Report

Dengue diversity across spatial and temporal scales: Local structure and the effect of host population size

+ See all authors and affiliations

Science  24 Mar 2017:
Vol. 355, Issue 6331, pp. 1302-1306
DOI: 10.1126/science.aaj9384

You are currently viewing the abstract.

View Full Text

Estimating transmission chains for dengue

Dengue virus (DENV) causes a large number of asymptomatic infections, so surveillance captures only a fraction of cases. Salje et al. developed a method for identifying the number of transmission chains of DENV from sequence data and serology. They found that sequential transmission of DENV typically occurs between households in the same neighborhood. Within high-density urban localities, such as Bangkok, there are surprisingly few transmission chains. This results in epidemic spikes within a regional background of endemicity. Large urban settings may thus act as a source of diverse viruses that can be transported elsewhere.

Science, this issue p. 1302

Abstract

A fundamental mystery for dengue and other infectious pathogens is how observed patterns of cases relate to actual chains of individual transmission events. These pathways are intimately tied to the mechanisms by which strains interact and compete across spatial scales. Phylogeographic methods have been used to characterize pathogen dispersal at global and regional scales but have yielded few insights into the local spatiotemporal structure of endemic transmission. Using geolocated genotype (800 cases) and serotype (17,291 cases) data, we show that in Bangkok, Thailand, 60% of dengue cases living <200 meters apart come from the same transmission chain, as opposed to 3% of cases separated by 1 to 5 kilometers. At distances <200 meters from a case (encompassing an average of 1300 people in Bangkok), the effective number of chains is 1.7. This number rises by a factor of 7 for each 10-fold increase in the population of the “enclosed” region. This trend is observed regardless of whether population density or area increases, though increases in density over 7000 people per square kilometer do not lead to additional chains. Within Thailand these chains quickly mix, and by the next dengue season viral lineages are no longer highly spatially structured within the country. In contrast, viral flow to neighboring countries is limited. These findings are consistent with local, density-dependent transmission and implicate densely populated communities as key sources of viral diversity, with home location the focal point of transmission. These findings have important implications for targeted vector control and active surveillance.

View Full Text