Genetics, infectivity and virulence of California serogroup viruses

Abstract

The California serogroup of viruses includes 14 viruses which take their name from California encephalitis virus, the prototype of the serogroup, which was isolated in California in the 1950s (Hammon and Reeves, 1952). This serogroup is part of the Bunyauirus genus within the family Bunyaviridae (Gonzalez-Scarano and Nathanson, 1990; Kolakofsky, 1991; Whitman and Shope, 1962). La Crosse virus, the most medically significant member of the California serogroup, was isolated in 1964 from a fatal case of encephalitis diagnosed in La Crosse, Wisconsin (Thompson et al., 1965). Although California encephalitis virus was initially reported in association with a few cases of encephalitis, it is not an important human pathogen. On the other hand, La Crosse virus is a common cause of encephalitis in the pediatric age group, with an average of about 75 reported cases of encephalitis each year (Kappus et al., 1983). In years when other arboviruses are not epidemic, La Crosse virus is the most important cause of arbovirus encephalitis in the United States. The virus is estimated to cause more than 100,000 inapparent infections annually which are concentrated in the midwest (Grimstad et al., 1984), which is the principal habitat of Aedes triseriatus, its major mosquito vector. Bunyavirions are roughly spherical particles about 100 nm in diameter consisting of a lipid envelope containing nucleocapsids representing the three different RNA species (L segment, 6.8 kb; M segment, 4.5 kb; and S segment, 0.9 kb) which comprise the negative-sense genome (Elliott, 1990; Gonzalez-Scarano and Nathanson, 1990). The viral envelope contains two glycoproteins, Gl and G2, and