The state Department of Public Health said Wednesday that 31 infected people died in 2014, the most since California began recording West Nile cases in 2003. Officials also said there were 801 Californians who tested positive for the virus — coming close to the record of 880 cases a decade ago.
Department head Dr. Karen Smith said the state’s prolonged drought likely had a role in the increased virus activity by creating more limited sources of water for birds and mosquitoes. Smith said the dry spell could have caused some sources of water to stagnate.
“As birds and mosquitoes sought water, they came into closer contact and amplified the virus, particularly in urban areas,” Smith said. “The lack of water could have caused some sources of water to stagnate, making the water sources more attractive for mosquitoes to lay eggs.”
California is in its fourth-consecutive dry year after a dismal wet season that saw below-normal rainfall and diminishing snowpack in the Sierra Nevada Mountains.
So far, there have been no reported human cases of West Nile virus in California in 2015. Cases involving birds have been reported in Los Angeles, Alameda, Santa Clara and San Diego counties.
Officials can’t predict West Nile virus activity in 2015, but said it will be influenced by climate, the number and types of birds and mosquitoes in a given area and the birds’ level of immunity.
Scientists have been sounding the alarm over the link between climate change and infectious disease, warning that the incidence and geographical reach of vector-borne diseases are rapidly increasing due to the effects of global climate warming.
West Nile is usually transmitted to humans from a bite by an infected mosquito. Symptoms can include high fever, a severe headache and confusion or a stiff neck; people 50 and above and individuals with diabetes and/or high blood pressure are at greatest risk to develop complications.
Of the 801 total cases in California, 561 patients developed a serious neurological form of the disease, which can often result in swelling of the brain.
State health officials recommend that individuals prevent exposure to mosquito bites and West Nile virus by practicing the “Three Ds:”
1. DEET: Apply insect repellent containing DEET, picaridin, oil of lemon eucalyptus or IR3535 according to label instructions. Repellents keep the mosquitoes from biting you. DEET can be used safely on infants and children 2 months of age and older.
2. Dawn and Dusk: Mosquitoes bite in the early morning and evening so it is important to wear protective clothing and repellent if outside during these times. Make sure that your doors and windows have tightfitting screens to keep out mosquitoes. Repair or replace screens with tears or holes.
3. Drain: Mosquitoes lay their eggs on standing water. Eliminate all sources of standing water on your property, including flower pots, old car tires, and buckets. 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 West Nile virus activity in the state. Californians are encouraged to report all dead birds on the website or by calling toll-free 1-877-WNV-BIRD (968-2473).