Genetic and phenotypic studies on Ross River virus variants of enhanced virulence selected during mouse passage

Entry kinetics and mouse virulence of Ross River virus mutants altered in neutralization epitopes

“…Studies with cultured cells and with mice described in this paper suggest a role for epitope b2 in some aspect of viral attachment or entry. This is consistent with studies by Meek et al (22), who showed that virulent mutants obtained by passaging avirulent RRV NB5092 in mice had changes at amino acids 212, 232, 234, and 251, which were located in neutralization epitopes in E2. As RRV NB5092 was passaged in neonatal mice, in which the immune system is immature, it is unlikely that the mutations were selected as a result of antibody pressure.…”

“…In nature, RRV exists as a number of distinct antigenic types which differ in mouse virulence (9, 12). For example, RRV T48, the prototype strain, which was isolated at Townsville in northern Queensland, is mouse virulent whereas RRV NB5092, isolated at Nelson Bay in coastal New South Wales, is mouse avirulent (10,22).The question of what properties of a virus determine its degree of virulence is important for developing effective measures for control of the virus. Two important biological properties that can affect the virulence of a virus are its growth rate and tissue tropism.…”

“…In nature, RRV exists as a number of distinct antigenic types which differ in mouse virulence (9,12). For example, RRV T48, the prototype strain, which was isolated at Townsville in northern Queensland, is mouse virulent whereas RRV NB5092, isolated at Nelson Bay in coastal New South Wales, is mouse avirulent (10,22).…”

“…These properties can be altered, at least in part, by changes in envelope proteins that are involved in receptor recognition, virus attachment and penetration, and membrane fusion to initiate the infection (for a review, see reference 41). Studies with alphaviruses, such as Sindbis virus (26,28,33,36,40), Venezuelan equine encephalitis (VEE) virus (16,19), Semliki Forest virus (13,35), and RRV (22,42), have also demonstrated that amino acid changes in envelope proteins can affect virus virulence. However, the mechanism by which these changes affect alphavirus virulence is not understood, although studies with Sindbis virus (1,5,25,33) and VEE virus (16,19) have shown an association between reduced mouse virulence and rapid penetration of BHK cells.…”

Attenuation of Chikungunya Virus Vaccine Strain 181/Clone 25 Is Determined by Two Amino Acid Substitutions in the E2 Envelope Glycoprotein

“…In contrast, the mouse isolates of the 15561/2xE2 double mutant showed no evidence of any reversion, underscoring the inherent stability advantage of multiple mutations. The stabilizing effect of multiple mutations in attenuation has been described for several other viruses, including Venezuelan equine encephalitis virus (VEEV) (7,18), Ross River virus (25), Sindbis virus (SINV) (22), and poliovirus (27).…”