Summer is here and with that comes mosquito season. Did you know that mosquitoes are responsible for more human deaths than any other animal in the world? There is a long list of diseases spread by the bites of mosquitoes. In Orange County, the most common disease spread by mosquito bites is West Nile virus (WNV).
Most people infected with West Nile virus never develop symptoms. Some may experience a short‑lived fever that goes away on its own. In rare cases, the virus can infect the brain and cause encephalitis, which can lead to severe illness or death. People who develop encephalitis may have complications such as paralysis, coma, or long‑term cognitive impairment. Fewer than one in a hundred infected individuals develop encephalitis, but the risk is highest among older adults, those with multiple underlying health conditions, and people with weakened immune systems.
West Nile virus was known to circulate in parts of Africa for many years. In 1999, it was detected for the first time in people in the New York area who had no travel history, and mosquitoes in the same area tested positive for the virus. Despite mosquito‑control efforts, West Nile virus spread across the country. In Orange County, the first human cases were identified in 2004, and the highest number occurred in 2014, when 280 infections were reported.
This summer, 2026, many mosquito samples in Orange County have already tested positive for West Nile virus. There is concern that the large number of mosquitoes testing positive so far could lead to higher numbers of people becoming infected this summer and fall.
Because there is no specific treatment for West Nile virus, it is very important to protect yourself from mosquito bites. Removing mosquito breeding areas around your home, such as stagnant water, making sure screens are intact, wearing long sleeves when outside around dusk and dawn when the mosquitoes who carry West Nile virus are most active, and using EPA-registered, mosquito repellent outside during dawn and dusk will help prevent bites. The Orange County Mosquito and Vector Control Agency has valuable resources on protecting your household from mosquitoes as a part of their Mosquitoes Suck! Campaign. The California Department of Public Health also has a wealth of information on their mosquito repellents website.
Resources
- OC Vector Control
- Mosquitoes Suck Campaign
- Make Your Home Mosquito Free
- Report an Issue
- West Nile Virus Activity in Orange County
- California Department of Public Health – Mosquitoes
- Environmental Protection Agency – Find the Right Repellant for You
- Environmental Protection Agency – Using Repellants Safely
About Dr. Christopher Zimmerman
Dr. Christopher Zimmerman is board certified in both Internal Medicine and Pediatrics. He has more than a decade of experience as a primary care physician taking care of both adults and children. Dr. Zimmerman also trained as an Epidemic Intelligence Service Officer with the Centers for Disease Control (CDC), and holds a Master's in Public Health from the Harvard School of Public Health. He has extensive experience on vaccination and vaccine preventable diseases from the CDC, the New York City Department of Public Health, as well as working on the Global Polio Eradication Initiative with the World Health Organization.