Mosquitoes need water and heat to multiply, and this summer’s conditions could be perfect for a bumper crop of biting insects – some carrying deadly diseases – in the central San Joaquin Valley.
Public health and mosquito control officials are preparing for a surge of two species that can spread Zika and West Nile, two viruses that can cause severe illnesses. And the mosquitoes can spread other harmful viruses, including dengue fever, Saint Louis encephalitis and chikungunya.
Tim Phillips, manager of the Fresno Mosquito & Vector Control District, mobilized his crew of mosquito fighters in mid-March, the earliest assault ever to begin on green swimming pools, ponds and backyard bird baths where mosquitoes can breed.
By taking care of those mosquito breeding grounds, Phillips is hoping to have more time to answer telephone calls from itchy residents who he knows will have complaints, no matter how much his workers spray to knock out the pests.
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The mosquito that will generate the most calls – Aedes aegypti – is adept at hiding in backyards and evading insecticide spray. The mosquito has sent shudders through the medical community in the Valley, state and nation because the species can spread Zika, the virus that causes severe birth defects and neurological problems in adults.
They will bite, take off, come back
Tim Phillips, manager, Fresno Mosquito & Vector Control District
So far, no local mosquito has spread the Zika virus. But Fresno County had six Zika cases last year – five related to people traveling to Zika-infested countries – and one transmitted through sex. All it will take for a home-grown Valley mosquito to infect someone is for an infected traveler to return home and be bitten by a mosquito that then bites another person.
A voracious blood-eater, the Aedes mosquito attacks people in daylight, but mealtime can extend to after dusk, too. People in northern Fresno have swatted at the mosquito for two years now, Phillips says. “They’re really fed up with it.”
He calls the species “the cockroach of the mosquito world. They just come and never go away.”
The mosquitoes “don’t just bite and take a full meal. They will bite, take off, come back … and they’ll take multiple bites,” Phillips says.
The Aedes aegypti set up shop in the Valley about five years ago, first being identified in Madera and then Clovis, and from there spreading into Fresno. And now it’s extended its turf to Kerman, Firebaugh and Mendota, Phillips says.
Difficult to fight
So far, it has defied all eradication efforts, including some experimental ones.
The mosquito follows people inside homes and into cars. And listening to Phillips list the places the mosquito has been found breeding – saucers under potted plants, backyard water drains, poorly maintained home-humidifiers, coffeemaker water reservoirs, sink overflow drains, seldom flushed toilets – it’s easy to understand why it proliferates despite an intense public health campaign to annihilate it.
“It’s a real survivor,” Phillips says with grudging admiration to his voice. “All it needs is a little bit of water to develop, and people to bite – and it’s happy.”
But the Consolidated Mosquito Abatement District hopes sex will be the undoing of the Aedes aegypti.
Last year in a southeast Clovis neighborhood overridden by the mosquitoes, Consolidated workers released thousands of the male insects infected with Wolbachia, a bacterium-like organism. It was the first time in California that the Wolbachia-altered males had been released to mate with females, whose eggs then won’t hatch.
Consolidated Manager Steve Mulligan says that “we learned a great deal about how (the male mosquitoes) survived and dispersed following their introduction into this new habitat.”
The mosquito control district hopes to let more of these male bombshells fly this spring and summer. Consolidated worked with MosquitoMate, a Kentucky-based biotechnology company, for production of the male mosquitoes. This year it is in the process of adding a new partner, Debug, a Verily project, out of the Bay Area.
The sterile-insect technique shows promise, Mulligan says.
In addition, the public can expect to see more traditional spraying operations in neighborhoods where adult mosquitoes are in abundance, he says.
The Fresno County Department of Public Health got a $40,000 grant through the state to pay for a media campaign and outreach activities last year that focused on pregnant women and the general population. Some of the money paid for public service announcements aired in movie theaters and on the Big Fresno Fair’s “Jumbotron” television screens in October.
A proposed $163,000 grant will pay for a Zika registry and more outreach campaigns this year and in 2018.
A Zika website will be built that can automatically direct users to the mosquito control district that can respond to their complaints. “People don’t know what district they live in,” says Joe Prado, community health division manager. A Zika registry will be created to collect information about every Zika test ordered by a doctor. Whether testing finds the person positive or negative for the virus, there will be education provided about Zika and spraying around the home, if warranted, Prado says.
State health officials also are providing Zika outreach materials that the county can use, Prado says.
California got $18.6 million in federal funds for the Zika fight in 2016-17. So far, $8 million has been allocated to local health departments, vector control agencies and public health laboratories, the California Department of Public Health says. There is no additional Zika funding for 2017-18.
