China has stepped up its battle against bird flu by introducing more rigorous monitoring and immunisation programmes.The ministry of agriculture has revealed that more than 91,000 birds have beenculled following a new outbreak. On Wednesday China said 2,600 birds died from the disease in Mongolia. The latest outbreak had been detected at a small farm with fewer than 10,000 birds, mainly chickens, geese and peacocks. In Thailand, meanwhile, a villager has become the 13th person in the country to die from bird flu, but the first this year. The victim’s son is being treated for flu-like symptoms. It is thought the pair contracted the virus from a bird and not from each other. Bird flu has killed at least 60 people in Asia since December 2003. Authorities say more wild birds appear to be dying from avian flu, an indication that the virus is changing. Experts have warned that countries around the world must be on guard against more virulent strains of H5N1.