El Nino and the dynamics of vectorborne disease transmission

The objective of the study was to investigate the relationship between repo rted incidence of dengue fever and El Nino southern oscillation (ENSO) in 1 4 island nations of the South Pacific. Using a mixed ecological study desig n, we calculated correlations between annual averages of the southern oscil lation index (SOI), local temperature and rainfall, and dengue fever. We al so calculated temporal correlations between monthly reports of dengue fever cases on different islands. There were positive correlations between SOI a nd dengue in 10 countries. In five of these (including all of the larger is lands) there were also positive correlations between SOI and estimates of l ocal temperature and/or rainfall. There were temporal correlations between monthly reports of dengue cases within two groups of countries. Climate cha nges associated with ENSO may trigger an increase in dengue fever transmiss ion in larger, more populated islands where the disease is endemic. There w as also evidence of propagation of infection from larger islands to smaller neighbors. Unlike the initiation of epidemics, this transfer between islan ds appears to be independent of interannual climate variations, pointing to the importance of modulating factors in dengue transmission such as popula tion density and travel. In the future, models of the impact of climate cha nge must attempt to account for these factors.