Epidemiological study ofviral acute respiratory infections in Vietnam

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1. Background:Influenza virus infections in tropical and subtropical countries remain to be um-fear, and as new type of influenza virus occurred historically in China, influenza surveillance in Vietnam bordering on China was quite important.2. Objective:1) Epidemiological study of influenza virus infections in Vietnam as a tropical and subtropical country and early catch of new type of influenza infection by establishing of surveillance net work, 2) epidemiological study of amantadine resistant influenza viruses, 3) epidemiological study of unknown pathogenic acute respiratory syndrome, 4) basic study for future influenza vaccination program in Vietnam.3. Results:We could establish a nationwide surveillance network tied with Hanoi, Ho Chi Minh, Nha Trang, and Tay Nguyen cities in conjunction with development of laboratory human resources. High pathogenic avian influenzas H5N1 outbreak occurred in Vietnam and our counterpart institutions were contributed to control this outbreak.Acute r … More espiratory syndrome, which epidemiological background remained to be unknown, was caused by mainly influenza viruses, adenoviruses, enteroviruses, and RS virus. Influenza infections occurred throughout year with two peaks, June-September and December-February, as in other tropical and subtropical countries. These observations suggest that the time during March to May, before starting outbreak is suitable it vaccination. High prevalence of amantadine resistant H3N2 with dual mutations of HA genes (S 193F and D225N, Clade N) was found in 2005, as in Japan, USA, and Oceania.Pylogenetic analysis of individual gene segments revealed that the HA and the NA genes of the influenza A viruses evolved in as sequential way. However, the evolutionary pattern of the M gene proved to be nonlinear and was not linked with that of the HA and NA genes. Genetic drift in Hal segments, especially in antigenic sites of A/H3N2 viruses, occurred more frequently in A/H3N2 viruses than it did in A/H1N1 viruses.Thus, we can conclude that as influenza viruses circulate throughout the year, we emphasize the importance of surveillance in tropical and subtropical zones, where the emergence of new strains may be detected earlier than it is in the temperate zones. Less