CALIFORNIA LA-CROSSE ENCEPHALITIS

In the early 1960s, physicians in La Crosse County, Wisconsin, and nei ghboring areas of Minnesota were concerned with the number of children each summer who developed ''rural encephalitis.'' In 1964, Wayne Thom pson, DVM, isolated a viral agent from the postmortem brain of a 4-yea r-old victim of the malady and named the new pathogen La Crosse virus (LAC).(45) La Crosse virus was found to be an arbovirus of the Califor nia(18-20, 45) serogroup (family Bunyaviridae) transmitted by the ''tr ee-hole mosquito'' Aedes triseriatus. The virus has two types of surfa ce glycoproteins: G1 mediates attachment primarily to human (and other mammalian) cells and G2 serves attachment to mosquito (invertebrate) cells.(16, 21, 31) These glycoproteins are located on 5- to 10- nm lon g spikes protruding from the spherical lipid envelope of the La Crosse virus. The viral genome is composed of three distinct pieces of negat ive sense, single-stranded circularized RNA, termed ''S,'' ''M,'' and ''L'' segments (for small, medium and large). The M-RNA segment is a m ajor determinate of pathogenicity, encoding for the G1 and G2 surface glycoproteins.(3, 15, 16, 41)