More Aedes aegypti mosquitoes have been discovered in the region.
The district has already been making efforts to trap and eradicate them from neighborhoods in East San José and Gilroy.
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Staff are going door to door to check properties, and treating as needed at no cost to residents.
These mosquitoes are an invasive species - and can spread diseases like yellow fever and other deadly diseases like Zika, chikungunya, and dengue.
Experts say these mosquitoes prefer humans and are aggressive compared to others. They will also bite at day as opposed to other mosquitoes.