FRESNO, Calif. (KFSN) -- The West Nile virus has not made any humans sick in Fresno County this year, but the potential for infections is growing.
West Nile virus arrived in Fresno County in 2004 and the Consolidated Mosquito Abatement District has stayed busy ever since.
"Every year it's here, so even though we do surveillance, we're always collecting West Nile virus mosquitoes in this area," said Katherine Ramirez with the Consolidated Mosquito Abatement District.
Employees go to ponding basins and neglected swimming pools and use fish or larvicide to control the mosquito population.
But some infected insects always slip through the preventive shield.
This year, they've collected 46 Culex mosquitoes with serious viruses.
43 had West Nile virus; three had St. Louis encephalitis.
"We do an ultra-low volume spray in an area when we do find infected mosquitoes. We also continue to do surveillance to make sure that mosquito population has been reduced," said Ramirez.
It's kept people in Fresno County safe so far this year.
But their collection of infected Culex mosquitoes has now spread across Fresno, Clovis, and Sanger putting people in danger of getting an infection causing problems ranging from flu-like symptoms to paralysis and tremors.
And the Aedes aegypti mosquito can be even worse.
They can carry chikungunya, yellow fever, dengue fever, and Zika and they're a lot hungrier than Culex mosquitoes, which might eat blood once every two weeks.
"It's an extreme nuisance mosquito. It will bite repeatedly. So a lot of times someone thinks they have a huge mosquito problem because of the perception of the number of bites," said Ramirez.
The mosquito abatement district teamed up with an arm of Google for an experiment to reduce Aedes aegypti, pouring sterile male mosquitoes into neighborhoods and it's showing positive results.
They say they've detected 95% fewer females in those areas, and the females are the only biting mosquitoes.
The biters are still out there, though, so insect repellent is a necessity, especially at dusk and dawn.
46 mosquitoes with serious viruses found in Fresno County
WEST NILE VIRUS