Officials with the Jefferson County, Ky. Health Department said that at least one mosquito infected with West Nile Virus has been found at Churchill Downs.The discovery of the mosquito came during a routine examination of a group of insects collected at the Louisville track. Local health officials have made regular checks of mosquitoes at the track since the November death of a 2-year-old Thoroughbred at Churchill Downs that was later found to be infected with West Nile Virus. That is the only reported death of West Nile-infected horse at a Kentucky racetrack. No other cases of human or equine infection have been reported at the track."Churchill Downs has been working with local and state health officials to ensure that we are taking every possible precaution to protect the humans and horses at our track," said John Long, acting president of Churchill Downs.Along with regular checks by health officials, the track has worked to control the mosquito population through constant monitoring of its drainage system and in other areas where water could become stagnant and promote the breeding of the insects.