Aug 29, 2011 (CIDRAP News) – The United Nations Food and Agriculture Organization (FAO) expressed renewed concern today about H5N1 avian influenza, warning of a "possible major resurgence" of bird outbreaks and saying that a vaccine-evading strain has emerged in Vietnam and China.
However, other influenza experts said the FAO statement was not surprising and did not offer new information that would suggest a significant increase in the threat posed by the virus, which has killed poultry in 63 countries since 2003 and caused 565 confirmed human illnesses with 331 deaths in that time.
After peaking in 2006, H5N1 outbreaks declined until mid 2008, but since then they have been increasing in number and expanding geographically, probably with help from migratory birds, the FAO said.
The number of outbreaks reached about 4,000 in 2006 before dropping off, the FAO said. It said about 302 outbreaks were reported in the first half of 2008. "But outbreaks have risen progressively since, with almost 800 cases recorded in 2010-2011," the statement said.
Also, 2008 marked the start of renewed geographic expansion of H5N1 in both poultry and wild birds, the agency said. In the past 2 years it has shown up in poultry or wild birds in countries that had been free of it for several years, including Israel and the Palestinian Territories, Bulgaria, Romania, Nepal, and Mongolia.
The long-distance movements of the virus seem to be associated with migratory birds, said FAO Chief Veterinary Officer Juan Lubroth. "Wild birds may introduce the virus, but people's actions in poultry production and marketing spread it," he said in the press release.
The agency also said a new H5N1 variant in Vietnam and China, called clade 126.96.36.199, is able to sidestep existing poultry vaccines. The strain has invaded most of northern and central Vietnam, and the country suspended its spring vaccination campaign this year as a result, the FAO said.
"Viet Nam's veterinary services are on high alert and reportedly considering a novel, targeted vaccination campaign this fall," the FAO stated. "Virus circulation in Viet Nam poses a direct threat to Cambodia, Thailand and Malaysia as well as endangering the Korean peninsula and Japan further afield. Wild bird migration can also spread the virus to other continents."
Lubroth said the recent increase in outbreaks could mean there will be a "flare-up" of H5N1 this fall in winter, with the virus popping up in unexpected places. The countries where the virus is endemic—Bangladesh, China, Egypt, India, Indonesia and Vietnam—are likely to face the biggest problems, but no country can consider itself safe, he said.
David A. Halvorson, DVM, an avian health expert at the University of Minnesota in St. Paul, said he didn't see anything surprising in the FAO statement.
"This appears to be a continuing situation where the Asian lineage HPAI [highly pathogenic avian influenza] H5N1 virus escapes from an endemic region and causes infection in another area," he commented. "That spread may come about by poultry movement or wild bird movement," he added, seconding Lubroth's comment on that point.
As for the new variant, he commented, "The appearance of mutant viruses that are able to bypass vaccinal immunity is not surprising; actually, with heavy vaccine use in the absence of other steps to completely control HPAI, the emergence of such viruses is to be expected."
Halvorson said it was reported earlier that Vietnam was suspending its vaccination campaign because officials didn't think it was working, which must have led to the identification of the new variant. "But everybody has said from the beginning that vaccination is not a primary [control] tool, it's secondary. And these countries that try to use it for a primary control method, it just won't work," he said.
He said his understanding is that Vietnam plans to make a new vaccine targeting the new variant.
Concerning the growing number of reported outbreaks, Halvorson cautioned that "incentives or disincentives" to report outbreaks can operate in any given country at any time, and therefore "it gets to where it's really difficult to know what's going on in any particular place."
Another expert, Michael T. Osterholm, PhD, MPH, voiced similar views about the FAO statement. He is director of the University of Minnesota's Center for Infectious Disease Research and Policy, which publishes CIDRAP News.
"I'm not sure what it means that the number of outbreaks is up this year. We don't know how good the surveillance is," he commented.
"We all know there's a risk of H5N1 changing and becoming much more lethal again in birds and humans. But there's no data that supports that's happening," Osterholm added.
Aug 29 FAO statement
Apr 13 CIDRAP News story "FAO: Eliminating H5N1 will take more than 10 years"
Sep 13, 2010, CIDRAP News story "FAO says H5N1 outbreaks are up this year"