#4000
imported_Martin
Participant

a response to above email, from Nial Moores of Birds Korea:

Read your mail below with interest, especially the part,

Quote:
this indicates that the virus had been brought there, most likely (in the absecne of poultry infections) through leap-frog infections of birds that died after passing the infection to others

Writing as a non-expert in disease, but as one who is really trying to understand the nature of H5N1, I would genuinely appreciate further advice and insight.

From what I understand, based on what we can be pieced together in East Asia, there has been no evidence at all for leap-frog infections between wild birds in this region.

Wild birds have come into contact with the virus: if they were infected, they died (in >99 % of known cases; and even in the v. significantly less than 1% remainder, we perhaps dont know whether death would have followed over time). In many cases (Qinghai, Mongolian lakes, Hong Kong), even birds sharing the same wetland with infected individuals did not become infected.

In the absence of an alternative hypothesis, is it not reasonable to assume that high path H5N1 (in East Asia at least) is very virulent, but that it is actually quite poor in terms of transmissibility? Is this not why it requires the dense concentrations of other birds in artificially maintained conditions to stay virulent and to transmit easily?

There have been, in over 9 years, no obvious or proven leap-frog infections between wild birds in Hong Kong, Japan, Korea, Mongolia and China, as far as can be made out.

Instead, it appeears wild birds were infected by more or less direct contact with infected poultry, poultry products/environmental contamination, caged birds, and in a few cases, where surely no other reasonable hypothesis exits, by scavenging on waste/dead birds (e.g. Magpie in Korea, Large-billed Crows in Japan). In all cases, the vast majority of wild birds remained uninfected. Consider those Magpies and Large-billed Crows (species that very often form large roosts in Korea and Japan): no large roosts were affected, and concentrated testing of these species in those countries showed no evidence of H5N1 in any but the birds that died.

If there had been wild bird to wild bird transmission, it would seem very likely that we would have seen ripples of spread, simultaneous outbreaks, sudden die-offs in wild bird flocks, LOTS more birds testing H5N1 positive in these countries. We have not. Instead, we have seen wild birds infected, and local deaths over a rather short time-frame (in all cases until Mongolia fairly easily explained by the local influence of poultry and poultry products or of market birds; and even in that case a gap of only a few hundred km from the infected poultry of southern Siberia, within the flight range of one or more likely several sick infected duck it seems, this in itself relevant to the European cases perhaps?).

What we have been seeing in Europe does seem to be different, at least on the surface. No mass die offs (in western europe at least), but instead scattered cases of deaths in a few species, from Tufted Ducks, especially Mute Swans over several weeks to e.g. a presumably scavenging Buzzard.

Looking closer, though it starts to look less different – East Asia minus the big die-offs…a few birds here, there, and in the absence of the local reservoir of the disease, or of more birds coming from an infected area, the so-called outbreaks seem to trail off.

There are several things that strike me as potentially significant in the Euopean pattern so far..would others agree? (asked without irony and in the hope of hearing peoples thoughts):

1) We know that infections in poultry have become endemic/near-endemic in parts of Turkey and elsewhere in SE/E Europe/W. Asia, and that the virus has become widespread in poultry in parts of Russia (pres all linked by a transport system);
2) We know that there has been a repeated state of denial about such outbreaks, and that trade through the region and from the region is very complex;
3) We know/suspect that there have been/were repeated outbreaks in wild birds in some of the same areas (ie parts of SE/E Europe/W. Asia), some outbreaks claimed to be large, then denied etc;
4) We know that there has been very severe and prolonged cold weather to the east of western europe, affecting some of the same regions;
5) we can see that the majority of infected wild birds are/were being found towards the east of Europe – Sweden, Germany, Italy etc, with none so far (is this correct) in the far west (i.e. UK, Spain , Portugal): ie in areas closest geographically to regions where the disease is already in poultry;
6) We know that bird movements and migration is far more complex than most people are presenting, with lots of smaller movements taking place and species-specific routes within flyways, which themselves are very wide at points (narrower at others). These more local movements include some species of geese and swans in mid-winter, with birds move west to eg the Netherlands, and then on to the UK only when conditions demand it, with in some winters birds even proven to commute between the two, responding to food availability and their fitness;
7) We can suspect that while some species were moving west from frozen wetlands into western Europe until very recently, that now some other species are moving north (I can see on UK birding websites news of the first Barn Swallows and Wheatears arriving, late but now in), as temperatures start to rise.
8) After a week or two of dead wild bird discoveries and new countries infected in western europe, it seems, for now, like the pace has changed – and infections are now being found again more often closer to the regional reservoir (eg outbreaks in Israel, human death in Egypt, continuing a fairly consistent spread closer to the epicentre)?
9) We can now see, for now at least, that the dead wild birds in (northern) parts of Europe were the last link in the chain of infection. They failed to infect other wild birds leap-frog style, unless perhaps through other species scavenging on them also becoming infected (again suggesting high virulence, poor rates of transmission?)
10) Finally, we do not know, but we can suspect, that there are now several potential sources of infection either within or just outside western Europe which can complicate the pattern further.

For the virus to leap frog between wild bird species, as a way of explaining scattered dead wild birds in Europe, would this not mean that the virus would need to have acquired a new level of transmissibility (so that it retains its high path state after repeated transmission in wild birds)?

If this is so, and in the absence of such a pattern In Asia, would not something likely have needed to change in the virus itself within recent weeks (this is asked without irony – I would very much like to understand)? Is there evidence of this?

And if so, if the virus has changed in this way, why are people in western Europe only apparently still only seeing the end link in that chain? Why, when these Mute Swans and Tufted Ducks reach western Europe and die, are there not continuing rippling patterns of spread on neighboring ponds and waterways?

In the hope of enlightenment,

Respectfully,

Nial Moores
Birds Korea