Galveston County Daily News (Internet / Print) 03/31/06 Environmental change and viral mutations have combined to fuel outbreaks of a deadly mosquito-borne disease that have plagued South and Central America for the last 100 years, a new study by University of Texas Medical Branch at Galveston and Colorado State University researchers reports. The scientists discovered that a single common genetic mutation can turn a harmless virus circulating among rodents in New World tropical forests into a strain of deadly Venezuelan equine encephalitis virus that strikes humans, horses, donkeys and mules. “The critical thing is really the presence of vulnerable equine species on these ranches in areas that used to be forests,” said UTMB pathology professor Scott Weaver, senior author of a paper on the study appearing in the Tuesday issue of the Proceedings of the National Academy of Sciences and now available online at the PNAS Web site.