Rapid replacement of endemic measles virus genotypes.

Although vaccination campaigns have significantly reduced the number of measles cases worldwide, endemic transmission of measles virus (MV) continues to occur in several continents, including Europe. To obtain current information on measles incidence and molecular data on circulating MVs in Germany, a nationwide measles sentinel was established. Phylogenetic analysis based on the variable part of the N gene from 80 MVs isolated between November 1999 and October 2001 revealed the presence of at least six distinct MV genotypes: B3, C2, D4, D6, G2 and a new variant of D7. Both the incidence and the pattern of MV genotypes differed markedly between the former East and West Germany. In the eastern part, few measles cases, mainly caused by genotypes originating from other countries (B3, D4, G2), were detected. In the western and southern parts, genotypes C2, D6 and D7 were associated with endemic transmission. Surprisingly, the indigenous genotypes predominant during the 1990s - C2 and D6 - disappeared simultaneously over the period of observation coinciding with the emergence and the wide spread of D7 viruses. While the incidence of measles remained constant, all MVs isolated in 2001 were assigned to D7. We note that the haemagglutinin (H) sequence of D7 viruses shows distinct exchanges of certain amino acids in the stem and propeller domain compared to C2, D6 and the MV vaccine strains used. This raises the possibility of a selective advantage of D7 viruses transmitted in the presence of H-specific antibodies.