Hidalgo County announced on Monday that three people had tested positive for the West Nile virus.

Two of the cases originated in Mercedes, according to a news release from Hidalgo County. One case originated in Weslaco.

"West Nile virus (WNV) is the leading cause of mosquito-borne disease in the continental United States," according to the U.S. Centers for Disease Control and Prevention website. "It is most commonly spread to people by the bite of an infected mosquito."

Most people infected with the virus do not feel sick, according to the CDC website. About 1 in 150 people, though, become seriously ill.

"Cases of WNV occur during mosquito season, which starts in the summer and continues through fall," according to the CDC website.  "There are no vaccines to prevent or medications to treat WNV in people."