(CBS/AP) Is bird flu mounting a comeback? The United Nations has issued a warning, saying wild bird migrations have brought the deadly influenza virus back to previously virus-free countries and that a mutant strain of H5N1 was spreading in Asia.
The strain, which can apparently sidestep defenses of existing vaccines, is spreading in China and Vietnam, the U.N. Food and Agriculture Organization said in a statement on Monday. It urged greater surveillance to ensure that any outbreaks are contained.
Last week, the World Health Organization reported that a 6-year-old Cambodian girl died Aug. 14 from bird flu, the eighth person to die from H5N1 avian influenza this year in Cambodia.
Vietnam suspended its springtime poultry vaccination this year, the U.N. said. Most of the northern and central parts of the country - where the virus is endemic - have been invaded by the new strain.
Elsewhere, the U.N. says bird migrations over the past two years have brought H5N1 to countries that for years had been virus-free, including Israel, the Palestinian territories, Bulgaria, Romania, Nepal and Mongolia.
"Wild birds may introduce the virus, but people's actions in poultry production and marketing spread it," said the U.N. agency's chief veterinary officer, Juan Lubroth.
Globally, there have been 331 human deaths from 565 confirmed bird flu cases since 2003 when it was first detected, the WHO said.
The virus was eliminated from most of the 63 countries infected at its peak in 2006, but it remained endemic in Bangladesh, China, Egypt, India, Indonesia and Vietnam.
The number of outbreaks in poultry and wild bird populations shrank from a high of 4,000 to 302 in mid-2008, but outbreaks have risen progressively since, with almost 800 cases reported in 2010-2011, the U.N. said.
"The general departure from the progressive decline in 2004-2008 could mean that there will be a flare-up of H5N1 this fall and winter, with people unexpectedly finding the virus in their backyard," Lubroth said in a statement.
Avian influenza affects both wild and domestic birds, including ducks, gulls, chicken, and turkey. It can spread to people who have extensive contact with infected birds - but not by eating poultry or eggs that have been properly prepared.In humans, bird flu can cause problems ranging from eye infections to flu-like symptoms and severe respiratory problems.
The CDC has more on avian influenza.