Mosquito-borne illnesses such as malaria or Zika are typically associated with travel outside the United States. But West Nile virus is routinely found in California during the warmer months. In May 2026, the first mosquito sample of the season in Sacramento County tested positive for West Nile virus.
West Nile virus was first found in the U.S. in 1999 and arrived in California in 2003. It can cause flu-like symptoms and is the most common mosquito disease in the U.S. In 2025, there were 124 confirmed human cases of the virus in California, including 11 deaths.
There are three things you can do to protect against mosquitoes and mosquito-borne illnesses, such as West Nile virus: Cover, control and repel.
1. Cover up
While it may be hot outside, wear loose-fitting, long sleeves and pants when you can. This helps keep mosquitos off your skin. Parents can also cover strollers and baby carriers with mosquito netting.
You can also use 0.5% permethrin to treat clothing and gear (such as boots and tents).
Permethrin is a highly effective insecticide that works against dozens of pests, including mosquitoes, ticks, fleas, mites, chiggers and lice. It both repels and kills insects and can continue providing protection even after multiple washes. You should never use permethrin directly on the skin. It’s available at hardware, outdoor and sporting goods stores, as well as online.
Learn more about vector-borne diseases, like West Nile virus
2. Control mosquitoes around your home
Mosquitos love standing water, such as dog bowls and saucers from plants. Mosquitos can even breed in something as small as a bottle cap with water.
Be sure to get rid of any standing water around your house. The Centers for Disease Control and Prevention (CDC) recommends that you empty, scrub or turn over items that hold water at least once a week.
It's also a good idea to use screens on windows and doors to keep mosquitoes out of your house. Make sure to repair any holes in the screens.
Sign up for our Health Highlights e-newsletter
3. Repel mosquitoes
Use insect repellent on yourself and your family when you're outdoors. DEET is one of the most common and highly recommended types of insect repellent.
Insect repellent is safe to use, according to UC Davis Health pediatricians. You can see a list of repellents recommended by the Environmental Protection Agency and the CDC.
To protect children, avoid spraying products like DEET to the face or hands. Instead, apply a small amount to your own hands first, then lightly spread it on exposed skin. Be careful around the eyes, mouth and other sensitive areas. Always follow the instructions on the label.
If you are using sunscreen with repellent, apply the sunscreen first. Then use insect repellent over it.
Learn more tips for mosquito prevention from the CDC
What should you do if you get bitten by a mosquito?
If you get bitten, avoid scratching the bite area. Wash the area and apply an ice cube or ice pack for 30 seconds. Applying pressure to the bite may also soothe the itchiness. You can use a non-prescription antihistamine cream or calamine lotion.
About 8 out of 10 people infected with West Nile virus don't develop symptoms. The CDC has a list of symptoms for West Nile virus. If you believe you might have West Nile virus, contact your health care provider. There are no vaccines or medications to treat or prevent West Nile virus. Antibiotics do not treat the virus.
Symptoms of malaria are much like the flu. If you think you've been exposed to malaria, tell your health care provider so you can get tested. There are no vaccines for malaria.
If you think you may have been exposed to a mosquito-borne illness during travel – or if you're planning a trip and want to learn about recommended vaccines or preventive medications – talk with your health care provider. The Traveler's Clinic at UC Davis Health offers consultations before and after travel to help you stay safe.
See how the Traveler's Clinic can help you prepare for your next trip
This blog was medically reviewed by infectious disease specialist Natascha Tuznik.
