Abstract
BackgroundMurray Valley encephalitis virus (MVEV) is a mosquito-borne Flavivirus (Flaviviridae: Flavivirus) which is closely related to Japanese encephalitis virus, West Nile virus and St. Louis encephalitis virus. MVEV is enzootic in northern Australia and Papua New Guinea and epizootic in other parts of Australia. Activity of MVEV in Western Australia (WA) is monitored by detection of seroconversions in flocks of sentinel chickens at selected sample sites throughout WA.Rainfall is a major environmental factor influencing MVEV activity. Utilising data on rainfall and seroconversions, statistical relationships between MVEV occurrence and rainfall can be determined. These relationships can be used to predict MVEV activity which, in turn, provides the general public with important information about disease transmission risk. Since ground measurements of rainfall are sparse and irregularly distributed, especially in north WA where rainfall is spatially and temporally highly variable, alternative data sources such as remote sensing (RS) data represent an attractive alternative to ground measurements. However, a number of competing alternatives are available and careful evaluation is essential to determine the most appropriate product for a given problem.ResultsThe Tropical Rainfall Measurement Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) 3B42 product was chosen from a range of RS rainfall products to develop rainfall-based predictor variables and build logistic regression models for the prediction of MVEV activity in the Kimberley and Pilbara regions of WA. Two models employing monthly time-lagged rainfall variables showed the strongest discriminatory ability of 0.74 and 0.80 as measured by the Receiver Operating Characteristics area under the curve (ROC AUC).ConclusionsTMPA data provide a state-of-the-art data source for the development of rainfall-based predictive models for Flavivirus activity in tropical WA. Compared to ground measurements these data have the advantage of being collected spatially regularly, irrespective of remoteness. We found that increases in monthly rainfall and monthly number of days above average rainfall increased the risk of MVEV activity in the Pilbara at a time-lag of two months. Increases in monthly rainfall and monthly number of days above average rainfall increased the risk of MVEV activity in the Kimberley at a lag of three months.
Highlights
Murray Valley encephalitis virus (MVEV; Flaviviridae: Flavivirus) is a mosquito-borne arbovirus endemic to northern Australia and Papua New Guinea
Satellite based precipitation data represent a useful data source for the analysis of spatio-temporal rainfall patterns associated with arbovirus activity, especially for larger areas
Spatially interpolated surfaces based thereon, which are expected to be inaccurate in areas where ground measurements are sparse, satellite based precipitation estimates are spatially regular and cover remote and difficult to access areas
Summary
Murray Valley encephalitis virus (MVEV; Flaviviridae: Flavivirus) is a mosquito-borne arbovirus endemic to northern Australia and Papua New Guinea. Small outbreaks of MVEV occur every few years throughout Australia, usually at the end of the wet season, between February and July [2]. Activity of MVEV occurred in epizootic regions such as the Gascoyne and the Murchison (Figure 1) and was detected 315 km north of metropolitan Perth [4] in late April 2000, representing a serious public health risk. Utilising data on rainfall and seroconversions, statistical relationships between MVEV occurrence and rainfall can be determined. These relationships can be used to predict MVEV activity which, in turn, provides the general public with important information about disease transmission risk. A number of competing alternatives are available and careful evaluation is essential to determine the most appropriate product for a given problem
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