Classification: ICD-9 062.5; ICD-10 A83.5
Syndromes and synonyms: California encephalitis, Jamestown Canyon encephalitis, La Crosse encephalitis.
Agents: Spherical, enveloped, negative sense RNA viruses forming a subgroup of the Bunyaviridae family. In the Americas, human pathogens belonging to the group are Guaroa virus (GROV), Jamestown Canyon virus (JCV), LaCrosse virus (LACV), and snowshoe hare virus (SSHV). Those reported to cause human disease in Europe or Asia are Inkoo virus (INKV), Tahyna virus (TAHV), and SSHV.
Reservoir: Small wild mammals such as rodents, snowshoe hares, deer and vector mosquitoes (venereal and transovarian transmission occur). Dayfeeding chipmunks and squirrels are the principal amplifying hosts of LACV, as the main vector (Aedes triseriatus) only bites in daytime. For this reason, night-feeding small mammals are rarely infected with LACV. The white-tailed deer is the main amplifying host for JCV (horses can also be an amplifying host). Snowshoe hares and the arctic ground squirrel are the amplifying hosts of SSHV.
Vector: Mosquitoes, primarily Aedes and Ochlerotatus spp., secondarily Anopheles spp. Ae. triseriatus (eastern treehole mosquito) is the most important vector of LACV in the USA. LACV is abundant in forests with oak trees (basal holes are important breeding sites) and hickory hardwoods drained by rapid streams. Different species of cold-tolerant mosquitoes serve as vectors for JCV and SSHV.
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