Abstract
BackgroundEnvironmental factors play a major role in transmission of malaria given their relationship to both the development and survival of the mosquito and parasite. The associations between environmental factors and malaria can be used to inform the development of early warning systems for increases in malaria burden. The objective of this study was to assess temporal relationships between rainfall, temperature and vegetation with malaria morbidity across three different transmission settings in Uganda.MethodsTemporal relationships between environmental factors (weekly total rainfall, mean day time temperature and enhanced vegetation index series) and malaria morbidity (weekly malaria case count data and test positivity rate series) over the period January 2010–May 2013 in three sites located in varying malaria transmission settings in Uganda was explored using cross-correlation with pre-whitening. Sites included Kamwezi (low transmission), Kasambya (moderate transmission) and Nagongera (high transmission).ResultsNagongera received the most rain (30.6 mm) and experienced, on average, the highest daytime temperatures (29.8 °C) per week. In the study period, weekly TPR and number of malaria cases were highest at Kasambya and lowest at Kamwezi. The largest cross-correlation coefficients between environmental factors and malaria morbidity for each site was 0.27 for Kamwezi (rainfall and cases), 0.21 for Kasambya (vegetation and TPR), and −0.27 for Nagongera (daytime temperature and TPR). Temporal associations between environmental factors (rainfall, temperature and vegetation) with malaria morbidity (number of malaria cases and TPR) varied by transmission setting. Longer time lags were observed at Kamwezi and Kasambya compared to Nagongera in the relationship between rainfall and number of malaria cases. Comparable time lags were observed at Kasambya and Nagongera in the relationship between temperature and malaria morbidity. Temporal analysis of vegetation with malaria morbidity revealed longer lags at Kasambya compared to those observed at the other two sites.ConclusionsThis study showed that temporal associations between environmental factors with malaria morbidity vary by transmission setting in Uganda. This suggests the need to incorporate local transmission differences when developing malaria early warning systems that have environmental predictors in Uganda. This will result in development of more accurate early warning systems, which are a prerequisite for effective malaria control in such a setting.
Highlights
Environmental factors play a major role in transmission of malaria given their relationship to both the development and survival of the mosquito and parasite
The study showed that temporal associations between environmental factors with malaria morbidity varied by transmission setting (Table 2)
Longer time lags were observed in the relationship between rainfall and number of malaria cases at Kamwezi and Kasambya, 11–12 weeks, compared to Nagongera that showed a lag of 3 weeks
Summary
Environmental factors play a major role in transmission of malaria given their relationship to both the development and survival of the mosquito and parasite. The objective of this study was to assess temporal relationships between rainfall, temperature and vegetation with malaria morbidity across three different transmission settings in Uganda. Uganda is a relatively humid equatorial country local differences in rainfall and temperature are caused by the topography, prevailing winds, and water bodies [4]. Uganda has a relatively high altitude, 1300–1500 m above sea level, and a mean annual temperature that ranges from 16 °C in the southwest to 30 °C in the northeast and 25 °C in rest of the country [5]. Vegetation is varied, with tropical rain forests in the south, wooded savanna in central Uganda and semidesert conditions in the north [6]
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