Detection of reassortant orbiviruses (Wallal Serogroup) in a prototype strain isolated from a pool of biting midges (Culicoides dycei)

Queensland Institute of Medical Research, Bramston Terrace, Herston, Brisbane, Queensland 4006, Australia Genetic variation between clones selected from early passage pools of Wallal virus (Reoviridae, Orbivirus ) was investigated. The virus had been isolated in 1970 from a pool of 100 insects ( Culicoides dycei ), caught in the wild, by laboratory passage in suckling mice. Gel electrophoresis and oligonucleotide fingerprint analysis of clones indicated that multiple reassortant genotypes were present in early passages of the original isolate. The virus, previously described as the prototype strain of Wallal virus, was one of the reassortant clones. A virus recovered during reisolation from the same insect pool was genotypically and serologically distinct from the prototype strain and represents a second Wallal serotype. We have concluded that the clonal variation was due to the presence of two orbivirus serotypes in the original insect pool and that a range of reassortant viruses were generated during early passages of the material in mice. Keywords: Wallal virus, reassortant, serotype Present address: CSIRO Division of Tropical Animal Production, Private Bag No. 3, Indooroopilly, Queensland 4068, Australia. Received 29 July 1988; accepted 18 November 1988.