Whack-a-flu

By Jonas Waldenström

These are interesting times in avian flu research. International disease reporting fora are full of notifications on avian influenza viruses in different parts of the world – China, USA, Egypt, Israel, Korea, Taiwan, Bulgaria, Nigeria. It’s like the game of whack-a-mole, where two new viruses appear as soon as one virus disappears. The current list of viruses includes some that have been around for awhile, such as the highly pathogenic H5N1 virus that has been endemic in parts of Asia and Egypt the last ten years, causing outbreaks in poultry and a few, but severe cases in people. Another one is low pathogenic H7N9, which repeatedly is causing human infection in China, and where worries are that we will see more cases as winter progresses.

On top of these we have some new kids on the block. A particular interesting one is the highly pathogenic H5N8 virus, and related reassorted viruses. During 2014, this virus hit the poultry industry in Korea, and 14 million chickens were culled in order to get the epizootic in check. In the later part of the year, the geographical range of the virus expanded, with detection in both wild and domestic birds in China and Japan, and later, after a giant leap, in Germany, the Netherlands, UK, and Italy.

Over the holiday season, highly pathogenic H5N2, H5N1 and H5N8 viruses have popped up in North America. Among the birds infected we find several wild birds, either detected through passive surveillance of dead birds, or through active targeted surveillance. Interestingly, these viruses have gene segments from the highly pathogenic H5N8 virus that circulates in Eurasia, but have reassorted with avian influenza viruses native to North America.

There are a couple of things worth noticing here. To start with, this new group of H5 viruses has made a remarkable geographic range expansion in a considerable short time. There has been repeated detection in wild birds in areas where no poultry cases have been detected, suggesting an active role of wild birds in distance dispersal. Furthermore, although some birds have been found dead (mainly non-reservoir species for low pathogenic viruses) there have been cases of H5N8 (and related viruses) retrieved from healthy waterfowl, again suggesting that this particular hemagglutinin may have a high fitness among wild birds. Moreover, the fact that this virus has reassorted with North American avian lineages suggests that it may be able to persist in the virus population for some time ahead.

In light of all this it is really about time to ramp up avian flu surveillance in Europe too. We need to collect and analyze many more wild bird samples than what is currently done, and couple this data with targeted experimental studies.

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2 thoughts on “Whack-a-flu

  1. H5 went from Asia to America, but people don’t care a lot. How times changed.
    IMO you should have mentioned that Eurasian and American avian flu
    _rarely_ mixes

    • Yes, you are right. They do mix, but rather infrequent. Our group have stumbled on mixed North American/Eurasian AIVs over the years in seabirds and in samples from Alaska. And there is evidence from the US on how an Eurasian segment can increase in frequency in NA.

      Still, the main patterns across segments and subtypes are separation by continents, which is equal to a general obstacle for gene flow. Interesting how quick the H5N8 HPAI virus did the jump. I mean, the scientists in US searched high and low for H5N1 in Alaska for many years.

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