Non-linear associations between meteorological factors, ambient air pollutants and major mosquito-borne diseases in Thailand

Abstract

Background

Transmission intensity for mosquito-borne diseases are highly heterogenous and multi-factorial. Understanding risk factors associated to disease transmission allow the optimization of vector control. This study sets out to understand and compare the combined anthropogenic and environmental risk factors of four major mosquito-borne diseases, dengue, malaria, chikungunya and Japanese encephalitis in Thailand.

Methods

An integrated analysis of mosquito-borne diseases, meteorological and ambient air pollutants of 76 provinces of Thailand was conducted over 2003–2021. We explored the use of generalized linear models and generalized additive models to consider both linear and non-linear associations between meteorological factors, ambient air pollutants and mosquito-borne disease incidence. Different assumptions on spatio-temporal dependence and nonlinearity were considered through province-specific and panel models, as well as different spline functions. Disease-specific model evidence was assessed to select best-fit models for epidemiological inference downstream.

Results

Analyses indicated several findings which can be generally applied to all diseases explored: (1) higher AH above mean values was positively associated with disease case counts (2) higher total precipitation above mean values was positively associated with disease case counts (3) extremely high temperatures were negatively associated with disease case counts (4) higher SO ₂ and PM _2.5 surface concentrations were negatively associated with disease case counts. However, the relationships between disease and RH, non-extreme temperatures and CO surface concentration were more mixed, with directions of associations changing across the different diseases considered.

Conclusions

This study found protective and enhancing effects of meteorological and ambient air pollutant factors on mosquito-borne diseases burdens in Thailand. Further studies should employ these factors to understand and predict risk factors associated with mosquito-borne disease transmission.

Author summary

In this study, we examined the associations between meteorological variables, ambient air pollutants and four major mosquito-borne diseases, dengue, malaria, chikungunya and Japanese encephalitis in Thailand. For the optimization of vector control, it is pertinent to understand risk factors associated to disease transmission. Given the complex transmission patterns of mosquito-borne diseases, risk factors are known to be multi-factorial in nature. Although associations between climate variables and mosquito-borne diseases have been studied extensively, the role of ambient air pollutants in mosquito-borne disease dynamics remains relatively unexplored. Recognizing that urban areas experience unique challenges related to air quality and that pollutants can have a significant impact on ecological systems, it is imperative to understand the interplay between climate variables and pollutants comprehensively. Therefore, we aim to begin addressing this gap by determining the risk factors driving multiple major mosquito-borne diseases in Thailand from 2003 to 2021. By doing so, we aim to provide valuable insights into the complex dynamics of disease transmission in urban settings, ultimately contributing to more effective public health interventions and strategies.