The Central California Blood Center has joined the health department to do outreach about Zika. Since the end of September, several states including California have tested every unit of blood for the presence of the virus. The Central California Blood Center ships blood samples to a testing laboratory in Phoenix, Arizona. Test results are available in two days, says Leslie Botos, director of community relations and development.
West Nile continues to be the most common mosquito-borne disease in California. And for most Californians the virus poses the greatest risk.
Dr. Vicki Kramer, California Department of Public Health Vector-Borne Disease Section
It’s difficult to know if Zika fears have affected blood donation, Botos says. “We do know that over the last few years it’s down 24 percent.”
The blood bank has tested donor blood for the presence of the West Nile virus for years, Botos says.
Jim Wasson, 74, of Fresno, says West Nile virus turned his life upside down three years ago.
Wasson was a practicing trial attorney when he became ill. He suspects a mosquito bit him either at his home or office. Testing found infected mosquitoes within a 5-mile radius of both locations.
His illness started with flu-like symptoms that progressed to a stiff neck and a high fever. When an arm became paralyzed, his wife thought he had had a stroke. But it was West Nile, which in less than 1 percent of the cases causes encephalitis or meningitis (inflammation of the brain or surrounding tissues) and other severe neurological illness.
Wasson says he was fortunate to walk again. But he has had to retire from practicing law. His hands shook too much to hold files in court. “I couldn’t take notes,” he says.
“Before, I jogged every day,” Wasson says. “I was very healthy. I did a lot of hiking, rode my motorcycle. Now it’s hard to explain … it’s like I aged 15 years.”
West Nile affects hundreds of people in California every year. In the past three years, more than 2,000 cases of the virus were reported. In 2016, the state had 442 cases and 19 deaths. Fresno County had 15 cases, Kings County had eight, Madera six and Tulare County 10, including one death.
“West Nile continues to be the most common mosquito-borne disease in California. And for most Californians the virus poses the greatest risk,” says Dr. Vicki Kramer, chief of the California Department of Public Health’s Vector-Borne Disease Section.
The Culex mosquito that spreads West Nile also can transmit the St. Louis encephalitis virus. Three cases were identified in 2016 in Fresno, Sacramento and Kern counties, the first statewide since 1997, she says.
Mosquito control districts mount yearly attacks on the Culex mosquito, which finds neglected backyard pools and ponds the perfect places to raise baby mosquitoes.
“They like standing water – typically fish ponds, ornamental ponds, bird baths, fountains that aren’t running all the time, pools and ponds,” Phillips says.
Reporting dead birds to the state also helps identify active areas of West Nile virus, Kramer says.
Widespread problem expected
This year, the Culex mosquito could be widespread.
“With the rivers running high, we could have additional mosquito production in areas along the rivers where we haven’t had issues in the past few years because of the drought,” says Mulligan of Consolidated.
But the Aedes aegypti mosquito continues to dominate the discussion in California. And for good reason. As of April 14, there were 533 travel-associated cases reported.
In Fresno County, in addition to the five travel-associated Zika cases in 2016, the county had seven travel-associated cases of dengue fever and three travel-associated cases of chikungunya. The tropical diseases have symptoms that include fever, severe headaches and body aches.
It’s essential to control the Culex and Aedes aegypti mosquitoes, health and mosquito control officials say. People need to dump any backyard containers that are holding standing water, and since the introduction of the Aedes mosquito, Phillips says the smallest containers around a home could be breeding sites.
Wearing mosquito repellent also should become commonplace.
Dr. Ken Bird, the health officer for Fresno County, says it’s important for people to protect themselves from mosquito bites when traveling and at home. Pregnant women should seriously consider the risk for any travel to areas that have ongoing Zika transmission, Bird says. Virtually all of Mexico, for example, is considered such an area, he says.
There’s no going back to pre-Zika days, Phillips says. “This mosquito is going to change the way we live in California. I’m quite sure of that.”
Stopping mosquito bites
Before going outdoors apply insect repellent containing EPA-registered ingredients, including DEET, picaradin, oil of lemon eucalyptus, or IR3535, according to label instructions.
Dress in long sleeves and pants.
Install screens on windows and doors and keep them in good repair.
Eliminate all sources of standing water, including flower pots, old tires and buckets.
If you are bitten by mosquitoes, contact your mosquito control district.
Source: Mosquito and Vector Control Association of California
To report mosquito problems
Tulare Mosquito Abatement District: 559-686-6628; web site unavailable.