The molecular epidemiology of mumps virus.

The molecular epidemiology of MuV is characterized by the co-existence of 10 (or more) distinct genotypes named A-J based on the nucleotide sequence of the SH gene. MuV show distinct geographic clustering. More than one genotype may circulate simultaneously in a geographic region. Limited data suggest redistribution of genotypes to occur over time. The selective forces remain speculative. Currently used vaccine strains belong to different genotypes. Some MuV genotypes (C, D, H, J) and vaccine strains (Urabe Am9) have been associated with enhanced neurovirulence. Also, reduced cross-neutralization capacity has been observed between genotype A and genotypes C and D. At present vaccine failure cannot be attributed to this phenomenon. Strain redistribution may lead to the emergence of new MuV strains with enhanced neurovirulence or reduced cross-neutralization capacity with current vaccine strains. Close monitoring of the genotype distribution of MuV and genotype-specific population immunity is needed in the vaccine era.