West Nile Virus
Mosquito-Borne Disease

"Some species of mosquitoes are involved in the transmission of important human and veterinary disease-causing agents (pathogens). In California these diseases include encephalitis (several viruses), malaria (a protozoan) and dog heartworm (a roundworm). The biological transmission of these and other mosquito-borne pathogens is a complex and highly evolved interaction among the vertebrate host, the pathogen and the mosquito (vector). Most pathogens of humans, such as measles, hepatitis or HIV (AIDS) viruses cannot develop in mosquitoes, whereas many pathogens of mosquitoes such as iridescent virus cannot develop in vertebrates.

Additional information from California Department of Public Health on mosquito disease.