Photo Credit – FAO
There are several variations of this news report floating across the wires this morning, but in the end, it may turn out that there is less to this story than at first appears.
The gist of the story is that three poultry workers and/or animal quarantine officers who worked at a farm where the H5N2 virus was recently discovered have tested positive for antibodies to the H5N2 virus.
H5N2, while an avian influenza virus, is currently considered a far less dangerous pathogen than its infamous cousin, H5N1.
But all H5 viruses (along with H7s) are reportable to the OIE because of their potential to evolve into more dangerous viruses, particularly when they are allowed to proliferate in large flocks of poultry.
First a link to the Taiwan story, then I’ll return with more:
Taipei, April 22 (CNA) The Centers for Disease Control (CDC) confirmed Sunday that three poultry workers and officials working in animal quarantine have tested positive for antibodies for the H5N2 strain of avian influenza.
However, all three people are healthy and none have developed any flu symptoms, CDC Deputy Director-General Chou Jih-haw said, adding that there is no public health risk of human-to-human transmission.
While antibodies to the H5N2 virus have been detected a few times in humans in the past, the virus has never been shown to cause illness in human hosts.
A couple of studies in the past include:
J Epidemiol. 2008;18(4):160-6. Epub 2008 Jul 7.
Human H5N2 avian influenza infection in Japan and the factors associated with high H5N2-neutralizing antibody titer.
Ogata T, Yamazaki Y, Okabe N, Nakamura Y, Tashiro M, Nagata N, Itamura S, Yasui Y, Nakashima K, Doi M, Izumi Y, Fujieda T, Yamato S, Kawada Y.
Arch Virol. 2009;154(3):421-7. Epub 2009 Feb 3.
Yamazaki Y, Doy M, Okabe N, Yasui Y, Nakashima K, Fujieda T, Yamato S, Kawata Y, Ogata T.
While suggestive of prior H5N2 infection, there is precious little evidence to link any significant or serious human illness to the H5N2 virus.
Complicating the story out of Taiwan is the fact that, starting in 2010, Taiwan began offering soon-to-expire H5N1 vaccine to high risk members of their population, including poultry workers and animal quarantine officers.
See Focus Taiwan article from Sept 1st, 2010 titled CDC begins national bird flu vaccination program for details.
So while it is possible that these three workers acquired H5N2 antibodies from direct exposure to infected poultry, it may simply be that their tests are showing cross-reactivity to H5N1 antibodies created by the bird flu vaccine they received.
It has also been suggested that a history of seasonal influenza vaccinations could produce H5N2-neutralizing antibody positivity as well.
Which leaves us with an intriguing story, but one with a lot of possible holes in it.
For more on the H5N2 virus in Taiwan, you may wish to revisit: