Improvement of Disease Prediction and Modeling through the Use of Meteorological Ensembles: Human Plague in Uganda

Abstract

Climate and weather influence the occurrence, distribution, and incidence of infectious diseases, particularly those caused by vector-borne or zoonotic pathogens. Thus, models based on meteorological data have helped predict when and where human cases are most likely to occur. Such knowledge aids in targeting limited prevention and control resources and may ultimately reduce the burden of diseases. Paradoxically, localities where such models could yield the greatest benefits, such as tropical regions where morbidity and mortality caused by vector-borne diseases is greatest, often lack high-quality in situ local meteorological data. Satellite- and model-based gridded climate datasets can be used to approximate local meteorological conditions in data-sparse regions, however their accuracy varies. Here we investigate how the selection of a particular dataset can influence the outcomes of disease forecasting models. Our model system focuses on plague (Yersinia pestis infection) in the West Nile region of Uganda. The majority of recent human cases have been reported from East Africa and Madagascar, where meteorological observations are sparse and topography yields complex weather patterns. Using an ensemble of meteorological datasets and model-averaging techniques we find that the number of suspected cases in the West Nile region was negatively associated with dry season rainfall (December-February) and positively with rainfall prior to the plague season. We demonstrate that ensembles of available meteorological datasets can be used to quantify climatic uncertainty and minimize its impacts on infectious disease models. These methods are particularly valuable in regions with sparse observational networks and high morbidity and mortality from vector-borne diseases.

Identification of Risk Factors for Plague in the West Nile Region of Uganda

“…Lower elevation sites are typically warmer and drier and have sandier soils than sites above the escarpment. 11,13,16 Previous studies showed that human plague cases are more common above the escarpment than below. 11,14 Correspondingly, flea species diversity is significantly higher above the escarpment within the plague focus, compared with lower elevation sites outside the focus, and this has been hypothesized to be important for enzootic maintenance of Y. pestis.…”

“…13 Modeling of inter-annual variation showed that annual plague case counts were negatively associated with dry season rainfall (December-February) and positively associated with rainfall immediately preceding the plague season. 13 Spatial risk modeling has demonstrated that in the West Nile Region, plague risk is higher above 1,300 meters above sea level than below this value. Furthermore, covariates included in these models suggested that localities that are generally wetter, but with discontinuous rainfall, pose an increased risk for plague compared with drier areas.…”

“…10 To aid in better targeting plague prevention resources, recent research efforts in Uganda have sought to define when and where humans are most at risk for plague in the far eastern edge of this plague focus. [11][12][13][14] During August 1999-July 2011, a total of 2,409 suspect plague cases were reported from the West Nile Region of Uganda; most cases occurred during September-December, a time period that corresponds with the primary rainy season. 13 Modeling of inter-annual variation showed that annual plague case counts were negatively associated with dry season rainfall (December-February) and positively associated with rainfall immediately preceding the plague season.…”

“…[11][12][13][14] During August 1999-July 2011, a total of 2,409 suspect plague cases were reported from the West Nile Region of Uganda; most cases occurred during September-December, a time period that corresponds with the primary rainy season. 13 Modeling of inter-annual variation showed that annual plague case counts were negatively associated with dry season rainfall (December-February) and positively associated with rainfall immediately preceding the plague season. 13 Spatial risk modeling has demonstrated that in the West Nile Region, plague risk is higher above 1,300 meters above sea level than below this value.…”

“…Because previous work showed that human plague cases occur seasonally and are often associated with rainfall, we selected our sampling periods to occur within each of the four seasons. 13 Session one (June 27-July 11, 2012) was conducted during the interval season that is generally cool with variable rainfall. Session two (September 25-October 9, 2012) was conducted during the cool, primary rainy season when most yearly rainfall occurs.…”