There has been a lot of public concern and confusion about mosquitoes and AIDS. Scientific studies conducted by the Centers for Disease Control and the World Health Organization have shown that mosquitoes DO NOT transmit AIDS. For more information, here is an article from Nature.com about why mosquitoes cannot transmit AIDS.
In California, mosquitoes are monitored and controlled primarily for public health reasons, such as West Nile Virus, malaria, encephalitis, dog heartworm and sensitivity to bites. Some mosquitoes are also controlled because of their annoying habits.
With the exception of recent West Nile Virus cases, human mosquito-borne diseases have declined significantly in California since the creation of mosquito and vector control agencies. Residents should be aware that West Nile Virus, dog heartworm and encephalitis viruses are still present in Napa County.