By Maggie Fox, Health and Science Editor WASHINGTON, Dec 4 (Reuters) - Infected poultry imported by Brazil, Canada or Mexico is the most likely route for bird flu to spread into the Americas, a group of researchers predicted on Monday. Migrating fowl would then spread the H5N1 avian flu virus throughout the region, the U.S. and British researchers predicted. "We need to make sure that we are preparing developing countries in this hemisphere for this outbreak," said Peter Marra of the Smithsonian Institution and the National Zoo in Washington, who worked on the report. Their study of the movement of H5N1 out of China and into the rest of Asia, across Europe and into parts of the Middle East and Africa shows that the poultry trade often started a spread that wild birds then took further. "We conclude that the most effective strategy to prevent H5N1 from being introduced into the western hemisphere would be strict controls or a ban on the importation of poultry and wild birds into the Americas and stronger enforcement to curb illegal trade," they wrote in their report, published in the Proceedings of the National Academy of Sciences. Marra said Canada, Mexico and other countries all regularly import day-old chicks from other regions. The United States does not. The H5N1 avian flu virus has killed or caused the slaughter of more than 200 million birds globally since 2003. While it mainly infects birds now, experts say it could evolve into a pandemic strain that infects people easily, although up to now it has infected only 258 people and killed 154. Both poultry imports and migrating birds have been blamed for the virus' rapid spread. It has now been found in birds in 55 countries, and neither repeated slaughtering of flocks nor vaccination has been able to stop it completely. U.S. government teams are monitoring waterfowl flying into Alaska from Siberia and then south from Alaska, and they are also checking birds along the northern U.S. border for the virus. GENETIC CLUES Marra, Marm Kilpatrick of the Consortium for Conservation Medicine in New York and colleagues looked to see how and where H5N1 has spread in the past. This can be done by looking at the genetic sequence of the virus, which is constantly mutating, and at migratory patterns. While the virus mostly spread in Asia through the poultry trade, almost all of the spread throughout Europe was due to migratory birds and both poultry and wild birds carried it into and across Africa, they concluded. Some outbreaks are more difficult to explain. "H5N1 outbreaks in South Korea, Russia, Mongolia, Nigeria, India, Pakistan, and Cameroon were inconsistent with both reported poultry trade (no poultry imports were reported from H5N1-infected countries) and the timing and direction of migratory bird travel in the month of the outbreaks," the researchers wrote. Illegal trade in chicken feces for fertilizer and fish food, wild bird trade or other factors may have been responsible, they said. The genetic fingerprints of the viruses found in these countries gave little clue as to their origin, Marra said. They said their study showed it is unlikely bird flu will come into the United States and Canada via Siberia. Marra said the surveys of live birds in Alaska and on the west coast should continue. "Yet to not have some sort of systematic surveillance around the rest of the United States is, I think, a mistake," Marra said in a telephone interview.
