Variation in Orbiviruses

Queensland Institute of Medical Research, Bramston Terrace, Herston 4006, Brisbane, Australia Introduction. The name orbiviruses was proposed by Borden et al. (1971) to describe a group of arthropod-borne viruses which, by their physico-chemical properties and characteristic appearance by electron microscopy, were sufficiently distinct to form a new taxonomic group. Unlike other arboviruses, these viruses were either less susceptible or resistant to the action of diethyl ether or deoxycholate. The name reflected the especially large doughnut-shaped capsomeres seen on the surface of virus particles by electron microscopy. The orbiviruses included pathogenic agents of man (Colorado tick fever), domestic animals (bluetongue of sheep and African horse sickness), native animals (epizootic haemorrhagic disease of deer) and many other viruses not yet linked with disease. Verwoerd (1969) isolated double-stranded RNA from purified bluetongue virus and further characterization showed that it consisted of ten fragments similar to but not identical with double-stranded RNA segments isolated from reovirus (Verwoerd et al. 1970).