are able to respond quickly to reduce the risk of additional human cases.”
“With the drought, we’re seeing more swimming pools being taken out of service. When a pool isn’t being chlorinated or filtered, it becomes the perfect home for mosquitoes,” Scott explained. “We offer free mosquito-eating fish for use in unmaintained swimming pools—they eat the immature mosquitoes before they grow into flying, biting adult mosquitoes,” said Scott.
Since 2004, six people in Lake County have been diagnosed with West Nile virus. For 2015, West Nile virus has been detected in 20 mosquito samples, three dead birds, and two sentinel chickens in Lake County.
So far this year in California, 57 human cases, including 2 fatalities, have been reported from 13 counties. More than one-third of the cases were reported in the past week.
In recent years, Lake County reported one case in 2012 and another in 2014.
West Nile has been reported in several Northern California counties, including the Bay Area. A portion of San Jose and Santa Clara will be fogged Thursday night after adult mosquitoes tested positive for West Nile virus, the Santa Clara County Vector Control District announced.
The is one reported case from Mendocino County, eight in Glenn County and 30 in Butte County.
The San Jose Mercury News contributed to this report
