Monday, February 07, 2005

Bird flu and bird farms, part III

This is a second installment in anthropologist Ronald Nigh's perspective on the bird flu problem in southeast asia (previous posts here and here). It is written specially for Effect Measure, for which we are grateful. We present it here as a contribution to a debate that should happen (but to date hasn't). The first two paragraphs are a bridge from the last post.
The story I have been putting together is quite different. It is a complex story, with many pieces still missing. The picture that is emerging, though, is that the rapid development of the confined poultry industry and associated technological changes and export trade has resulted in the appearance and rapid propagation of new, highly virulent strains of poultry diseases, some of which affect humans. These new strains not only represent a major threat to the future of poultry production but have resulted in serious potential threats to human health with very high costs for society. The solution to this problem is not more of the same, i.e. more high tech solutions, drugs, "biosecurity " and " best practices " applied to confined poultry operations, but rather to reverse the trend, back up from this dead end, abandon large chicken confinements and return to decentralized production in small flocks widely distributed in the countryside. This also implies that long-distance, " global " trade in poultry products would be largely abandoned.

Such conclusions may seem absurd at first, but if we look at the reality of our situation, they become inevitable.

We can illustrate the points by looking at the development of one key disease organism, Infectious Bursal Disease Virus, IBDV. Known since at least the 1950s, IBD has long been considered a mild infection, since in its classic form it causes reduced growth and other problems it is less fatal than other "catastrophic " plagues such as avian flu or velogenic Newcastle. New strains have arisen since the rapid growth of chicken confinements, however. IBDV is drawing attention today, as it is thought to be an important factor in creating the conditions for the current H5N1 epidemic.

IBD causes immunosuppressive disease in young chickens. Thus, its most important effect is secondary, reducing the effectiveness of vaccines and of the bird‚s natural immune response to other, often fatal, diseases. This site gives a background on IBD and how it has mutated:

"IBD or Gumboro is an old disease and has been described by scientists all over the world. It is caused by a birnavirus, which targets the bursa of Fabricius --the primary organ involved in the development of the chicken's immune system. Most of the economic devastation associated with IBD is due to its immunosuppressive effects that lead to poor vaccination response, secondary bacterial, viral and protozoan infections and poor performance. The virus is now recognized in every poultry-producing country in the world. First diagnosed in 1962, the virus has since then changed and manifested itself in different forms that made it even a bigger threat to the industry."

The authors talk about the " classic form ", known scientifically since 1962 with a series of noticeable symptoms. Then around 1980 (large chicken confinements started to take off in the US in the early 1970s) variant strains began to appear, such as the Delaware strain and others. With these variant viruses, the usual symptoms of IBD are often not observed, but infection is quickly followed by others, especially, respiratory diseases.

What are the causes of the emergence of this new strain of IBDV? The authors list them:
  • Extreme vaccination pressure
1. Use of cloned intermediate IBD vaccine that confers very narrow protection.
2. Vaccinating breeders with inactivated classic-type virus only resulting in chick hatching with maternal antibodies of limited to the classic type.
  • Short down time between grow-out.
  • Improper cleaning and disinfection. Some growers "dry-clean" only by removing manure and blowing down dust.
  • Increased bird population.
They note that during epidemics, the farms implement biosecurity measures, but over time, these are inevitably abandoned in an effort to cut costs.
Final installment to come.