Diagnosis of acute deer tick virus encephalitis.

Background: Deer tick virus (DTV) is a tick-borne flavivirus that has only recently been appreciated as a cause of viral encephalitis. We describe the clinical presentation of a patient who had DTV encephalitis diagnosed before death and survived for 8 months despite severe neurologic dysfunction.

Methods: Diagnosis was made from a cerebrospinal fluid specimen, using a flavivirus-specific polymerase chain-reaction assay followed by sequence confirmation, and the phylogeny was analyzed. Serologic testing, including plaque reduction neutralization testing, was also performed.

Results: Molecular analysis indicated that the virus was closely related to 2 strains of DTV that had been detected in Ixodes scapularis ticks from Massachusetts in 1996 and in the brain of a patient from New York in 2007.

Conclusions: DTV encephalitis should be considered in the differential diagnosis of encephalitis in geographic areas that are endemic for Lyme disease.