Dengue virus infection has been counted among emerging and re-emerging diseases because of (1) the increasing number of patients, (2) the expansion of epidemic areas, and (3) the appearance of severe clinical manifestation of dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS), which is often fatal if not properly treated. In the meantime, there are no effective dengue control measures: a dengue vaccine is still under development and vector control does not provide a long-lasting effect. In order to obtain direct evidence for the virulent virus theory concerning the pathogenesis of DHF/DSS, type 2 dengue virus strains isolated from patients with different clinical severities in the same epidemic area in northeast Thailand, during the same season, were comparatively sequenced. The result revealed a DF strain specific amino acid substitution from I to R in the PrM, and a DSS strain specific amino acid substitution from D to G in the NS1 gene regions, which could significantly alter the nature of these proteins. Moreover, DF strain specific nucleotide substitutions in the 3' noncoding region were predicted to alter its secondary structure. These amino acid and nucleotide substitutions in other strains isolated in different epidemic areas during other seasons, together with their biological significance, remain to be confirmed. In order to innovate dengue vector control, field tests were carried out in dengue epidemic areas in Vietnam to examine the efficacy of Olyset Net screen, which is a wide-mesh net made of polyethylene thread impregnated with permethrin. The results show that Olyset Net (1) reduced the number of principal dengue vector species, Aedes aegypti, (2) interrupted the silent transmission of dengue viruses and (3) was highly appreciated by the local people as a convenient and comfortable vector control method. This encouraging evaluation of the Olyset Net screen should be confirmed further by other tests under different settings.
PIP: The number of dengue hemorrhagic fever cases reported to the World Health Organization increased sharply in the 1985-90 period. This expansion was associated with socioeconomic growth in tropical countries and increases in the importance of migration as a mode of dengue transmission. To find direct evidence for the virulent virus theory, the author investigated dengue virus infection in northeastern Thailand and performed comparative sequence analysis of virus strains collected from individuals with different clinical manifestations. The four dengue type 2 strains possessed the highest homology to the New Guinea C strain. As the sequences diverged from the standard, the clinical severity of the disease was reduced. The biologic significance of the amino acid and nucleotide substitutions observed requires further analysis. In another study, the author evaluated the impact of vector control with the permethrin-impregnated Olyset mesh screen in northern Viet Nam's Hai Hung Province in 1994. The net provided significant protection against the principal dengue vector mosquito, Aedes aegypti, and the antibody rate remained low (6.4%) during the epidemic rainy season. Net acceptors agreed that this method of vector control is simple, convenient, and effective.