A German Teal and some epidemiological hand waiving

A teal - stunning little bird. But also at present in the center of H5N8 flu business. (Picture from http://www.rspb.org.uk/).

A teal – what a stunning little bird! But also at present in the center of H5N8 flu business. (Picture from http://www.rspb.org.uk/).

By Jonas Waldenström

As most of you know by now, we have a new highly pathogenic avian flu virus in our midst. This virus, of the H5N8 subtype, has been detected in Germany, the Netherlands and the UK in the last two weeks.

The epidemiology of highly pathogenic viruses is quite different from that of their low pathogenic cousins. While low pathogenic viruses are essentially waterfowl viruses, and generally benign, highly pathogenic viruses tend to mainly go rampage in domestic poultry, and are not disseminated broadly in wild bird populations. One important exception is/was the H5N1 virus, that apart from affecting the poultry industry also caused several outbreaks among wild birds in Europe in 2005-2006, but with varying pathogenicity in different avian species.

The new H5N8 virus entered the European scene quite unexpectedly. The closest described outbreak before Germany was Southeast Asia, where this virus had been detected in poultry (and some wild birds) in Korea, China and Japan. That’s quite a leap for a microbe, nearly halfway around the globe.

Phylogenetic studies have confirmed that the current outbreak strain is genetically highly similar to the virus from Asia. Thus the question is really: how the heck did it get here? Officials from OIE and others were quick to point the gun at wild birds. But regardless of how well we know that waterfowl can be hosts of low pathogenic viruses, and that some species can harbor highly pathogenic viruses asymptomatically, there are no direct migration routes in autumn between the two areas. Thus, if the virus entered Europe via wild waterfowl it must either been around in wild bird populations for a longer time, allowing sequential transmission between different populations/species at shared breeding or stopover sites, or there might have been undetected outbreaks in poultry further west (e.g. Russia) where virus has disseminated into wild bird populations migrating westward. Neither do we know how this particular virus affects wild birds – is pathogenic to waterfowl, does it interfere with migration, how long do infected birds shed virus, etc?

An alternative hypothesis, of course, is that it has reached Europe as part of the trade with poultry and products. After all, the chicken is the most common migratory bird on the planet, although it doesn’t fly on its own wings.

The ‘chicken vs. duck’ argument is an inflamed old discussion, where different people tend to have polarized positions. In my opinion, a middle stance is more appropriate. Likely, both wild birds and poultry can affect geographic spread of highly pathogenic viruses, but the circumstances may act differently from case to case.

The biggest problem at present is our lack of data. A few days ago, the H5N8 virus was identified in a Teal shot as part of active surveillance in Germany. Depending on your preferences, this finding in a healthy duck (that’s at least what the reports say) could either be a ‘game changer’, providing evidence for a link to wild birds, or a spillover event from poultry to wild birds.

Instead of arguing based on a single Teal, we need to gather much more data. And do so quickly. We should ramp up active surveillance in both poultry and wild birds. During the H5N1 years, a network of ornithologists and virologists was created that substantially contributed to the increased knowledge base on influenza A virus epidemiology and ecology. This network was mostly dismantled when the H5N1 virus disappeared from the European scene, but the core is still there and would be easy to gear up again.

Let’s do that, shall we?


As pointed out to me on Twitter and here on the blog, there are indeed more wild bird sequences of H5N8 that are interesting (see here for instance) in this context. This is an interesting virus, and more info is likely to follow. Near identical sequences in wild ducks in Chiba, Japan, to the viruses detected at same time in Germany is indeed a strong argument for wild bird involvement in geographical spread.

However, my main points – that our different preconceptions tend to make the discussion too black and white, and that we need to obtain more data – are still very much valid.


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2 thoughts on “A German Teal and some epidemiological hand waiving

  1. they breed in Sibera and migrate to Europe and Korea in fall.
    This is consistent with the sequences that suggest a common ancestor
    for the Dutch and English (and Japanese Nov.2014) H5N8 as of ~July 2014
    and a common ancestor as of ~Oct.2013 for the European and Jan.2014
    Korean sequences
    of the

    • Yes, waterfowl with different wintering areas (Europe and Asia) meet during breeding times and early parts of migration (as for instance Siberia). That is what I would refer to as indirect links, mediated by sequential passage between populations/species. There are no waterfowl that fly directly from southeast Asia to winter in Western Europe, or vice versa.

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