The department said the child was experiencing neurological symptoms and was hospitalized.
Between 2013 and 2015, there were no reported human cases with only single cases reported in 2016 and 2017.
The Department of Public Health and Wellness said in a release that surveillance traps in three local zip codes turned up infected mosquitoes including 40212, 40213, and 40214.
Mosquitoes with West Nile virus have been found in Louisville.
The first case of West Nile virus infection in Virginia this year has been reported in Fairfax County, coming on the heels of a confirmed case in Maryland.
Manitoba child the province's first human case of West Nile for 2018
"In recent years, when one human case occurs in an area, other cases often follow in the same part of the county", Fairfax officials said.
The health department operates a mosquito control program and checks traps set in the community to test for diseases like West Nile, Zika and St. Louis Encephalitis. The majority of people who develop this type of West Nile virus recover completely, but fatigue and weakness can last for weeks or months.
People infected with West Nile virus may show no or very mild symptoms.
Those most at risk for serious complications are people older than 50 and people with suppressed immune systems. Symptoms can include muscle aches, headache and fever. Anyone who thinks they may be infected should see a doctor immediately, officials said.
Homeowners are also asked to eliminate standing water by cleaning eaves troughs, emptying bird baths, covering rain barrels with mosquito screens, getting rid of containers that collect water and landscaping for better drainage.
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