Health officials say a person who contracted West Nile virus in Shelby County is Tennessee’s third case of the illness this year. In a news release Friday, the Shelby County Health Department did not identify the person who got the illness, which is transmitted to humans through mosquito bites. The West Nile virus can occasionally cause severe disease or even death. But most human infections are mild and cause fever, headache and body aches that last a few days. Crews have been treating mosquito breeding sites with insecticides and setting traps to capture and kill the insects.