ABC’s of your Health: With Increasing West Nile Virus Activity in the state, Californians are urged to protect against mosquito bites

Reducing global warming can help lessen the extent of pests like mosquitoes.
Reducing global warming can help lessen the extent of pests like mosquitoes. Fresno Bee file

With increasing West Nile Virus Activity in the state, the state Department of Public Health (CDPH) is urging 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.

West Nile virus spreads to humans and animals through the bite of an infected mosquito.

As of June 28, the counties of San Joaquín, Merced, Fresno, Tulare and Kern had West Nile virus activity. However, no human cases have been reported in the state.

In mid-June, the Consolidated Mosquito Abatement District notified the Fresno County Department of Public Health of WNV positive tests in adult mosquitoes collected from an area around portions of the 93710 ZIP code area that is within the City of Fresno.

Leticia Berber, Health Educator Fresno County Department of Public Health said the positive test “is a strong reminder that everyone should take this disease seriously and should take every precaution to protect themselves and their families from mosquito bites.”

According to CDPH, the 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, according to CHPH and the risk of disease due to WNV increases as the summer progresses and declines in early fall as the weather cools.

According to CHPH, 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. Last year West Nile virus activity was detected in 41 counties in 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.

West Nile Virus can be deadly — but only one in five people who are infected by a mosquito bite will develop any symptoms, according to the South Carolina Department of Health and Environmental Control. Here's what to look for.

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


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.


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.


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.

Zika and West Nile viruses are both transmitted by mosquitoes. Officials from public health and from Sacramento-Yolo vector control explain how to protect yourself from bites.

Jeremy Wittie, president of the Mosquito and Vector Control Association of California (MVCAC). Said “protecting public health is a shared responsibility and we must all commit to making mosquito prevention part of our regular routine.”

According to the Mosquito and Vector Control Association of California, wasteful water practices are creating mosquito breeding grounds in backyards across the state from overwatering - or inefficient watering - of lawns and using excessive water to wash cars and driveways that can create standing water where mosquitoes lay eggs.

Unattended standing water in pet bowls and flowerpots can also create more urban mosquitoes which means greater risk of disease transmission in residential areas. In addition, abandoned swimming pools, ornamental ponds, septic tanks, and rain barrels, which are especially predominant in areas ravaged by wildfires, can contribute to mosquito breeding. Mosquitoes can breed in sources of water as small as a bottle cap, so it’s critical that residents inspect their yards weekly and remove any standing water.

“Responsible irrigation as well as dumping and draining all standing water in the yard are simple steps residents can take to eliminate mosquito habitats,” Wittie said.

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).

María G. Ortiz-Briones: 559-441-6782, @TuValleTuSalud