The Menglian measles viruses, together with the 2 closely related viruses, MVi/WA.AUS/12.01 and MVs/Uvbridge.GBR/19.04, should be considered as members of a newly proposed measles genotype, d11. MVi/Menglian.Yunnan.CHN/47.09 (GenBank accession nos.: N, GU440571; H, GU440576) was chosen as the reference strain because an isolate is available, it grows to high titer in cell culture, and the sequence is representative of the Menglian strains. Although designation as a genotype is not permanent until after the new genotype has been acknowledged and formally designated by WHO, the percentage sequence divergence between the N and H gene sequences of the Menglian isolates and the sequences of the reference strains exceed the recommended threshold for designation of a new measles genotype, 2.5% and 2.0%, respectively (3
). Phylogenetic analyses indicated that these viruses form a unique cluster compared with all previously characterized wild-type measles viruses. Because the Australia virus was imported from Myanmar and the sequence from the United Kingdom originated in a country adjacent to Myanmar, these sequences should be included as members of the proposed d11 genotype.
The most useful criterion for a new genotype is that it must have some epidemiologic utility for describing the transmission pathways of measles virus. The Menglian viruses responsible for the measles outbreak in China represent strains that are probably associated with endemic transmission of virus in Myanmar. When we consider the sequence of the Australia virus, we believe that the genotype d11 measles virus might have been circulating in Myanmar since 2001. The d11 sequences are easily distinguished from the sequences of viruses in other genotypes (e.g., D8, D4, H1, D5, D9, G3) that are circulating in neighboring countries. Therefore, the Menglian viruses are providing baseline genetic information about viruses endemic to Myanmar and possibly neighboring countries. The new genotype designation will enable better description of measles transmission patterns, especially in the Southeast Asian and Western Pacific regions of WHO.
Molecular epidemiologic data, when analyzed in conjunction with standard epidemiologic data, can help document viral transmission pathways, identify whether a virus is endemic or imported, and aid in case classification, thus enhancing control and elimination programs (16
). Genetic characterization of measles viruses circulating in China from 1993 through 2009 demonstrated that genotype H1 was widely distributed throughout the country and that China has a single, endemic genotype (9–11
; National Measles Laboratory database, unpub. data). However, data on the circulating genotypes in some other countries in the Southeast Asian and Western Pacific regions of WHO are limited. Further sequence analysis of measles virus strains circulating in Myanmar and neighboring countries should clarify the distribution pattern of this newly recognized genotype and may enable recognition of other new genotypes. Countries in the Western Pacific Region, including China, have committed to 2012 as the target year for measles elimination (21
). However, rapidly identifying imported measles cases and controlling spread are major challenges for achieving this goal. Enhancing measles virus surveillance to quickly identify imported cases of measles will become more critical as measles elimination goals are achieved throughout the world.