Fifteen years ago, Aedes aegypti mosquitoes, the Zika vector, arrived in El Monte in bamboo imported from Southeast Asia. The mosquitoes are now found in 12 counties in California, with a particularly high population in the San Gabriel Valley. Although local Zika transmission has not been reported in California, 479 residents have contracted the virus in other countries and returned to the state and three babies born to infected mothers have birth defects. In addition, there is frequent travel from California to countries with outbreaks. Because a vaccine will not be available for years, public health officials are focusing on vector control.
Because spraying insecticides does not work as well on Aedes mosquitoes compared to Culex mosquitoes, vector control agencies have focused on sending workers door-to-door to check for standing water. The task is tedious since mosquitoes require only a few drops of water to breed. In El Monte and the Central Valley, male mosquitoes infected with bacteria have been released since their infection renders them sterile. However, this project would likely require federal approval to become widespread. In addition, the Los Angeles County Department of Public Health is setting up surveillance programs at clinics in areas where local transmission is more likely to occur. These programs involve testing people with symptoms of Zika. However, Zika infection is usually asymptomatic, so the virus could be transmitted locally among many people before anyone realized that local transmission was occurring.