Humidity Boosts Mosquito Survival, Driving Surge in West Nile Cases in Los Angeles County

Los Angeles County health officials reported 100 West Nile virus infections this year, including five deaths, the highest number of cases in more than ten years. Experts attribute the rise to an unusually humid summer driven by El Niño conditions, which have prolonged mosquito survival and increased biting activity.

Dr. Photini Sinnis of the Johns Hopkins Bloomberg School of Public Health explained that humidity prevents mosquitoes from desiccating, allowing infected insects to live longer and transmit the virus to more people. She noted that mosquitoes can survive for several weeks and feed on blood roughly every four days.

The county’s Department of Public Health said 73 of the cases were men, 27 women, with a median age of 64.5 years. About 90 patients developed neuroinvasive disease, a serious condition that can cause inflammation of the brain and surrounding tissues. Roughly one-third of the infections occurred in East Los Angeles, with additional cases in the San Fernando Valley and South Bay.

Health Officer Dr. Muntu Davis warned that the region remains in the peak transmission period, which typically runs from June to October, and urged residents to take protective measures. The Centers for Disease Control and Prevention noted that there is no specific treatment for West Nile virus, and severe cases may require hospitalization for supportive care.

Long Beach, the first city in the county to report a human case, has recorded 42 infections this year, including 26 neuroinvasive cases, but no deaths. City health officer Dr. Cliff Okada said the local vector-control district has stepped up surveillance, public education, and mosquito-control treatments in affected neighborhoods.

Both officials highlighted that warm, humid weather historically increases mosquito activity, and that broader climate trends are contributing to a rise in mosquito-borne diseases nationwide.