NEW YORK-A virus from Africa strikes humans and birds in New York. A microbe common in the Caribbean causes dengue fever in the U.S. And that well-known tropical paradise, Minnesota, reports an increasing number of malaria cases. More than ever, public health experts say, the increase in international trade and travel is giving germs far easier means to hop halfway around the world, hitching rides in unsuspecting travelers. These travelers may not get sick until after they have returned home and exposed others to a disease that local doctors have difficulty diagnosing because they've never seen it before.

"In terms of microbes, borders are irrelevant, but they're more irrelevant than ever," said Dr. Steve Ostroff, acting deputy director of the Centers for Disease Control and Prevention. "Things and people move from one country to another with a speed and frequency never before seen, and that's a trend that is just going to continue" (Chicago Tribune,by Stevenson Swanson, October 7, 1999).