Two mosquito pools also test positive for St. Louis Encephalitis

 Southern Nevada Health District officials are reminding people to protect themselves from mosquitoes as they report the highest level of activity in the program’s history this early in a season. As of June 6, 2024, 91 mosquito pools, comprising 3,081 mosquitoes from 16 ZIP codes, have tested positive for West Nile virus. Two mosquito pools, comprising 46 mosquitoes from two ZIP codes, have tested positive for the virus that causes St. Louis encephalitis.

The Health District’s Mosquito Surveillance Program has also received an increased number of complaints from the public about mosquito activity. Increased awareness and reporting of mosquito activity are attributed to the expansion of Aedes aegypti mosquitoes throughout the region. Aedes aegypti mosquitoes are known to be aggressive daytime biters that prefer feeding on people instead of birds and are not typical vectors for West Nile virus. A single Aedes aegypti tested positive in 2017, and a submission pool of 22 mosquitoes tested positive in 2023.

Mosquitoes testing positive for St. Louis encephalitis virus were last reported in Clark County in 2019 and the last reported cases in humans in 2016. St. Louis encephalitis virus is spread to people by the bite of an infected mosquito. Most people infected with the virus will not develop symptoms. People who become ill may develop fever, headache, nausea, vomiting and fatigue. Some people may develop a neuroinvasive form of the disease that causes encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes surrounding the brain and spinal cord).

There was minimal West Nile virus activity reported in 2020, 2021, and 2023. In 2019, 43 confirmed human cases were reported. Two human cases of West Nile Virus were reported in 2023. West Nile virus is spread to people through the bite of an infected mosquito. About one in five people infected with West Nile virus will develop symptoms that can include fever, headache, body aches, vomiting, diarrhea or rash. About one in 150 will develop more serious, sometimes fatal, illness. People who think they might have West Nile should talk with their health care provider.

The risk of mosquito-borne illnesses can be reduced through preventive measures. The Health District’s Fite the Bite campaign calls on people to:

  • Eliminate standing water and other breeding sources around their homes. Aedes aegypti breed in small containers that collect rain or irrigation water, such as children’s toys, wheelbarrows and plant saucers, and even bottle caps.
  • Prevent mosquito bites by using an Environmental Protection Agency (EPA)-registered insect repellent. Wear loose-fitting, long-sleeved shirts and pants.
  • Report mosquito activity to the Health District’s surveillance program at (702) 759-1633. To report a green pool, people should contact their local code enforcement agency.

More Fight the Bite tips and resources are available at and on the Centers for Disease Control and Prevention website at

The Health District’s seasonal mosquito surveillance reports are available at

The Southern Nevada Health District serves as the local public health authority for Clark County, Boulder City, Henderson, Las Vegas, Mesquite and North Las Vegas. The agency safeguards the public health of the community’s residents and visitors through innovative programs, regulations, and initiatives focused on protecting and promoting their health and well-being. More information about the Health District, its programs, services, and the regulatory oversight it provides is available at Follow the Health District on Facebook, Twitter, and Instagram.