West Nile virus is the leading cause of mosquito-borne disease in the continental U.S. Most people who are infected with the virus are asymptomatic, but others can develop fever, and about 1 in 150 people who are infected develop a serious and sometimes fatal illness.

West Nile virus cases are on the rise across the country as mosquito season begins, according to public health officials. The Arkansas Department of Health is currently reporting fewer than five cases of the virus.

West Nile virus most often causes a mild or moderate flu-like illness, but can be more serious for those over 65 and those with underlying conditions.