West Nile Virus activity wanes as temperatures drop, but the Marin/Sonoma Mosquito and Vector Control District announced this week that five more infected birds—one in San Rafael—tested positive.
That brings a total of five WNV-positive birds in Marin County this year - in San Rafael, Novato, Ross, Corte Madera and Greenbrae - but the number isn’t expected to rise by much this year.
“During the summer is when WNV transmission is most likely to occur due to the abundance of vector mosquitoes as well as the warmer weather,” said Nizza Sequeira, the district’s public relations director. “We actually do have mosquitoes year round in both Marin and Sonoma counties but they are most abundant during the spring and summer months and begin to taper off into fall.”
That’s not to say all mosquito activity comes to a halt.
“As we enter the cooler months mosquitoes are not as active but will continue to reproduce,” said Sequeira. “For example, we will see more of what we call the cool-weather mosquito (Culiseta incidens) and the large winter mosquito (Culiseta inornata).”
While all five of this week’s birds tested positive for WNV, lab results confirmed that only two had been recently infected with the virus, both in Santa Rosa. Four of the five birds were found in Santa Rosa.
“As for virus activity in Marin and Sonoma counties, it was mild compared to other parts of California as well as the rest of the nation,” Sequeira said. “Historically, this area has not experienced as much virus activity in comparison to areas where the temperatures are much higher.”
Sequeira said WNV is “a serious threat to human health, but it can be prevented."
With wintertime just around the corner, the district urges residents to get a jump-start on spring-cleaning before the rains begin.
“One way to help reduce mosquitoes and lessen the risk of West Nile virus is to remove items around your property before they have a chance to fill up with rainwater,” Sequeira said.
One of the most common areas District officials find mosquito production is in residents' backyards. Removing items now, before they have a chance to collect rainwater, can help reduce problems next season. A backyard checklist is available at msmosquito.com to help residents identify areas that are often overlooked. Residents are reminded that mosquitoes are present year-round in both counties and to report problems or suspected areas right away, even in the wintertime.
West Nile virus (WNV) is a mosquito-borne disease that is spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread the disease to humans and other animals.
Fewer than one percent of people (1 in 150) infected with West Nile Virus develop serious illness. These cases may last for extended periods of time, result in permanent neurological damage and may be fatal. Approximately 20 percent of people (about 1 in 5) infected with West Nile Virus experience mild symptoms that may include fever, headache, body aches, nausea, rashes, swollen lymph nodes and vomiting. Approximately 80 percent of people (about 4 out of 5) infected with West Nile Virus do not show any symptoms.
For more information or to report mosquito problems contact the Marin/Sonoma Mosquito and Vector Control District at 1-800-231-3236 or visit www.msmosquito.com.
Report dead birds to the West Nile Virus Hotline at 1-877-968-2473, or online at www.westnile.ca.gov.