Abstract
BackgroundTransmission of Plasmodium vivax malaria is dependent on vector availability, biting rates and parasite development. In turn, each of these is influenced by climatic conditions. Correlations have previously been detected between seasonal rainfall, temperature and malaria incidence patterns in various settings. An understanding of seasonal patterns of malaria, and their weather drivers, can provide vital information for control and elimination activities. This research aimed to describe temporal patterns in malaria, rainfall and temperature, and to examine the relationships between these variables within four counties of Yunnan Province, China.MethodsPlasmodium vivax malaria surveillance data (1991–2006), and average monthly temperature and rainfall were acquired. Seasonal trend decomposition was used to examine secular trends and seasonal patterns in malaria. Distributed lag non-linear models were used to estimate the weather drivers of malaria seasonality, including the lag periods between weather conditions and malaria incidence.ResultsThere was a declining trend in malaria incidence in all four counties. Increasing temperature resulted in increased malaria risk in all four areas and increasing rainfall resulted in increased malaria risk in one area and decreased malaria risk in one area. The lag times for these associations varied between areas.ConclusionsThe differences detected between the four counties highlight the need for local understanding of seasonal patterns of malaria and its climatic drivers.
Highlights
Transmission of Plasmodium vivax malaria is dependent on vector availability, biting rates and parasite development
Within China, the majority of malaria cases are caused by P. vivax, with transmission occurring predominantly in central and southern areas
Four counties distributed across Yunnan Province were selected for analysis, based on a high recorded incidence of malaria and availability of meteorological data
Summary
Transmission of Plasmodium vivax malaria is dependent on vector availability, biting rates and parasite development. Transmission of malaria depends on: the availability of competent vectors, parasite development, vector biting rates and other factors Environmental factors such as temperature and rainfall have been shown to strongly influence malaria transmission and differential seasonal patterns across areas. Excessive rainfall volumes may reduce numbers due to flood waters washing away Anopheles larvae [11,12] Temperature influences both mosquito populations and the Plasmodium parasites, as the speed of both larval development and parasite maturation increases at higher temperatures [12,13], this response is nonlinear with detrimental effects on mosquito survival above a threshold temperature. The frequency of mosquito feeding increases with temperature, which has additional impacts on malaria transmission dynamics [14] These climatic dependencies drive the latitudinal and altitudinal limits on the spatial distribution of malaria, and determine seasonal patterns of malaria incidence
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