CNN Health (Internet / TV) 02/20/06 http://edition.cnn.com/2006/HEALTH/conditions/02/19/birdflu.animals.ap/ One explanation may be the recent and wide-scale changes in how people interact with the environment in a more densely populated world that is growing warmer and in which travel is faster and move extensive, Marano said. Those changes can ensure that pathogens no longer stay restricted to animals, she added. Examples from recent human history include HIV, Marburg, SARS and other viruses. That prospect leaves open the question of what future threats await humans. "It always surprises us. We think that avian flu will be the next emerging disease. My guess is something else might come out before that," said Alan Barrett, of the University of Texas Medical Branch at Galveston. "It's very hard to anticipate what comes next." (This Associated Press article has appeared throughout the United States and abroad on TV and in Print.)