As conferences covering both emerging infectious diseases and emerging zoonoses, influenza H5N1 was obviously a prominent topic of discussion. The big question wasn’t really answered–what is the most important mechanism of spread from country-to-country: wild birds, or domestic poultry? The only thing that was clear is that the answer, well, isn’t. I know grrlscientist has written extensively about the evidence against wild birds as a vector (using search word “influenza” here brings up many of them; more on her old site), and there certainly was a lot of discussion about farming and cultural practices that affect the emergence of avian influenza. More about this below.

A number of factors have been implicated in the emergence of this virus. One, the increase in poultry production in Asia without a concurrent increase in biosecurity. Two, changes in the virus itself. Three, human behavior and cultural practices, including weak veterinary services and a lack of transparency in diagnosis. Four, the question of wild birds and what role they may play. This is the first time since we’ve been observing avian influenza that a high-pathogenicity virus has been found in wild birds: did it arise there? Was it transferred there from domestic poultry? Is it being frequently re-introduced into the wild bird population, or are they spreading it amongst themselves without the aid of domestic birds? No one could answer these questions convincingly, and the answers have immediate real-life implications.

There are a number of factors that are being investigated in these areas. For example, in some high-risk areas in Vietnam free-range domestic ducks are raised that have contact with both wild birds and other domestic poultry–potentially a good way to spread H5N1 from wild birds to domestic ones, or vice-versa.

There is no question that most of the human cases thus far have had contact with domestic poultry. In many areas throughout Asia, such poultry mixes freely with humans and other domestic animals, and also has contact with a variety of wild animals as well. Live bird markets can further serve to disseminate virus as different species and animals from different areas mix. Slaughtering practices can also be very risky–for example, the practice of eating coagulated blood in “blood pudding” (not limited to using pig’s blood, as mentioned in the link). Fighting cocks have also been mentioned as a cultural risk factor for both spread among birds and potentially spread to humans. These birds travel, and are in close contact with not only other birds, but with their owners as well. The article mentions, for example:

…the owners scrubbed the blood off their birds with bare hands, wringing out the rags on the ground. Then, with ordinary thread, they stitched the wounds around their eyes and fed them painkillers. Sometimes, Phapart recounted as he watched the hurried surgery, the injuries are so severe that owners relieve the swelling by sucking out the blood by mouth.

The danger of many such practices can be minimized, however, with education and intervention. For example, the Tet festival in Vietnam in January-February, where there are large gatherings and an increase in the marketing of animals. In 2004 and 2005, H5N1 infections increased during this festival. In August 2005, vaccination in birds and a mass education campaign started, leading to a decreased prevalence of H5N1 infection in birds and subsequently fewer human cases during the festival. It’s difficult to ascribe a certain cause-effect relationship here, however, because there was no control group–infections could have decreased for reasons other than vaccination and education.

Some of the key issues and challenges, additionally, remain. Humans are still a “dead-end” host: we’re not good for further transmission of the virus. How long will this continue? In the interim, the virus is continuing to spread into humans, and we still need effective risk reduction measures. These include not only vaccination, but also increased biosecurity (since the virus is not yet efficiently airborne, cracking down on containment could prevent a good deal of spread), hygiene, education to modify practices and behaviors, increased veterinary services and understanding of the epidemiology of the virus (including the whole wild vs. domestic bird question). We also need good indicators to monitor and assess the effect of these changes, so we can know what’s actually working.

This isn’t easy. In many cases, the challenge is even greater, and we need a strong political commitment in addition to assistance by the general public. (For an example, look what’s happening in Indonesia and the political games being played). We also need the cooperation of people in many disciplines: not only those who deal with human health, but also those who deal with animal health, and agriculture, and wildlife, as a start.

We also need better ways to communicate to the public–more on this in a later post.

Image from http://www.sitting-ducks.com/ducks/sitduck.jpg

Comments

  1. #1 Greg
    April 4, 2006

    I’ve found your writings to be very interesting. I’m sure as the influenza H5N1 spreads; there will be a need for informative sites like this and others. We’re currently discussing in our forum, the fact that most humans cases of H5N1 were spread via human contact, either children playing with dead poultry or adults not protecting themselves while handling poultry.

    Keep up the good work.