West Nile Virus Detected In Napa County

NAPA COUNTY, CA — The presence of West Nile Virus in mosquitoes in Napa County has been confirmed by authorities with Napa County Public Health and the Napa County Mosquito Abatement District, county officials said late Friday.

The positive specimen sample was collected July 19 in Calistoga.

As of Friday, there were no human cases of WNV reported by the Napa County Public Health Division.

The virus is transmitted to mosquitoes when they feed on infected birds. Both humans and animals can contract WNV if bitten by an infected mosquito. Therefore, Napa County Public Health recommends people take preventive measures (see below) to avoid mosquito bites — not only in Napa County but in regions across California.

Thus far this year in California, eight human cases from five counties have tested positive for the virus — six of which were reported this week. Of the eight cases, one was in San Joaquin County, one was in Merced County, two were in Tulare County, one was in Kern County and two were in San Bernardino County.

Two horses from two California counties and 27 sentinel chickens from four counties have tested positive for WNV this year.

As of Friday, 181 dead birds from 20 counties have tested positive for the virus across California, while there have been 1,582 positive mosquito samples reported from 27 counties, according to Westnile.ca.gov. At this time last year, there were 965 positive mosquito samples reported in the Golden State.

In nearby Contra Costa County, the Contra Costa Mosquito and Vector Control District reported its third dead bird of the year Friday and its third group of trapped mosquitoes this year that tested positive for WNV. The dead bird was a California scrub jay, collected from Oakley, while the mosquitoes were trapped in Brentwood. Last month, two groups of trapped mosquitoes from Discovery Bay and two dead birds; one from Brentwood and the other from Martinez, also tested positive for WNV in Contra Costa County.

"Statistically, this is the time of year when we typically see the highest risk of human cases, so it is very important for Contra Costa County residents who plan to be outside when mosquitoes are present, to wear an EPA-registered insect repellent that includes one of the four most effective active ingredients: DEET, Picaridin, IR3535, or the repellent version of Oil of Lemon Eucalyptus. And always follow the instructions on the label when using insect repellent," said Steve Schutz, scientific program manager for the Contra Costa Mosquito and Vector Control District.

Most people —about four of five — infected with the West Nile virus will not develop any symptoms. About one in five will develop mild flu-like symptoms, including fever, headache, body aches, nausea, vomiting, and swollen lymph glands. However, about one in every 150 people infected with WNV will develop severe neurological disease. In rare cases, WNV infection can be fatal.

Anyone can be infected with WNV but those at greater risk of developing severe illness include people 60 or older, people who have received organ transplants, and people with certain medical conditions such as cancer, diabetes, hypertension, and kidney disease.

Preventive Measures

With the presence of WNV confirmed in Napa County, officials on Friday advised taking the following preventative measures:

Protect yourself at dawn and dusk: Mosquitoes are most active in the early morning and evening. Avoid being outside at these times. If you are outdoors, wear a long-sleeved shirt and long pants, and use insect repellent.

Drain standing water: Mosquitoes lay their eggs on standing water. Eliminate all sources of standing water on your property and drain empty flowerpots, buckets, barrels, old car tires, rain gutters, and pet bowls.

Use DEET and other repellents: Insect repellents help keep mosquitoes from biting. Apply an EPA-registered insect repellent containing DEET, picaridin, oil of lemon eucalyptus, IR3535, or para-menthane-diol products per the manufacturer's instructions.

Check doors and windows: Ensure that doors and windows have tight-fitting screens to keep mosquitoes out. Repair or replace screens with tears or holes.

Napa County plans to continue coordinated surveillance with neighboring mosquito abatement districts and the California Department of Public Health — testing birds and mosquito populations for the virus.

Napa County residents are encouraged to report dead birds online at Westnile.ca.gov or by calling 1-877-WNVBIRD (1-877-968-2473). For questions about local mosquito surveillance and problems with mosquito control, residents can call the Napa County Mosquito Abatement District at 707-553-9610.