Molecular evolution of measles viruses circulated in Taiwan 1992-2008

Abstract

Genetic analyses of viral samples from 74 laboratory confirmed measles cases occurring in Taiwan during 1992-2008 identified six viral genotypes D3, D5, D9, G2, H1 and H2. The most frequently detected genotype, H1, was associated with outbreaks in 1994 and 2002, and was the likely indigenous genotype in 1992. In response to the outbreaks, two catch-up campaigns were launched and a routine second dose of measles, mumps, and rubella vaccine at entry to elementary school was introduced. The vaccination campaigns successfully reduced the number of measles cases in Taiwan, and many of the more recent cases can be traced to importations, primarily from other Asian countries. A number of measles genotypes which were associated with outbreaks in other Asian countries were detected among the more recent cases. The more recent genotype H1 viruses had sequences that were identical to those currently circulating in China or associated with international importation of virus.

Figure 1

Measles surveillance and vaccination in Taiwan, 1968-2008. Figure shows numbers of reported cases (black bars) and laboratory confirmed cases (lines) by year. The dates of introduction of measles vaccination and changes in the measles vaccination program, including campaigns, are indicated by the text and arrows. The year when measles became a reportable disease was 1985. The year when routine laboratory confirmation started was 1991, and the year when laboratory confirmation required was 2000.

Figure 2

Phylogenetic analysis of the carboxyl terminal 456 nucleotides of the N gene sequences from measles virus cases in Taiwan, 1992-2008. The dendrogram was created with MEGA 4.1 by the neighbor-joining method with 1000 bootstrap replicates. The asterisks indicate cases imported from foreign countries. Several sequences with highest nucleotide blast search from GenBank (shown by italic) are also included. The reference strains recommended by WHO (shown by bold italic) also included for comparison. The tree on 2A shows all sequences with the part of the tree showing all genotypes except genotypes H1 and H2 expanded for easier viewing on 2B. Genotypes detected in Taiwan are indicated on the tree of 2B.

Figure 3

Phylogenetic analysis of the 456 nts coding for the COOH terminus of the N protein of measles viruses detected in Taiwan, 1992-2008, highlighting the sequences in genotype H1. The dendrogram was created with MEGA 4.1 by the neighbor-joining method with 1000 bootstrap replicates. The asterisks indicate viruses detected from imported cases. Several closely related sequences with the highest nucleotide BLAST scores from GenBank are also included (italic). The reference strains recommended by WHO also included for comparison (bold italic). The tree in figure 3A shows all sequences with the part of the tree showing only genotypes H1 and H2 expanded for easier viewing in figure 3B. The two previously described clusters of genotype H1 [25], are represented by MVi/Shanxi.PRC/13.02/1 (DQ356858) for cluster 1 and MVi/Hunan.PRC/18.95/18 (DQ356791) and MVi/Hunan.PRC/15.95/9 (DQ356792) for cluster 2.