The Southern Nevada Health District declared an “outbreak of mosquito-borne diseases” Thursday.
Friday, a 6th case of the West Nile virus was reported in Clark County for the year.
Last year, Clark County had no reported human cases of West Nile.
The health district warns residents to take measures to prevent mosquito bites and to clear away standing water and other breeding conditions around homes.
Meanwhile, mosquitoes carrying West Nile have been spotted near the central Utah city of Aurora.
The Central Utah Public Health Department says officials detected the virus earlier this week. They received test results confirming the virus on Friday.
Aurora is the second city in Utah to report infested mosquitoes this year. The virus was detected in Moab earlier this month.
According to the Utah Health Department no residents have contracted West Nile virus this year.
In 2018 11 residents contracted the virus and one person died. Symptoms can include headaches, joint pains and a high fever.
State health officials said the wet spring Utah experienced this year has created more standing water habitats for mosquitoes. This increases the likelihood of species that can transmit West Nile virus coming to Utah.