A crow found in Vallejo has tested positive for West Nile virus, according to officials from the Solano County Mosquito Abatement District and Solano County Department of Health and Social Services.

“This is the first evidence that we have of local WNV activity in Solano County this year,” said Dr. Michael Stacey, Solano County chief medical officer and deputy health officer.

“We have not had any reported cases of WNV infection in humans so far this year.”

Stacey said the state Department of Public Health reported that West Nile had been found in nine other counties, but that no cases in humans have been detected so far this year.

That department’s records showed 801 human cases of West Nile virus were reported in 2014, the second-highest number of human infections since the virus first was identified in California in 2003.

In addition, a majority of the birds tested in 2014 for West Nile virus had positive results, which also was unusual, he said.

Mosquitos breed in still water, but ironically the severe drought in California has contributed to high West Nile activity, Stacey said — because there are reduced sources of water for both birds and mosquitos, and that allows them to come into closer contact with each other.

Jon Blegen, Solano County Mosquito Abatement District manager, concurred with Stacey.

“The ongoing drought may contribute to a continued elevation of West Nile activity this year,” Blegen said.

Stacey wouldn’t predict if West Nile virus cases would exceed those of last year. “There are many factors that contribute to the level of activity, including climate, the number and types of birds and mosquitoes in an area and the level of immunity to WNV in birds,” he said.

West Nile virus is transmitted to humans and animals through the bite of an infected mosquito, he said. Mosquitoes become infected when they feed on infected birds.

“This serves as a reminder to the community that we need to follow … simple precautions to ensure that we protect ourselves against mosquito bites and reduce our risk of infection,” Stacey said.

County officials have recommended residents avoid being outside at dawn and at dusk.

“Mosquitoes are most active in the early morning and evening,” Stacey said. “Residents should avoid being outside at these times. If you are outdoors, wear long-sleeved shirts and long pants and use insect repellent.”

Residents should drain any standing water and remove the objects that have been collecting the water.

“Mosquitoes lay their eggs on standing water,” Stacey said. They can be discouraged by draining empty flower pots, buckets, barrels, old car tires, rain gutters and pet bowls.

Those who have ornamental ponds may get free mosquito fish by calling the Solano County Mosquito Abatement District, 707-437-1116.

Insect repellents keep mosquitoes from biting, Stacey said. Those going outside should apply an insect repellent registered with the Environmental Protection Agency — such as those with DEET, picaradin, oil of lemon eucalyptus or IR3535 — and use them according to the manufacturer’s instructions, he said.

Residents also should ensure that their doors and windows have tight-fitting screens to keep mosquitoes out, Stacey said, and should repair or replace screens if they have tears or holes.

Blegen said Solano County is using “all the tools that we have in order to control the mosquito populations.”

But he pointed out mosquito repellents are readily available, and he encouraged their use on a regular basis.

“I also would like to ask residents to help with prevention and control efforts by making sure that they don’t have any standing water on their property and to report any unmaintained swimming pools and stagnant water by calling 707-437-1116.”

Many who become infected with West Nile virus will not develop any symptoms, Stacey said.

“About 1 in 5 will develop mild symptoms including fever, headache, body aches, nausea, vomiting and swollen lymph glands,” he said. “However, less than 1 percent, or about 1 in 150, of persons with WNV infections will develop severe neurological disease. In very rare occasions, WNV can be fatal.”

While anyone can become infected with West Nile virus, those who are 50 or older and those with diabetes or hypertension are at higher risk of developing severe illness and complications, he said.

Anyone who sees a dead bird or squirrel may report them online at www.westnile.ca.gov or may call 877-WNV-BIRD (877-968-2473).