High genetic diversity of measles virus, World Health Organization European Region, 2005-2006

Abstract

During 2005-2006, nine measles virus (MV) genotypes were identified throughout the World Health Organization European Region. All major epidemics were associated with genotypes D4, D6, and B3. Other genotypes (B2, D5, D8, D9, G2, and H1) were only found in limited numbers of cases after importation from other continents. The genetic diversity of endemic D6 strains was low; genotypes C2 and D7, circulating in Europe until recent years, were no longer identified. The transmission chains of several indigenous MV strains may thus have been interrupted by enhanced vaccination. However, multiple importations from Africa and Asia and virus introduction into highly mobile and unvaccinated communities caused a massive spread of D4 and B3 strains throughout much of the region. Thus, despite the reduction of endemic MV circulation, importation of MV from other continents caused prolonged circulation and large outbreaks after their introduction into unvaccinated and highly mobile communities.

Figure 1

Phylogenetic tree showing representative genotype D6 strains identified in Europe before 2005, strains exported from Europe to other continents (source of exportation is shown in brackets), and the D6 variants that were dominant in Europe during 2005 (D6–2000) and 2006 (D6–2005). The phylogenetic tree was calculated on the basis of the 450 nt that code for the C-terminus of the MV N protein, by using MEGA 3.1 software and the neighbor-joining method (500 bootstraps). Genetic distances are represented as numbers of nucleotide differences between strains. Measles virus strains were named according to World Health Organization nomenclature: MVi/City of isolation.Country/epidemiologic week.year of isolation(/isolate number). Sequences obtained from RNA extracted from isolates (MVi) or clinical material (MVs) were distinguished. GenBank accession numbers are also shown for each strain.

Figure 2

Two main variants, D6–2000 and D6–2005, of D6 identified in Europe during 2005–2006. Tree calculation and measles virus nomenclature are as delineated in Figure 1.

Figure 3

Four different genetic groups of genotype D4 identified in Europe during 2005–2006 and their closest relatives (in italics) identified on other continents. Tree calculation and measles virus nomenclature are as delineated in Figure 1.

Figure 4

Genotype B3 variants identified in Europe during 2005–2006 and some closely related strains identified on other continents (in italics). Tree calculation and measles virus nomenclature are as delineated in Figure 1.