The United Nations agricultural agency on Monday issues a new warning that bird flu viruses are on the rise again in China and urged neighboring countries to be extra vigilant.“FAO (Food and Agricultural Organization) called upon neighboring countries to remain vigilant in the face of H7N9 and other avian influenza viruses, such as highly pathogenic avian influenza H5N1,” the U.N. agency said in a news release.The number of human infection of H7N9 has considerably increased since late December in East and Southeast China, the U.N. World Health Organization (WHO) has said. At least seven cases of H7N9 infections have been reported this year, according to local reports.WHO Director-General Margaret Chan stressed that “vigilance is our watchword,” in remarks addressing WHO Executive Board in Geneva.“Chinese authorities are enforcing important measures to reduce the risk of human exposure to the A(H7N9) virus,” said FAO Chief Veterinary Officer Juan Lubroth. “But countries need to stay alert, as the virus continues to circulate in poultry without showing any visible clinical signs.”