br Materials and Methods br

Materials and Methods
Results
Discussion Although measles is now a vaccine-preventable disease, measles remains one of the most important causes of child morbidity and mortality worldwide with the greatest burden in the youngest children (Moss and Griffin, 2006; Nandy et al., 2006; Wolfson et al., 2009). Vaccination programs have dramatically reduced the incidence of measles in developed countries, however, vaccination coverage differs widely. Globally, measles mortality decreased by 78% in the period from 2000 to 2008 (Simons et al., 2012; O\'Connor et al., 2011). In Southeast Asian countries, the estimated measles mortality has decreased dramatically and all countries except India have achieved the 90% mortality reduction target. In fact, routine measles-containing vaccine coverage in this region increased from 63% in 2000 to 75% in 2008. However, in 2008, about 9 million children born in this region were not vaccinated against measles (World Health Organization, 2010). As a result, measles still remains poorly controlled in many countries in Southeast Asia. Vietnam is a country with a high endemic level of measles and rubella, although the WHO has reported that the measles-containing vaccine coverage rate is more than 90% in this country (World Health Organization, 2010). The two-dose strategy of measles/rubella immunization has been implemented in Vietnam at the ages of 9–11months and 18months since 2006, but large-scale measles outbreaks have still occurred among children. Sniadack et al. reported on the epidemiological features of large-scale measles outbreaks in this country during 2008–2010 (Sniadack et al., 2011). However, until now, no large-scale survey on measles epidemics to characterize the viral crth2 antagonist circulating in Vietnam has yet been reported. From the end of 2013 through 2014, large outbreaks of measles among children have recurred in this country. Unfortunately, in our study presented here, we were not able to obtain detailed epidemiological information including the epidemic curve and background of the 2014 measles outbreaks in Ho Chi Minh City and neighboring provinces since the infectious disease surveillance system in Vietnam is not yet functional. During the same period, a measles outbreak also occurred in the Hanoi area which is in the Northern part of Vietnam, however, no detailed information, including the viral genotypes, is available. Very recently, we learned that genotype H1 of MV has been detected in a few cases from the 2014 outbreaks in Hanoi area (Anon., 2014). If so, different viral strains could be responsible for the 2014 measles outbreaks in the Southern and Northern parts of Vietnam. This reason might be due to geographical factors. Hanoi is located near the border of China and genotype H1 of MV is mainly circulating in China; consequently, viral strains isolated in the Hanoi area seem to be often linked to Chinese strains. The use of the molecular epidemiologic approach has contributed to understanding of the worldwide genetic diversity and transmission routes of pathogens and is considered important for supporting activities aimed at control and elimination of disease. Based on the C-terminal sequence of the N gene, the WHO currently recognizes 8 clades designated as A–H and within these clades there are 24 recognized genotypes based on sequence variation in the 450-nt of the N gene (Anon., 2012). Genotypic distribution of MV has been reported from many different regions, but there have been very few reports from Southeast Asia. A recent epidemiological study from Thailand reported that three different viral genotypes, D5, D9 and G2, were identified from 1998 to 2008 and D9 was the most frequently detected in 2008 (Pattamadilok et al., 2012). In this study, we used throat swabs obtained from suspected measles patients to detect the viral RNA and obtained a very high detection rate (100%) of MV RNA by RT-PCR. Our results reported here could be useful in efforts to control measles in Vietnam and adjacent neighboring countries. In our study based on molecular-based epidemiology of measles, we were able to confirm that the genotype D8 viruses are responsible for the measles outbreak in Vietnam in 2014. The genotype D8 virus was previously known to be prevalent in India and Europe, but has been relatively rare in Asia (Rota et al., 2011). Interestingly, although the phylogenetic analysis revealed that the Vietnamese MVs belonged to the genotype D8 clade, they formed an independent cluster within the same genotype D8 group and were located furthest away among the D8 group, suggesting their own lineage in the genomic variation of the Vietnamese viruses. Our recent study on rubella epidemics in Vietnam also showed similar findings that most of the Vietnamese virus strains responsible for rubella outbreaks formed an independent cluster within the same genotype 2B group (Pham et al., 2013). Notably, all Vietnamese measles viruses identified in this study had a unique amino acid sequence in at least 3 different sites in the N protein. The viral N protein could play an important role in viral RNA synthesis since it forms a helical nucleocapsid around the genomic RNA to form the ribonucleocapsid (Longhi et al., 2003; Griffin et al., 2012). The relationship between the virus with such unique amino acid sequences, the efficacy of the measles vaccine and the viral pathogenicity in the clinical outcome is awaited with great interest.