Abstract

A favorable climatic condition for transmission of malaria prevails in Kokrajhar district throughout the year. A sizeable part of the district is covered by forest due to which dissimilar dynamics of malaria transmission emerge in forest and non-forest areas. Observed malaria incidence rates of forest area, non-forest area and the whole district over the period 2001-2010 were considered for analyzing temporal correlation between malaria incidence and climatic variables. Associations between the two were examined by Pearson correlation analysis. Cross-correlation tests were performed between pre-whitened series of climatic variable and malaria series. Linear regressions were used to obtain linear relationships between climatic factors and malaria incidence, while weighted least squares regression was used to construct models for explaining and estimating malaria incidence rates. Annual concentration of malaria incidence was analyzed by Markham technique by obtaining seasonal index. Forest area and non-forest area have distinguishable malaria seasons. Relative humidity was positively correlated with z malaria incidence, while temperature series were negatively correlated with non-forest malaria incidence.There was higher seasonality of concentration of malaria in the forest area than non-forest area. Significant correlation between annual changes in malaria cases in forest area and temperature was observed (coeff=0.689, p=0.040).Separate reliable models constructed for forecasting malaria incidence rates based on the combined influence of climatic variables on malaria incidence in different areas of the district were able to explain substantial percentage of observed variability in the incidence rates (R2adj=45.4%, 50.6%, 47.2%; p< .001 for all). There is an intricate association between climatic variables and malaria incidence of the district. Climatic variables influence malaria incidence in forest area and non-forest area in different ways. Rainfall plays a primary role in characterizing malaria incidences in the district. Malaria parasites in the district had adapted to a relative humidity condition higher than the normal range for transmission in India. Instead of individual influence of the climatic variables, their combined influence was utilizable for construction of models.

Highlights

  • Association between malaria incidence and climatic behavior has been established through various malaria studies conducted for different parts of the world

  • Malaria incidence rate (MIR) for the whole district, forest area and non-forest area was calculated by the formulamalaria of cases positive cases tested for malaria

  • None of the climatic variable was found to bear a significant correlation with monthly malaria incidence rate of the whole district (DMIR) at 5% significance level, only the mean and morning relative humidity bore a significant correlation at 10% significance level

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Summary

Introduction

Association between malaria incidence and climatic behavior has been established through various malaria studies conducted for different parts of the world. Several studies have revealed that there may be influence of climatic variables on malaria transmission in either way. During 1988-1999, in Zimbabwe, inter-annual variations in average temperature, rainfall and vapour pressure were found to have strong positive association with malaria incidence while maximum and minimum temperature were acting in opposite way (Musawenkoi et al, 2006). Climate variability was found to play an important role in initiating malaria epidemics in the East African highlands (Zhou et al, 2004). Though malaria had been found to be associated with some socio-economic factors (Niringiye & Douglason, 2010; Sheila et al, 2009), climatic factors are primary ones as these can play direct role in the development of malaria mosquitoes and the www.ccsenet.org/gjhs

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