Mosquitoes carrying West Nile virus have been detected for the first time this season across Sacramento and Yolo counties, authorities said Friday. The finding means all 1.5 million residents of both counties may be considered equally at risk of being infected by mosquito bites.
David Brown, general manager of the Sacramento-Yolo Mosquito and Vector Control District, said the district is considering mailing notices to all residents calling for extra vigilance.
"Our intent is to let everybody know: We've got a problem," Brown said. "If you've ignored (the risk) to date, quit ignoring it."
To reduce the chances of infection, residents are advised to eliminate unnecessary sources of standing water, where mosquitoes breed, and use mosquito repellent when outdoors, especially during dawn and dusk, when the biting insects are most active.
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West Nile virus is mostly a disease of birds that is transmitted by mosquitoes. The virus also can sicken humans and horses.
Based upon recent reports of dead birds, mosquito district officials suspected they'd soon find infected mosquitoes in at least some parts of the county. But the test results that came back Friday showed the virus more widespread than anticipated.
"I've got one (positive sample) in the Citrus Heights area and one in the Freeport area," Brown said. "In Yolo, I have one in Knights Landing and one in Winters. So my point is, we've got the north part of Sacramento County and the south part of Sacramento County, the north part of Yolo County and the south part of Yolo County. I'm sure we've got virus in between."
Virus-carrying mosquitoes were found in Sacramento County last summer also, but they were in smaller numbers and turned up later in the season, Brown said.
"There were nowhere near as many and certainly not as widespread," he said.
West Nile virus was first detected in this country in New York in 1999. The virus has since spread from coast to coast.
Most people who are infected will have no symptoms. A few will feel like they have a flu, with a fever, aches and fatigue. About one in 150 will come down with grave, potentially fatal neurological problems, including meningitis and encephalitis.
So far this year, two Californians have been sickened by West Nile virus, one in Tulare County and the other in Riverside County.
Nationwide, 13 human cases had been confirmed as of July 5, the latest date for which the national Centers for Disease Control and Prevention has a tally.
Birds are harbingers of the disease. In particular, corvids - crows, magpies and jays - are especially sensitive to West Nile virus. Corvids tend to develop high levels of virus in their bodies and die quickly.
In Orangevale, Ron Throp reported an eerie drop-off in the number of magpies that usually flock near his home.
"The last few weeks, we've seen several of them dying," Throp said Friday. "They would just kind of sit on the lawn or sit out in the street, and cats would even kind of leave them alone. And they would just hop around, they wouldn't fly very much and pretty soon they were dead."
Throp said he and his wife take a 2 1/2 mile walk around Orangevale and Citrus Heights each day and have noticed that the magpies they once saw regularly on that long walk have all but disappeared.
While the Sacramento-Yolo mosquito district did not identify a spike in dead birds in Throp's area, district officials last week sent postcards to 98,437 addresses in and around Carmichael, Arden and Rancho Cordova, alerting residents that a significant number of dead birds had been found in the area, suggesting a West Nile virus hot spot.
Brown said that while the district had been receiving 200 to 300 calls each week about dead birds, people in that 4-square-mile area reported about 50 dead corvids in the space of a week.
The district stepped up its testing of mosquitoes from that area, expecting to find the virus in the bugs themselves. The results Friday showed that the virus was indeed in that area - as well as elsewhere in the county.
West Nile prevention tips
To reduce the risk of catching West Nile virus, the Sacramento-Yolo Mosquito and Vector Control District recommends:
Use an effective mosquito repellent containing ingredients such as DEET, Picaridin or oil of lemon eucalyptus.
Repair holes or tears in door and window screens.
Drain standing water.
Wear long pants and long sleeves outdoors when practical.
Avoid being outside at dawn and dusk when mosquitoes are most active.
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- The Bee's Edie Lau can be reached at (916) 321-1098 or email@example.com.