Adult mosquitoes emerge from pupae 1 to 2 days after that, with male mosquitoes always emerging first. In summer the entire life cycle, from egg to adult, may be completed in a week or less. The most important consequence of this is the transmission of microorganisms that cause diseases such as western equine encephalomyelitis and St. Louis encephalitis. Both of these diseases can cause serious, sometimes fatal neurological ailments in people. Western equine encephalomyelitis infections tend to be more serious in infants while St. Louis encephalitis can be a problem for older people.
Some mosquitoes are capable of transmitting malaria to humans.
Mosquitoes vector dog heartworm in California. Oak trees, common in foothill areas of California, provide tree holes that fill with water and harbor the larval stages of the principal vector of this disease. Even when no infectious diseases are transmitted by mosquitoes, they can be a health problem to people and livestock. Mosquito bites can result in secondary infections, allergic reactions, pain, irritation, redness, and itching. In California, there are more than 50 mosquito and vector control districts.