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Mosquito abatement front line of West Nile prevention
Monica Patterson, a vector biologist with the Turlock Mosquito Abatement District, sets a trap using carbon dioxide, which attracts the mosquitoes. Trapping is a key part in identifying disease activity in the mosquito population. - photo by SABRA STAFFORD / The Journal

It is early morning when the truck turns onto the quiet road. As the denizens doze the truck emits out a fine mist targeting the smallest of an enemy that carries a huge potential for danger.

This is the battle ground in the fight against West Nile Virus and other diseases like Dengue and Yellow Fever that mosquitoes can spread to the population and the Turlock Mosquito Abatement District is on the frontline of the defense.

The Turlock Mosquito Abatement District is responsible for keeping the mosquito population in check in a region that covers a 1,000 square mile area from La Grange to Newman. It takes a two-prong approach to control efforts, the first of which targets the breeding grounds, and the second aims to reduce the adult population.

“Mosquito control is one of those things you have to get out in front of, because if you wait until you’re seeing them, then it’s too late,” said Turlock Mosquito Abatement District General Manager David Heft.

Most often, West Nile Virus is spread by the bite of an infected mosquito. Mosquitoes become infected when they feed on infected birds. Infected mosquitoes can then spread West Nile Virus to humans and other animals when they bite, according to the Centers for Disease Control.

Approximately 1 in 5 people who are infected with West Nile virus will develop symptoms such as fever, headache, body aches, joint pains, vomiting, diarrhea, or rash. Less than 1 percent will develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues). About 10 percent of people who develop neurologic infection due to West Nile virus will die, according to the CDC.  People over 50 years of age and those with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and organ transplants, are at greater risk for serious illness.

A recent report from the CDC indicates that for every one diagnosed case of West Nile Virus another 150 people have the disease and are either undiagnosed or misdiagnosed.

“It’s quite a bit more active than what people think,” Heft said.

West Nile Virus typically starts to appear in April or May and will continue to have a presence through October. The weather can also be a significant factor in West Nile virus outbreaks. The CDC reported higher number of cases during periods of abnormally high temperatures.

“The virus has been more active in recent years, especially at the end of the season,” said Monica Patterson, a vector biologist with the District.

The most recent report from the California Department of Public Health shows Stanislaus County has four confirmed human cases of West Nile Virus. Thirteen dead birds have tested positive for the virus, as have 65 mosquito samples. Within the state there have been five fatalities this year from West Nile Virus.

Mosquitoes like to breed in stagnant water, preferring weedy areas that provide cover. The lagoons at dairy farms make for perfect breeding grounds, but so do flooded fields, uncared for swimming pools, urban catch basins, overwatered lawns, and pretty much anything that holds water and allows it to stagnate.

The District doesn’t get notices of irrigation, so it relies on the nine full-time operators to keep an eye on any potential problems. And it doesn’t take long for a problem to arise.

“A mosquito can go from egg to adult in three to four days,” said Heft. "So if a farmer irrigates on Thursday and we don’t know about it, by Monday we’re getting calls about mosquitoes.”

There is a pesticide that target the adult mosquitoes and another that kills the larva. The District uses truck spraying and chemical pellets for a more precise targeting, but sometimes bigger efforts are necessary.

“Killing the adults is just a Band-Aid,” Heft said. “We have to get at the eggs and the larva to really make an impact.”

Some species are proving to be resistant to the chemical released off the trucks, so the District has turned to another chemical that has to be done through aerial spraying. The aerial spraying can also cover large swaths of land at a time, around 60,000 acres. The district does post spray notices on their website.

“It has an ultra low volume,” Heft said. “It’s less than an ounce an acre and is atomized into microscopic parts. California has very stringent laws about the chemicals we use and this is very safe for people and mammals.”

A big part of the district’s operations is trapping the mosquitoes and testing them for any potential disease activity. There are an estimated 3,500 mosquito species in the world, and about 25 that are known to live in Stanislaus County. Of those, two are known to carry the West Nile Virus in this area.

The trapped mosquitoes are put into a hibernation state, sorted by species, entered into a state database and then sent off for virus testing.

Outside of chemical treatments, the District does provide mosquito fish for pools that have gone green and are attracting mosquitoes.

“West Nile Virus has only been here for 10 years,” Heft said. “We still don’t have all the answers about controlling it – not even close. Awareness is a big part of our effort. If people let us know about their irrigation, or pool, or just an area where there are a lot of mosquitoes, it helps us a lot.”

The most effective way for individuals to prevent exposure to mosquito bites and West Nile virus is to remember the “Three D’s”:

1. DEFEND – Use an EPA-registered insect repellent with DEET, picaridin, oil of lemon eucalyptus, or IR3535 according to label instructions. Repellents keep the mosquitoes from biting you. DEET can be used safely on infants and children 2 months of age and older.

2. DAWN AND DUSK – Mosquitoes that carry WNV bite in the early morning and evening. It is important to use repellent and wear clothing that reduces the risk of skin exposure to mosquito bites during this time. Make sure your doors and windows have tight-fitting screens to keep out mosquitoes. Repair or replace screens with tears or holes.

3. DRAIN – Mosquitoes lay their eggs on standing water. Eliminate all sources of standing water on your property, including buckets, old car tires, and pet bowls. If you have a pond, use mosquito fish (available from your local mosquito and vector control agency) or commercially available products to eliminate mosquito larvae.

Residents can call their local Mosquito Abatement District to report a neglected swimming pools or ornamental ponds or with questions or concerns. In Stanislaus County, north of the Tuolumne River call East Side Mosquito Abatement District at 522-4098. All other residents may call Turlock Mosquito Abatement District at 634-1234.