Increasing West Nile Virus Activity in California

Californians Urged to Protect Against Mosquito Bites

SACRAMENTO June 26, 2019 – The California Department of Public Health (CDPH) urges all Californians to protect themselves from mosquito bites during West Nile virus (WNV) season, which extends from now through early fall.

“West Nile virus activity in the state is increasing, so it is important to take every possible precaution to protect against mosquito bites,” said State Public Health Officer and CDPH Director Dr. Karen Smith.

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West Nile virus spreads to humans and animals through the bite of an infected mosquito. Late-spring rains have contributed to standing water, which serves as a breeding source for mosquitoes that can spread WNV. Hot temperatures also contribute to increasing numbers of breeding mosquitoes and an increased risk of virus transmission to humans. Currently, WNV activity is within expected levels and is similar to activity at this time last year. The risk of disease due to WNV increases as the summer progresses, and declines in early fall as the weather cools. In 2018, there were 217 reported WNV cases in California, including 11 deaths. Since WNV was first introduced into California in 2003, there have been more than 6,000 human WNV cases and 303 WNV-related deaths across the state.

West Nile virus is influenced by many factors, including climate, the number and types of birds and mosquitoes in an area, and the level of WNV immunity in birds. For most people, the risk of developing serious illness is low. However, some individuals – less than one percent – can develop serious neurologic illnesses such as encephalitis or meningitis. People 50 years of age and older, and individuals with diabetes or hypertension, have a higher chance of getting sick and are more likely to develop complications from WNV infection.

 CDPH recommends that people protect against mosquito bites and WNV by practicing the “Three Ds”:

1. DEET – Apply U.S. Environmental Protection Agency (EPA)-registered insect repellent containing DEET, picaridin, oil of lemon eucalyptus, or IR3535 according to label instructions. EPA-registered repellents are recommended for use because they have been tested for safety and efficacy in preventing mosquito bites. Insect repellents should not be used on children under two months of age. For more information, visit CDPH’s insect repellent toolkit.

2. DAWN AND DUSK – Mosquitoes that transmit WNV usually bite in the early morning and evening, so it is important to wear proper clothing and repellent if outside during these times. Make sure that your doors and windows have tight-fitting screens to keep out mosquitoes. Repair or replace screens that have tears or holes.

3. DRAIN – Mosquitoes lay their eggs on standing water. Eliminate all sources of standing water on your property by emptying flower pots, old car tires, buckets, and other containers. If you know of a swimming pool that is not being properly maintained, please contact your local mosquito and vector control agency.

California’s West Nile virus website includes the latest information on WNV activity in the state. Californians are encouraged to report dead birds on the website or by calling toll-free 1-877-WNV-BIRD (968-2473).