LAS VEGAS – The Southern Nevada Health District has identified two cases of West Nile virus for this season. One patient, a male over the age of 60, was diagnosed with the non-neuroinvasive form of the illness, and a male over the age of 70, had the neuroinvasive form of the illness. Both patients have recovered.
The announcement of the first reported cases in Clark County residents occurs after the Health District reported the highest level of mosquito activity in the program’s history this early in a season. As of June 21, 2024, 230 mosquito pools (7,493 mosquitoes from 30 ZIP codes) tested positive for West Nile virus. Nine mosquito pools, (267 mosquitoes from five ZIP codes) tested positive for the virus that causes St. Louis encephalitis.
Public health officials are encouraging everyone to take steps to protect themselves. The risk of mosquito-borne illnesses can be reduced through preventive measures. The Health District’s Fight the Bite campaign calls on people to:
- Eliminate Standing Water: Remove 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: Use Environmental Protection Agency (EPA)-registered insect repellent. Wear loose-fitting, long-sleeved shirts and pants.
- Report Mosquito Activity: Call the Health District’s surveillance program at (702) 759-1633. To report a green pool, people should contact their local code enforcement agency.
The Health District’s Mosquito Surveillance Program continues to receive 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. Aedes aegypti lay eggs on the inner walls of small containers that hold water and their eggs can remain dry and dormant until the next time water fills the container and they hatch. While the species is known for transmitting viruses such as dengue and chikungunya, Aedes aegypti mosquitoes tested in Clark County have tested positive for West Nile virus this season.
The majority of the mosquitoes trapped and testing positive for West Nile Virus and St. Louis encephalitis are Culexspecies, which prefer to feed on birds and are responsible for maintaining the virus in avian populations. Although Culexprefer to feed on birds, they will bite people and can transmit the virus when they do. Culex lay eggs on the surface of fresh or stagnant water, including unmaintained swimming pools, horse troughs, ornamental ponds and marshy areas.
Mosquitoes testing positive for St. Louis encephalitis virus were last reported in Clark County in 2019 and the last reported cases in humans were in 2016. West Nile virus activity was minimal in 2020 through 2023. In 2019, 43 human confirmed cases were reported. There was one case reported in 2022 and two confirmed cases were reported in 2023.
Both St. Louis Encephalitis and West Nile virus are spread to people by the bite of an infected mosquito. Most people infected with the virus will not develop symptoms and their cases will go unreported. Some people may develop a neuroinvasive form of the illnesses that cause encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes surrounding the brain and spinal cord).
For more information, Health District Fight the Bite tips and resources are available at www.southernnevadahealthdistrict.org/programs/mosquito-surveillance/mosquito-bite-prevention/ or on the Centers for Disease Control and Prevention website at www.cdc.gov/mosquitoes/prevention/index.html.
The Health District’s seasonal mosquito surveillance reports are available at www.southernnevadahealthdistrict.org/programs/mosquito-surveillance/arbovirus-update/.