U.S. residents and tourists wait in line to cross to El Paso, Texas at the international border crossing bridge of Paso del Norte in Ciudad Juarez April 25, 2009. A new flu virus that has killed up to 81 people in Mexico could start a global epidemic, the World Health Organization warned on Saturday as the disease spread further in the United States. REUTERS/Alejandro Bringas (MEXICO DISASTER HEALTH)
REUTERS/STRINGER/MEXICO