Of Sandflies and Men: Environmental Factors Contributing to Kala Azar Outbreaks

Inundation map of Gedaref State in Eastern Sudan during May 2009 using the data set produced by NASA Jet Propulsion Laboratory (Wetland project) integrating PALSAR on ALOS, Advanced Microwave Scanning Radiometer on AQUA and SeaWinds on QuikSCAT.

Team Location: International Research Institute for Climate and Society, Palisades, New York

Authors:
Alex Sweeney (Columbia University)
Caitlin Reid (Columbia University)

Mentors/Advisers:
Pietro Ceccato, Ph.D. (Columbia University, International Research Institute for Climate and Society)
Madeleine Thomson, Ph.D. (Columbia University, International Research Institute)

Past/Other Contributors:
Dia Elnaiem, Ph.D. (Maryland University, Eastern Shore)
Omran F. Osma, Ph.D. (Federal Ministry of Health and the University of Khartoum, Sudan)
Doctors without Borders, Switzerland

Abstract:

Visceral Leishmaniasis (VL), also known as kala azar, is a disease caused by the parasitic protozoa called leishmania. It is transmitted by female sand flies from the Phlebotomus genus, and has initial symptoms that are similar to malaria. VL is the most serious form of leishmaniasis, and is usually fatal if left untreated. Endemic regions exist in the Indian Subcontinent and East Africa. This study focused on the Gedaref State in Eastern Sudan, which is widely affected by VL. Gedaref experiences seasonal fluctuations in incidence of leishmaniasis that typically peak from September to January.

Recent epidemics have caused hundreds of thousands of deaths; resulting in a need to understand the climatic factors associated with VL and its ecological boundaries. No concerted effort, until now, has been undertaken to understand how leishmaniasis cases are associated with climate variables on a year-to-year basis, and whether they are associated with wet or dry years. These factors include temperature, precipitation, relative humidity, and the presence of soil vertisols (more specifically black cotton soils), and Acacia-Balanite forests. Climate variability such as the El Niño Southern Oscillation (ENSO) has contributed to the sand flies seasonal activity window within this region and may cause years with larger incidences of VL. Furthermore, the emergence of VL symptoms varies depending on an individual’s immune response, causing the incubation period to be between two and six months, which makes it difficult to associate the diseases’ transmission with different environmental factors.

Cluster analyses of different environmental factors were performed using remotely sensed products over the periods of 1996-2004 and 2010-2012. NASA Earth observation products included Landsat imagery to identify water bodies and vegetation types, Moderate Resolution Imaging Spectroradiometer (MODIS) Land Surface Temperature (LST) data to determine daytime and nighttime temperature, MODIS vegetation indices (NDVI) from the University of Maryland, Tropical Rainfall Measuring Mission (TRMM) rainfall, Shuttle Radar Topography Mission (SRTM) for elevation data, and inundation data from NASA. Additionally, one non-NASA Earth observation product was used: the National Oceanic and Atmospheric Administration’s National Centers for Environmental Prediction (NOAA NCEP) relative humidity dataset. Admissions data at the village level were essential to understanding which regions in Gedaref were more susceptible to this disease.

Results from the study will be used in collaboration with the International Research Institute for Climate and Society (IRI), Doctor’s Without Borders in Switzerland, Maryland University Eastern Shore, Sudan’s Federal Ministry of Health, and the University of Khartoum. These results will allow for the development of a predictive model. This will assist with the creation of a Leishmaniasis Early Warning System for the region, which will be housed in the IRI Data Library and made available to decision-makers in Sudan.

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