Map Credit FAO
After several days of anticipation – and a good deal of public speculation that Canada’s Fraser Valley bird flu outbreak might have been due to either H5N1 or H5N8 – it was revealed today that this outbreaks is the somewhat less alarming – but far from benign – H5N2 subtype.
The Canadian Press - ONLINE EDITION
By: The Canadian Press
Thursday, Dec. 4, 2014 at 12:58 PM
VANCOUVER - Tests results have confirmed the strain of avian influenza that has killed poultry on at least two farms in southwestern British Columbia is H5N2.
A turkey farm and a chicken farm located in the Fraser Valley were placed under quarantine earlier this week after the H5 virus was detected, but officials were still awaiting confirmation of the specific subtype.
As of this posting, there is no official statement on the CFIA (Canadian Food Inspection Agency) website, and a more complete analysis of the virus will probably take several days.
On Tuesday, in Fraser Valley B.C. Culling Poultry After Detecting H5 Avian Flu, I described 2 previous H5N2 outbreaks in the same region of Canada – one in 2005 and another in 2009. In 2010, we saw Low-path H5N2 confirmed in Manitoba. All three outbreaks were quickly contained.
H5N2 is generally found in wild birds, usually as an LPAI (Low pathogenic avian influenza) strain, but when it is introduced into large poultry populations it can evolve into a HPAI.
It was for this reason that OIE made both High and Low path H5 & H7 poultry outbreaks a reportable event back in 2004, and why quarantine and immediate culling are the preferred course of action whenever it either is detected. We’ve seen a number of HPAI and LPAI H5N2 outbreaks in the past, notably in Taiwan, China, Canada, the United States, Korea, Japan, and Mexico.
While not normally thought of as a serious threat to public health (see WHO: Human Risk From H5N2 Is Low), we have seen some limited evidence that H5N2 might be able to infect humans.
Nearly three years ago, in Taiwan: Three Poultry Workers Show H5N2 Antibodies, we looked at a report that three poultry workers and officials working in animal quarantine have tested positive for antibodies for the H5N2, but all remained healthy and asymptomatic (note: refer to article for other possible causes of seropositivity).
Some earlier H5N2 studies include:
J Epidemiol. 2008;18(4):160-6. Epub 2008 Jul 7.
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.
Serological survey of avian H5N2-subtype influenza virus infections in human populations.Yamazaki Y, Doy M, Okabe N, Yasui Y, Nakashima K, Fujieda T, Yamato S, Kawata Y, Ogata T.
While these reports are suggestive of prior H5N2 human infection – particularly among poultry workers – we haven’t seen any good evidence that it has produced significant or serious human illness.
However, in Human H5N2 bird flu infection: fact or fallacy? (May 2014) by Beuy Joob and Viroj Wiwanitkit, published in the Asian Pac J Trop Biomedicine, the authors argue:
. . . . the cross species infection from avian to mammal of H5N2 virus has already been confirmed in pigs and the possibility for further genetic reassortment to cause new H5N2 virus that might be highly virulent to human beings is also proposed. It is no doubt that the special concern and appropriate surveillance on the possible emerging human H5N2 bird flu is needed.
Which simply reminds us that influenza viruses are moving targets. What you can say about one today, may . . .or may not . . .hold true tomorrow.
As far as this current outbreaks is concerned – while there is no such thing as a `good’ H5 avian flu outbreak in poultry – if you were forced to choose between having an H5N1, H5N8, or an H5N2 outbreak . . . . I’m certain most poultry producers would choose H5N2.