Epidemiology and Infection

Research Article

Antigenic relationship of West Nile strains by titre ratios calculated from cross-neutralization test results

N. K. Blackburna1, D. L. Thompsona1 and P. G. Juppa1

a1 Department of Virology, University of the Witwatersrand and Arbovirus Unit, National Institute for Virology, Sandringham 2131, Johannesburg


The antigenic relationship of ten South African West Nile isolates, the South African prototype virus H442, the Egyptian strain EG101 and the Indian strain G2266 were compared using titre ratios. The titre ratios or ‘R’ values were calculated from heterologous and homologous neutralization titres and expressed as a percentage.

Substantial antigenic differences were demonstrated between the South African prototype strain and the majority of the recently obtained South African isolates, seven of which were fairly closely related and possibly form a distinct antigenic sub-set. The recent isolates also differed from the Egyptian and Indian West Nile isolates. The heterologous results between the South African West Nile strains and the Indian strain G2266 suggest that prior infection with an Indian West Nile virus would give poor protection against the South African viruses, whereas the reverse would not be so.

(Accepted March 13 1987)