The Shelby County Health Department said Tuesday that the virus was found in two south Memphis zip codes. Mosquitoes can transmit West Nile virus to humans through bites.
Crews are treating mosquito breeding sites with insecticides and setting traps to capture and kill the insects.
Standing water found in rain gutters, downspouts, buckets, tires and other receptacles can serve as breeding grounds for mosquitoes.
The West Nile virus can occasionally cause severe disease, but most human infections are mild and cause fever, headache and body aches that last a few days.
There have been no human cases in Shelby County in this year. Three people died of West Nile virus in 2018.
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