Historically, most cases of LAC encephalitis occur in the upper Midwestern states (Minnesota, Wisconsin, Iowa, Illinois, Indiana, and Ohio); however, more cases are being reported from states in the mid-Atlantic (West Virginia, Virginia, and North Carolina) and southeastern (Alabama and Mississippi) regions of the United States.
LAC encephalitis is most commonly seen in the hardwood deciduous forest areas of the upper Midwestern United States (Minnesota, Wisconsin, Iowa, Illinois, Indiana, and Ohio) and in the Appalachian region of the United States (West Virginia, North Carolina, Tennessee, and Virginia).
In the United States about 75 cases of LAC encephalitis are reported annually to the CDC.
The incubation period for LAC encephalitis is approximately 2 to 7 days with the disease typically occurring during the summertime.
Diagnosis of LAC encephalitis in animals is not done clinically, but may be done to monitor the virus in wildlife.
Human cases of LAC encephalitis in Tennessee and North Carolina have increased above endemic levels during 1997 to 1999 and may represent an expansion of a new southeastern endemic focus.
In recent years, LAC encephalitis activity has increased in West Virginia, which has had more recorded cases than any other state, accounting for more than half of cases reported from 1996 to 1999 (2).
From 1963 to 1996, nine cases of pediatric LAC encephalitis were reported in Tennessee (1).
In contrast to Tennessee, approximately three cases per year of LAC encephalitis have been reported from western North Carolina from 1977 to 1995 (4,5).
Active surveillance for human LAC encephalitis cases and virus-infected mosquitoes has been conducted in eastern Tennessee since 1997.