Seasonal patterns of dengue incidence in Thailand across the urban-rural gradient

Abstract

In Southeast Asia, endemic dengue follows strong spatio-temporal patterns with major epidemics occurring every 2-5 years. However, important spatio-temporal variation in seasonal dengue epidemics remains poorly understood. Using 13 years (2003-2015) of dengue surveillance data from 926 districts in Thailand and wavelet analysis, we show that rural epidemics lead urban epidemics within a dengue season, both nationally and within health regions. However, local dengue fade-outs are more likely in rural areas than in urban areas during the off season, suggesting rural areas are not the source of viral dispersion. Simple dynamic models show that stronger seasonal forcing in rural areas could explain the inconsistency between earlier rural epidemics and dengue “over wintering” in urban areas. These results add important nuance to earlier work showing the importance of urban areas in driving multi-annual patterns of dengue incidence in Thailand. Feedback between geographically linked locations with markedly different ecology is key to explaining full disease dynamics across urban-rural gradient.

Envisioning urban environments resilient to vector-borne diseases: a protocol to study dengue in Vietnam

“…Mosquito larvae graze on aquatic microbial growth, which may vary considerably in quality and is driven largely by autochthonous inputs of terrestrial leaf litter detritus [22]. In areas where electricity and water supplies are unreliable, households may store water, increasing the likelihood of colonization by Aedes mosquitoes [23]. Due to variations in the reliability of these municipal services, the presence of artificial container habitats, and human population density, in the example of Vietnam the risk of exposure to DENV varies with human land-use gradients [24], socioeconomic gradients [25], and the built environment [26].…”