The United Nations warned Monday of a possible resurgence of the bird flu virus, reports the Associated Press.

The Food and Agriculture Organization of the United Nations put out a statement urging the public to remain vigilant of a resurgence of the H5N1 Highly Pathogenic Avian Influenza as signs that a mutant strain of the virus is spreading in Asia. In a news statement, the organization notes that in China and Vietnam, a variant virus immune to current vaccines has been detected.

The advance in the virus seems to be linked with migratory bird movements, according to FAO Chief Veterinary Officer Juan Lubroth in the statement. Lubroth points out that the migrations allow the virus to travel over long distances and show up in new locations.

Wild birds may introduce the virus, but people's actions in poultry production and marketing spread it, Lubroth said.

According to WebMd, someone who catches the bird flu may experience typical flu-like symptoms at first, but then could develop severe respiratory problems which could ultimately be fatal. The site also said the virus could affect the digestive tract and the brain, but cautioned that symptoms of the virus change frequently.

The World Health Organization reported last week that a 6-year-old girl from Cambodia died Aug.14 from the bird flu, the eighth person in that country to die from the H5N1 virus this year, the Associated Press reports.

WHO has reported 331 deaths from 565 confirmed cases of the bird flu since 2003, the year the virus was first detected. During the first several years of the outbreak, FAO reports that 400 million domestic poultry was killed off because of the virus, which caused an estimated $20 billion of economic damage.

Recently affected countries include Israel, the Palestinian Territories, Bulgaria, Romania, Nepal and Mongolia, which have not seen cases of the virus in years. Countries where the virus is still firmly entrenched-notably Bangladesh, China, Egypt, India, Indonesia and Vietnam-are likely to face the strongest resurgence of the virus.