Category: Bird Flu

Reuters this week reported that poultry farmers should make sure to prevent sparrows, starlings, and pigeons from entering chicken houses because they could potentially infect poultry with the H5N1 bird flu virus.

I suppose that does make sense, but sounds rather impractical. Small birds have an amazing ability to worm (is that a suitable word?) their way into even the smallest of openings. Chimneys and vents are absolutely no problem for sparrows. It’s only a couple of months ago that I had to dismantle our heating system to release a trapped bird from the flu and there’s a tiny gap (half an inch?) between two roof tiles on our neighbour’s property into which starlings wantonly fly in and out on a daily basis.

Now, picture a chicken farm – I assume they’re referring to battery chickens rather than free range. Every chicken farm I’ve ever seen, and there are quite a few in this locale, has dodgy roof tiles, vents, ducts, openings, doors, even. And, dozens upon dozens of chickens feeding on all kinds of tasty grains and pellets. The temptation for any small bird is just too much and they flock in and out as often as they can get away with.

Admittedly, the article is referring mainly to small chicken coops, that are perhaps a little more manageable. But, that said, a poverty stricken keeper of a few domestic chickens may not have the means to repair one of those dodgy roofs even if it is small.

Regardless of what we do to protect poultry from H5N1 it is not likely that this viral strain specifically will be the culprit when a global pandemic gets underway. There are other strains, there are other viruses, the strain that will be P2P transmissable may already have jumped to another host, such as a pig on a Vietnamese smallholding or a cat in a Hong Kong market cage. It may even have made the leap to humans, in which case it is only a matter of time before it emerges into the wild.

No amount of fixing up chicken coops and keeping the starlings at bay is going to prevent that from happening.

Although H5N1, the avian influenza virus, darling of a scare-mongering media is lethal. No doubt about it. It’s just that at this point in human history, this virus is not in a human transmissable form, thankfully.

Now, a new study of patients who became infected with H5N1 in Vietnam has revealed clues as to why the virus is so lethal.

Menno de Jong and colleagues compared viral levels and effects on the immune system in one group of patients infected with H5N1 and another group infected with two types of human flu virus. The patients with H5N1 infection had much greater viral load in the throat than the patients infected with the human virus; markers of viral load were highest in the H5N1 patients who died. Virus could also frequently be detected in the blood of H5N1 patients but only in those who died.

The authors found that H5N1 virus at high levels triggers the release of inflammatory cytokines and that levels of these compounds is associated with a higher viral load. Fatal H5N1 infection was also associated with a loss of white blood cells in the peripheral blood.

The authors posit that H5N1 replicates much faster than human flu virus and that the high levels of the virus trigger an overwhelming inflammatory response that contributes to lung dysfunction and eventually death. They report their results in Nature Medicine today.

An important point that should be made is that the lower virulence of human flu is the mechanism by which this virus has remained endemic in humans and infects millions year in year out. If it were highly virulent, like H5N1, it would kill too many hosts to be persistent year in year out. As a dead host cannot infect another in the same way as a living one in direct contact. It is not necessarily true that H5N1 will mutate immediately into such a persistent viral sub-strain. The likelihood is that it will mutate into a fast-infecting form initially, but such a form will remove hosts from the ecosystem too quickly to remain endemic in the way that common human flu is. Viz, we don’t see the 1918 flu today because it died out.