A GEOGRAPHIC INFORMATION-SYSTEM ON THE POTENTIAL DISTRIBUTION AND ABUNDANCE OF FASCIOLA-HEPATICA AND FASCIOLA-GIGANTICA IN EAST-AFRICA BASED ON FOOD AND AGRICULTURE ORGANIZATION DATABASES

An adaptation of a previously developed climate forecast computer mode l and digital agroecologic database resources available from FAO for d eveloping countries were used to develop a geographic information syst em risk assessment model for fasciolosis in East Africa, a region wher e both F. hepatica and F. gigantica occur as a cause of major economic losses in livestock. Regional F: hepatica and F. gigantica forecast i ndex maps were created. Results were compared to environmental data pa rameters, known life cycle micro-environment requirements and to avail able Fasciola prevalence survey data and distribution patterns reporte d in the literature for each species (F. hepatica above 1200 m elevati on, F: gigantica below 1800 m, both at 1200-1800 m). The greatest risk , for both species, occurred in areas of extended high annual rainfall associated with high soil moisture and surplus water, with risk dimin ishing in areas of shorter wet season and/or lower temperatures. Arid areas were generally unsuitable (except where irrigation, water bodies or floods occur) due to soil moisture deficit and/or, in the case of F. hepatica, high average annual mean temperature >23 degrees C. Regio ns in the highlands of Ethiopia and Kenya were identified as unsuitabl e for F: gigantica due to inadequate thermal regime, below the 600 gro wing degree days required for completion of the life cycle in a single year. The combined forecast index (F: hepatica+F. gigantica) was sign ificantly correlated to prevalence data available for 260 of the 1220 agroecologic crop production system zones (CPSZ) and to average monthl y normalized difference vegetation index (NDVI) values derived from th e advanced very high resolution radiometer (AVHRR) sensor on board the NOAA polar-orbiting satellites. For use in Fasciola control programs, results indicate that monthly forecast parameters, developed in a GIS with digital agroecologic zone databases and monthly climate database s, can be used to define the distribution range of the two Fasciola sp ecies, regional variations in intensity and seasonal transmission patt erns at different sites. Results further indicate that many of the met hods used for crop productivity models can also be used to define the potential distribution and abundance of parasites. (C) 1998 Elsevier S cience B.V.