After 7 years of silence, La Crosse neuroinvasive disease reported in Missouri

CDC. MMWR. 2010;59:869-871.

Last year, Missouri reported its first case of La Crosse virus neuroinvasive disease since 2002. According to the CDC, the virus — a California serogroup bunyavirus — is the leading cause of arboviral encephalitis in the U.S. among children. It is transmitted primarily by the Aedes triseriatus, an eastern treehole mosquito.

Since 1964, in the United States, a median of 67 cases of California serogroup virus neuroinvasive disease have been reported annually. Reports usually originate from the Upper Midwest and Mid-Atlantic states, but on July 29, 2009, an 8-year-old boy from Missouri presented to the ED with headache, fatigue, nausea, vomiting and abdominal pain.

After several examinations, the patient was tested for West Nile, eastern equine encephalitis, western equine encephalitis, St. Louis encephalitis and California serogroup viruses. The results demonstrated positive immunoglobulin M and IgG against California serogroup viruses in serum and cerebrospinal fluid. The patient recovered with no neurologic abnormalities.

According to the researchers, an examination conducted at the patient’s home revealed 14 tree holes and eight discarded tires, one containing water and mosquito larvae.

“Ae. triseriatus is found throughout Missouri and as far west as central Kansas and eastern Nebraska,” the researchers wrote.

To date, this disease has not been reported in Kansas or Nebraska, but the researchers noted that it may have been under-recognized or underreported in this region. In Missouri, however, 13 cases were reported between 1973 and 2001.

“Health care providers serving this region should maintain a high clinical suspicion for La Crosse virus among patients with unexplained meningoencephalitis occurring during summer and fall,” the researchers wrote.

According to the CDC, any cases of suspected or confirmed La Crosse virus disease should be reported to state and local public health departments promptly. In addition, confirmatory serologic testing should be performed in a reference laboratory to differentiate La Crosse virus from other California serogroup viruses. There currently are no FDA-cleared immunoassays available for the detection of La Crosse virus-specific IgM or IgG antibodies in serum or cerebrospinal fluid, according to the researchers.