Health Advisory

“Although mosquitoes breed throughout the year in Southern California, the potential for disease transmission increases as the weather gets warmer,” said Frank Hall, Ph.D., chief of the county’s Vector Management Program.

Infected female mosquitoes can transmit St. Louis Encephalitis virus (SLE) to humans. Most SLE infections in humans are mild, producing only headache and fever. In severe cases – especially in the elderly – the virus infects the brain, causing confusion, paralysis, coma and even death. The only way for humans to acquire the disease is through the bite of an infected mosquito that has previously bitten a bird that carries the virus. SLE cannot be transmitted directly from person to person or from birds to people.

“Because mosquito breeding requires a water source, residents can reduce breeding by eliminating standing water around their yard,” said Hall. “Buckets, planters, old tires and other containers accumulate rain and landscape water and should be drained as soon as possible. These are perfect breeding sites for mosquitoes.”

Property owners should maintain ponds and pools with adequate filtration and chemical additives. Residents who know of a pool that is not receiving regular maintenance should report it to their local mosquito/vector control district office. These offices can also provide fish that thrive on mosquito larvae for use in residential ornamental ponds.

Property owners should install and maintain window and door screens to prevent mosquitoes from entering homes. Mosquitoes are most active at dusk and in the evening. Residents can protect themselves by avoiding mosquito-infested areas that may develop in heavily wooded areas near natural water sources like rivers, lakes and marshes. Residents visiting these areas during mosquito season should use insect repellent and wear protective clothing such as long pants and long-sleeved shirts with high collars.

Surveillance Activities for Mosquito-borne

Active surveillance for mosquito-borne encephalitis is conducted throughout the county from May through October by mosquito and vector control district offices. Flocks of chickens are placed in various areas of the county; blood from these chickens is tested routinely for evidence of infection with SLE, Western Equine Encephalitis (WEE) and West Nile virus (WNV). Evidence of infection with SLE virus has been found in chickens yearly from 1984 through 1998. Mosquitoes from various sites in the county are also tested for the presence of SLE, WEE and WNV. SLE virus has been found in mosquitoes sporadically since 1984.

Although there is no evidence that WNV has spread to the West Coast, the health department will test for the virus if warranted by a physician.

“Physicians treating patients for encephalitis are required to report the cases to the health department,” said Roshan Reporter, M.D., M.P.H., on the Acute Communicable Disease Control Unit. “The health department can also test for SLE and Western Equine Encephalitis at the physician’s request. The most recent death of a county resident from a confirmed case of SLE was in 1999; there were 25 cases between 1984 and 1992 including one death.

For help with mosquito problems, residents may call their local mosquito/vector control district: Greater LA County Vector Control District (800) 371-4402, (562) 944-9656, or (818) 764-2010 LA County West Vector Control District (310) 915-7370 Compton Creek Mosquito Abatement District (310) 639-7375 Antelope Valley Mosquito and Vector Control District (626) 814-9466 DHS’s Vector Management Program (626) 430-5450

For information regarding human diseases related to mosquitoes, call the Acute Communicable Disease Control Unit at (213) 240-7941.

Public Health is committed to protecting and improving the health of the nearly 10 million residents of Los Angeles County. Through a variety of programs, community partnerships and services, Public Health oversees environmental health, disease control and community and family health. Public Health comprises more than 3,800 employees and has an annual budget exceeding $465 million.