Public Health Director Eric Whitaker says a 16-year-old Macoupin County boy became ill August 4 with a headache, fever, stiff neck and muscle aches. He recovered without hospitalization.
Health officials say the boy had returned from a trip to Mexico before becoming ill, so the location of transmission was unclear. He recovered without hospitalization.
The department's laboratory tests confirmed the illness was caused by the mosquito-borne illness that last year sickened 884 and killed 66 in Illinois.
The first human case of the year was announced Tuesday, involving a 69-year-old Champaign County man who remains hospitalized.