The Role of Climate Variability in the Spread of Malaria in Bangladeshi Highlands

Ubydul Haque,Ashraf M Dewan,Taro Yamamoto,Hans J Overgaard,Masahiro Hashizume,Gregory E Glass,Erika Martins Braga

doi:10.1371/journal.pone.0014341

Abstract

BackgroundMalaria is a major public health problem in Bangladesh, frequently occurring as epidemics since the 1990s. Many factors affect increases in malaria cases, including changes in land use, drug resistance, malaria control programs, socioeconomic issues, and climatic factors. No study has examined the relationship between malaria epidemics and climatic factors in Bangladesh. Here, we investigate the relationship between climatic parameters [rainfall, temperature, humidity, sea surface temperature (SST), El Niño-Southern Oscillation (ENSO), the normalized difference vegetation index (NDVI)], and malaria cases over the last 20 years in the malaria endemic district of Chittagong Hill Tracts (CHT).Methods and Principal FindingsMonthly malaria case data from January 1989 to December 2008, monthly rainfall, temperature, humidity sea surface temperature in the Bay of Bengal and ENSO index at the Niño Region 3 (NIÑO3) were used. A generalized linear negative binomial regression model was developed using the number of monthly malaria cases and each of the climatic parameters. After adjusting for potential mutual confounding between climatic factors there was no evidence for any association between the number of malaria cases and temperature, rainfall and humidity. Only a low NDVI was associated with an increase in the number of malaria cases. There was no evidence of an association between malaria cases and SST in the Bay of Bengal and NIÑO3.Conclusion and SignificanceIt seems counterintuitive that a low NDVI, an indicator of low vegetation greenness, is associated with increases in malaria cases, since the primary vectors in Bangladesh, such as An. dirus, are associated with forests. This relationship can be explained by the drying up of rivers and streams creating suitable breeding sites for the vector fauna. Bangladesh has very high vector species diversity and vectors suited to these habitats may be responsible for the observed results.

Highlights

Malaria is the most important tropical and parasitic disease in the world
It seems counterintuitive that a low normalized difference vegetation index (NDVI), an indicator of low vegetation greenness, is associated with increases in malaria cases, since the primary vectors in Bangladesh, such as An. dirus, are associated with forests
Bangladesh has very high vector species diversity and vectors suited to these habitats may be responsible for the observed results

Summary

Introduction

In 2008, there were an estimated 243 million cases of malaria, the vast majority of cases (85%) occurring in the African Region. In 2008, malaria morbidity and mortality in Bangladesh were recorded as 84,690 and 154, respectively [3]. Malaria is endemic in 13 northern and eastern districts of Bangladesh along the border with India and Myanmar, with 90% of morbidity and mortality reported from three hill districts (Rangamati, Bandarban and Khagrachari) (Figure 1). Malaria is a major public health problem in Bangladesh, frequently occurring as epidemics since the 1990s. No study has examined the relationship between malaria epidemics and climatic factors in Bangladesh. We investigate the relationship between climatic parameters [rainfall, temperature, humidity, sea surface temperature (SST), El Nino-Southern Oscillation (ENSO), the normalized difference vegetation index (NDVI)], and malaria cases over the last 20 years in the malaria endemic district of Chittagong Hill Tracts (CHT)

Methods

Results

Discussion

Conclusion