West Nile Virus has returned to peninsula: http://www.almanacnews.com/news/2016/07/28/west-nile-virus-found-in-atherton
The specific of mosquito (Aedes Aegypti) that carries the West Nile virus can also pass along other diseases, including Dengue Fever, Yellow Fever, and the Zika virus.
CERT members have participated with the +San Mateo County Mosquito Abatement Program to increase awareness of this particular mosquito and how to reduce its breeding places and protect yourself from its bite.
For more information about the various diseases that can be transmitted by this and other mosquitoes, go to:
West Nile - http://www.cdc.gov/westnile/index.html