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Yellow fever mosquito found in county
St. Louis encephalitis virus is a mosquito-borne virus, similar to West Nile Virus. - photo by Photo courtesy of the Centers for Disease Control

If West Nile and the Zika viruses weren’t enough to keep people taking precautions against mosquito bites then a new threat looming in a neighboring county might just do the trick.

“We’re very concerned about the eventual appearance of the yellow fever mosquito (Aedes aegypti) in Stanislaus County,” said Turlock Mosquito Abatement District General Manager David Heft. “Merced County has made numerous detections of this mosquito and it is just a matter of time before we see this mosquito in Stanislaus County. TMAD has significantly increased our surveillance for this mosquito as well as targeted our public outreach message for the public to be aware of daytime biting mosquitoes around the home. Quick detection of this mosquito may give us a chance to eradicate the mosquito from the area before it becomes established, like it has in Merced County.”

The Aedes aegypti mosquitoes are active during the day and are carriers of several diseases, including dengue fever, chikungunya, Zika virus, and yellow fever. They live in close proximity to humans, with some spending their entire life cycle indoors.

“This makes controlling these mosquitoes very difficult,” Heft said. “Our “typical” dusk/dawn treatments will not be effective since these mosquitoes aren’t active at those times. The close proximity to humans means a literal door-to-door, backyard-to-backyard process which is very costly and labor intensive.”

So far, Stanislaus County has not had any local acquisition of these diseases, though some individuals have contacted them while out of the area. If these mosquitoes are able to get established in the area then the chances of local transmission would increase dramatically.

The possibility of a new threat does not lessen the impact of the current one from West Nile Virus. Stanislaus County recorded the first human case this season last week, while the state tally has grown to 19 from 11 counties.

San Joaquin, Sacramento and Placer counties have seen the bulk of West Nile Virus activity with dead birds and mosquito pools in the state, but it’s expected Stanislaus County will soon see an increase.

“We expect more activity in Stanislaus County as the summer wears on and harvesting activities displace habitat causing mosquitoes to move into suburban areas,” Heft said.

Mosquitoes become infected with West Nile Virus 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. 

There are no medications to treat or vaccines to prevent West Nile Virus infection. People with milder illnesses typically recover on their own, although symptoms may last for several weeks or months. In the neuroinvasive forms, patients can suffer severe and sometimes long-term symptoms.

“As temperatures increase, mosquitoes and the diseases they transmit have encroached into new areas,” Heft said. “West Nile Virus has only been in Stanislaus County for less than 15 years. These significant challenges rarely come with additional funding, so the District has become more aggressive in pursuing property owners that routinely breed mosquitoes. This includes owners who routinely have neglected swimming pools. The District does aerial fly-overs at least twice a summer to spot neglected pools so that we can treat them to prevent thousands of mosquitoes from being released into neighborhoods. Owners who are found that frequently neglect the maintenance of their swimming pool run the risk of an abatement being filed subjecting them to reimburse our cost for controlling the nuisance and civil penalties.”

Health officials urge people to follow the three Ds when it comes to preventing mosquito bites:

1. DEET – Apply insect repellent containing DEET, picaradin, oil of lemon eucalyptus or IR3535 according to label instructions. 

2. DAWN AND DUSK – Mosquitoes that transmit WNV usually bite in the early morning and evening so it is important to wear proper clothing and repellent if outside during these times. 

3. DRAIN – Mosquitoes lay their eggs on standing water. Eliminate all sources of standing water on your property by emptying flower pots, old car tires, buckets, and other containers. 

If you know of a swimming pool that is not being properly maintained, please contact your local mosquito and vector control agency.

Reporting and testing of dead birds is an important step in preventing West Nile Virus. A confirmed case of the virus in dead birds or mosquito samples helps to identify areas that need treatment to reduce mosquito activity. To report a dead bird, call the California State hotline at 1-877-WNV-BIRD or report it online at Birds of particular interest are crows, ravens, magpies, jays and raptors (hawk or eagle).

The Turlock Mosquito Abatement District is available to help with neglected pools in the prevention of mosquito development. To request District

service, call 634- or visit the District website at