Warm weather and pools of water create a perfect breeding ground for mosquitoes, so as temperatures begin to climb, the San Benito County Agricultural Commissioner’s mosquito abatement district staff members are preparing for their busy season.
Ron Terry, an agricultural biologist/inspector III, and a seasonal employee do most of the work to keep the mosquito populations down while also monitoring the bugs for West Nile Virus.
Though West Nile Virus has not been found in San Benito County since 2006, it has been found in many of the counties that surround it, such as Fresno, Merced, Santa Clara and Santa Cruz, according to the California Department of Health.
“Everything around us has found them,” Terry said. “The real question is, ‘Why not here?’”
He had a few answers, noting that San Benito County is a smaller area that is more compressed and a bit isolated. He said the temperatures in San Benito County, which has a milder springtime and cooler evenings, helps to keep the populations down. But mostly, he said, the mosquito abatement staff members have been vigilante about keeping populations curtailed.
“We have been very aggressive in trying to deal with it,” he said. “The main issue is abandoned swimming pools.”
A variety of mosquito species are found in San Benito County, but the staff members are most concerned with those varieties that carry West Nile Virus. San Benito County voters approved an assessment district to cover the cost of mosquito abatement in 2007 after the state passed a mandate that all counties had to provide some services in response to the spread of WNV. There are 10 traps in the county to monitor what type of mosquitoes are around and the staff members maintain a flock of chickens that is tested for the virus regularly. The chickens don’t show any symptoms if infected, but can be a sign that a problem is arising.
The state health department is still testing dead birds and residents can report any dead birds they see to 1-877-WNV-BIRD (1-877-968-2473.) Terry said one of the key ways residents can help is to report the birds so public health officials can pick them up and send them in for testing.
West Nile impact:
In 2004, there were 29 fatal human cases of West Nile Virus in the state, according to the state health department, with a total of 110 deaths since 2003.
West Nile Virus has varying impacts on humans, from no symptoms in about 80 percent of those infected with the majority of others having symptoms similar to a bad case of the flu. But in 1 in 150 people infected, the disease causes high fever, headache, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness and paralysis that last several weeks and neurological effects may be permanent. The virus can also be fatal.
The number of infected humans, horses and birds has declined since 2003, with nine fatal human cases in 2011.
The main culprit for growing mosquito populations in San Benito is abandoned pools. When a pool is left without being treated with chlorine, a new batch of mosquito larvae can hatch every 10 to 15 days and the adult bugs spread out through the neighborhood. The mosquito season starts when temperatures warm, but is at its peak from August to mid-October in San Benito County, Terry said.
The abatement staff members are keeping an eye on about 70 pools, many attached to foreclosed homes. In the past, Terry has relied on tips from residents to locate problem areas. But this year, the office hired a company to fly over and take aerial photos of the city during the first week of June.
“It’s been very helpful,” Terry said, “It makes the job so much more efficient.”
Looking at the photos, Terry said, he can pinpoint pools or other water features that may be of concern. With an image pulled up on his computer screen, Terry showed how a healthy pool has a clear, but slightly green tinge versus a green pool that appears dark in the aerial photo. Another above ground pool was bright blue and Terry guessed it probably had a pool cover on it.
He said most homeowners have been helpful, allowing him into the yard to check out the pools. If there is a mosquito issue, he approaches it in two ways. If the home is up for sale and likely to be sold soon, he will treat it with an oil that kills the larvae. If the home is abandoned or the owners no longer want to maintain the pool, he will use mosquito fish. The fish eat the larvae and will keep the water clean indefinitely until someone puts chlorine in it.
“What it has allowed us to do is be very specific on what we check on, and we can do it very quickly,” Terry said.
For next year, Terry would like to hire the company again, but said he will try to schedule it for the end of June. He said when he visited some of the homes with green pools in the aerial shots, by July the families had cleaned up the pools. He speculated that some families might wait until school lets out or the weather warms up to get the pools back into shape.
Mosquitoes can breed in other collections of water as well so his staff puts a natural insecticide in the storm drains in June, which lasts six months. The insecticide is non-toxic and not harmful if it gets into the waterways, he said. They will also spray in rural areas where there might be a growing population of mosquitoes. Residents can call in to report issues with mosquitoes and the staff members will check for problems, such as flower pots, birdbaths or even old tires collecting water where larvae can flourish.
The last reported cases in San Benito included dead birds and infected horses in 2004 to 2006. Though there has not been a reported case if West Nile Virus in San Benito since 2007, Terry said it is important to continue the abatement work.
“If we weren’t taking care of the swimming pools, I’d hate to think what the town would be like,” Terry said.
