Molecular epidemiology of measles virus in Taiwan in 2010-2011: the common genotype changed from H1 to D9 and the first appearance of D4.

Measles has been controlled effectively in some countries because of high coverage rates with an effective vaccine. However, measles outbreaks still occasionally occur in areas with high vaccine coverage as a result of imported transmission. To identify the sources of measles infection and to determine whether measles cases are part of a single outbreak or due to multiple importations, measles virus (MV) genotyping is required and plays an important role in MV elimination. In Taiwan, genotype H1 of MV was detected most frequently before 2009. From 2006 to 2011, 47 of 48 genotype H1 cases were associated with the imported cases, indicating that genotype H1 was not an endemic genotype in Taiwan after 2006. The distribution of the other genotypes (D3, D4, D5, D8, D9, and G3) detected during 2006-2011 varied by year. Taiwan has a pattern of measles genotypes that is consistent with the elimination of MV and with the absence of endemic genotypes. In this study, the genotypes of 40 cases of MV detected during 2010-2011 were investigated and analyzed. In 2010, the most common genotype changed from H1 (3/40) to D9 (35/40). In 2011, genotype H1 was not detected, and genotype D4 first appeared and was imported from Europe. The dynamic change of detected genotypes of MV in Taiwan is influenced by the activity of a measles control program in WHO regions. This study emphasizes that global synchronous elimination is important for an individual country or area to maintain free from MV.