In North America, cases of West Nile virus (WNV) occur during mosquito season, which starts in the summer and continues through fall.
"The objective of aerial spraying is to control mosquito populations; however, it does not eliminate all mosquitoes", Oswego County Public Health Director Jiancheng Huang said in a news release. WNV cases have been reported in all of the continental United States.
The city of Frisco has confirmed 18 mosquito pools that have tested positive for West Nile virus so far this year. About one in five people who become infected develop a fever with other symptoms such as headache, body aches, joint pains, vomiting, diarrhea, or rash.
Elderly people and individuals with suppressed immune systems are at risk for more serious illness.
The Oswego County Health Department said Wednesday that a horse in the town of West Monroe contracted Eastern equine encephalitis, a mosquito-borne virus.
In San Luis Obispo County, a dead bird found in Atascadero on September 18 tested positive for West Nile virus. "Mosquito season in OH lasts until the first freeze which is not usually until mid-October".
Avoid outdoor activity when mosquitoes are most active, especially at dusk and dawn.
Residents are advised to empty standing water on their property and wear long sleeves and repellents when outdoors.