Dear Martin/Devlin/Richard,

Cases of human infection that occurred in villages in China, Thailand, Turkey and Viet Nam before poultry cases were reported, but detected retrospectively, provide the visible evidence of non-reporting in the smallholder/backyard sector. Humans should not be the sentinels for infection in poultry but, repeatedly, this has been the case.

In the Turkish case there was a report in a US newspaper (NYTimes?) of trucks arriving in the town where the children died, carrying old broilers from a nearby factory that were sold off cheap. Not proof of anything, but a plausible way people could get infected ahead of backyard flocks.

In Viet Nam where I am working at present (incidentally, working on ways to protect the livelihood of the millions of households involved in rearing scavenging poultry) the Department of Livestock Production estimates that about 20% of the total chicken population(close to 40 million poultry) is in semi-intensive commercial flocks containing between 100 and 300 poultry. These are not part of integrated operations and are the flocks most at risk from H5N1 avian influenza because of their system of production and method of marketing. Ways need to be found to protect these poultry and some basic biosecurity (and vaccination) help to do so. These are the farms I was referring to in my posting and not the flocks owned by contractors working for integrated companies, which are usually larger and practice reasonable biosecurity.

I’m sure Devlin can help here: my understanding was [some at least] contract farms use chicks supplied by the big factory farms?

Anyone reading the Grain article would be led to your conclusion that The deadly H5N1 strain of bird flu is essentially a problem of industrial poultry practices. Its epicentre is the factory farms of China and Southeast Asia . However this statement is not consistent with the way H5N1 viruses emerged in Asia (through geese and live bird markets),

See below re Lhasa. Is that market a "wet" one?

with the lack of solid data on the exact mode of spread across Eurasia,

But there’s a perfectly rational and obvious explanation: the pattern of spread goes from east to west following road and railway lines. Avian flus have been moved along railway lines before: 1925 in the USA for example. Dirty carrying crates were apparently the vector then. The spread across Eurasia doesn’t follow any bird migration pathway, nor is there any species that begins its migration in the east in spring and ends up in the west in autumn. Migration is a forward-backward movement: if the disease went north in spring, it would come back south in autumn.

with the key role of free ranging domestic ducks in the maintenance and spread of H5N1 viruses since about year 2000,

But it’s very strange the disease hasn’t crossed from domestic free-range ducks to wild, migrant ducks (e.g. complete absence of the virus in healthy wild birds for the last decade at Mai Po). Shouldn’t wild bird populations be awash with the disease in Asia by now?

and the occurrence of cases since late 2004 in Asia which predominantly (but not exclusively) involved smallholder flocks (e.g. cases in Siberia in 2005, cases in Thailand in the second half of 2004 – see page 8 of AVIbull029a.pdf).

Again, there’s a perfectly rational explanation for this. One of the FAO bulletins reported that an outbreak in Lhasa, Tibet, in 2004 was traced back to Lanzhou, China, 1,500 km away. The outbreak was at the main poultry market in Lhasa. Suppose the birds had been sold to smallholders a day or two earlier at the market? Result: sudden, near simultaneous outbreaks in backyard farms across Tibet – precisely the pattern reported in e.g. the Ukraine. And where was the finger of blame pointed? Wild birds of course. And where is Lanzhou? A "hub" on the silk road, on a major railway line that runs from China to Eastern Europe.

Have large poultry farms contributed to the spread of H5N1? Absolutely and they have not helped their cause by covering up some outbreaks, but they are not alone in doing so.

I’m sure, therefore, you can understand our frustration when the popular belief is that wild birds are the sole spreaders of the virus. Sure they could be playing a part, but a very minor one at most.

Finally, for your information, I had read the whole report on the day the news article was released. Unfounded comments to suggest otherwise are not particularly helpful in a forum such as this.