FEATURE | Posted July 26, 2016

Increase in West Nile virus activity in California

Avoiding mosquito bites still best preventive

bird bath © iStockphoto
Since mosquitoes breed in stagnant water, it’s best to eliminate any areas around the home where water may collect, such as birdbaths or neglected swimming pools.

In California, warm summer nights and more outdoor activities often mean more mosquito bites. While mosquitoes leave an itchy reminder of their presence, there’s a more serious souvenir the bugs may leave behind: West Nile virus.

The majority of West Nile virus cases do not have symptoms, but 20 percent to 30 percent of people infected will have mild symptoms. Symptoms last for a few days and include fever, muscle aches, vomiting, joint pain and diarrhea. Only about one percent of cases are severe, known as neuroinvasive West Nile virus, and can cause seizures or meningitis.

Adults over 50 years of age and others with compromised immune systems, such as organ transplant recipients, are at a higher risk of a symptomatic West Nile virus infection.

West Nile virus activity high in Sacramento

The California Department of Public Health (CDPH) Director and State Health Officer Karen Smith reported increased West Nile virus activity across the state and reported the first human death from West Nile virus in August. The state is investigating other suspected cases in humans and has detected the virus in birds and mosquitos in 30 California counties. Sacramento County has the highest year-to-date number of dead birds and mosquito pools testing positive for the virus.

mosquito at dusk

In 2015, CDPH reported 860 human West Nile virus infections in California and 53 deaths.

Avoiding mosquito bites best West Nile virus prevention Because West Nile virus is transmitted by mosquito bites, Smith and Dean Blumberg, an associate professor of infectious diseases at UC Davis Children’s Hospital, advise everyone to practice the “Three Ds.”

1. DEET – Apply insect repellent containing DEET, picaradin, oil of lemon eucalyptus or IR3535 according to label instructions. Repellents keep mosquitoes from biting. DEET can be used safely on infants and children two months of age and older.

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

3. DRAIN – Mosquitoes lay their eggs on standing water. Eliminate or drain all sources of standing water around homes and properties, including buckets, old car tires, rain gutters, birdbaths and pet bowls. If a swimming pool is not being properly maintained, please contact the local mosquito and vector control agency.

For maximum protection from both harmful UV rays and mosquitos, Blumberg recommends using sunscreen first and then a mosquito repellant. And if West Nile virus symptoms arise after a mosquito bite, be sure to tell your health-care provider.

Help the experts monitor West Nile virus


Video: Learn how to help public-health and mosquito-control experts track West Nile virus by reporting when you find dead birds.

“West Nile virus is transmitted naturally between mosquitoes and birds, and some birds such as crows, jays, and magpies die from the infection,” said Chris Barker, assistant adjunct professor in the School of Veterinary Medicine at UC Davis. “Locating and testing these dead birds is a very important way of identifying areas where the virus is most active.”

If you see a dead bird, report it by phone at 877-WNV-BIRD or on the California Department of Public Health's West Nile virus website. If there’s a high number of West Nile virus infections detected in a particular area, local mosquito control agencies and the California Department of Public Health will increase their efforts to prevent its spread.

Related stories:

California West Nile virus website

Check up on health: Take steps to lower risk of diseases from mosquito bites