La Crosse virus neuroinvasive disease - Missouri, 2009

La Crosse virus (LACV), a California serogroup bunyavirus, is a leading cause of pediatric arboviral encephalitis in the United States and is transmitted primarily by the eastern treehole mosquito (Aedes triseriatus). On August 7, 2009, the Missouri Department of Health and Senior Services (MDHSS) was notified of suspected LACV neuroinvasive disease in a boy aged 8 years from northwest Missouri. Laboratory testing at CDC confirmed LACV infection. An environmental inspection identified multiple vector habitats, including tree holes and discarded tires within a 300-foot radius of the patient's home. Although a median of 67 (range: 29-167) California serogroup virus neuroinvasive disease cases have been reported annually in the United States since 1964, mostly from upper Midwestern and mid-Atlantic states, this is the first reported case of LACV neuroinvasive disease in Missouri since 2002. Ae. triseriatus is found throughout Missouri and as far west as central Kansas and eastern Nebraska. Health-care providers serving this region should maintain a high clinical suspicion for LACV among patients with unexplained meningoencephalitis occurring during summer and fall.