Officials raise alarm on early mosquito hatch in North Bay

Aggressive and potentially disease-carrying mosquitoes are hatching ahead of schedule and in greater numbers in Sonoma and Marin counties, prompting officials to issue early pleas for the public to take precautions against getting bit.

That was the message the Marin-Sonoma Mosquito and Vector Control District conveyed Friday in a news release, simultaneous to the district mailing out ballots to more than 200,000 property owners in the two counties seeking a new tax to help fund the agency’s services and employee costs.

Phil Smith, the district’s general manager, called it a “fair question” to ask whether the district is being overly alarmist to try and gain support for the tax levy. He made the case that the relatively low prevalence of mosquito-borne illnesses such as West Nile in the two counties is due in part to the district’s work.

“We’ve worked to minimize the risk to our residents. That isn’t a cause for complacency,” he said.

A top California health official agreed Wednesday.

“We do know that the best defense against West Nile virus is mosquito control,” said Dr. Vicki Kramer, chief of the Vector-Borne Disease Section of the California Department of Public Health.

West Nile outbreaks in people living on the North Coast remain relatively rare, with only eight reported cases in Marin, Sonoma, Lake and Mendocino counties in the past eight years. The only reported human case in Sonoma County was in 2007.

But Kramer said for every documented case, there are dozens more that are never reported, due in part to the fact that upward of 80 percent of those infected with the virus never show symptoms.

“As with most infectious diseases, West Nile is underreported,” she said. “Because West Nile is a serious disease and can be fatal, I think it’s particularly important to recognize the risk of exposure, particularly in summer months.”

Officials with the local vector control district say they’ve detected larvae of the mosquito that carries West Nile virus about a month ahead of schedule, possibly signaling the earlier arrival of the disease in the two counties. Last year, adult mosquitoes carrying the virus were first detected in May.

Officials attribute the early outbreak to a variety of factors, including the North Coast’s lingering drought and a warm winter punctuated by periods of heavy rain. In marshes, higher concentrations of mosquitoes are finding refuge in fewer pools of water, which also attract birds, which can infect mosquitoes with West Nile virus, and vice versa.

One in five people infected with the virus will develop symptoms similar to the flu, including fever and headache, body aches, joint pains, vomiting, diarrhea or rash, according to the Centers for Disease Control and Prevention. But something under 1 percent of patients develop severe neurologic conditions that may include encephalitis or meningitis. About 10 percent of those with neurologic infection will die, the CDC said.

Statewide, there were 798 reported human cases of West Nile virus in California in 2014, resulting in 29 deaths. That’s more than double the number of cases reported the previous year, during which 15 people succumbed to the disease.

On Monday, Nick Picinich, a technician with the vector control district, trudged into the Petaluma marsh near Highway 101 wearing waders to collect samples from standing pools of water. He didn’t have to hunt hard for larvae of a saltwater marsh mosquito that can fly up to 20 miles and delivers a painful bite.

“It’s very aggressive,” Picinich said.

Officials also are monitoring for signs of mosquitoes that have already been detected in several counties in California and are capable of transmitting a range of viruses, including those that cause dengue fever, chikungunya and yellow fever.

Technicians were planning to return to the Petaluma marsh this week to begin treating the water with a biological control agent.

Officials are urging the public to take steps to minimize mosquito outbreaks. These include eliminating standing water in old tires, buckets, toys or other items, covering rain barrels with mosquito-proof screens and cleaning out gutters to allow water to flow. People should also wear mosquito repellent when they are outdoors at dusk or dawn.

Problems can be reported at www.mosquito.com or by calling 800-231-3236.

You can reach Staff Writer Derek Moore at 521-5336 or derek.moore@pressdemocrat.com. On Twitter @deadlinederek.