Apr 13, 2011 (CIDRAP News) – Because of deep-rooted barriers, there is little chance that H5N1 avian influenza can be expelled within the next 10 years from the six countries where it remains entrenched, the United Nations Food and Agriculture Organization (FAO) says in a new report.
Most of the 60-plus countries that reported H5N1 in 2006 have eliminated it since then, but it remains endemic in China, Vietnam, Indonesia, Bangladesh, India, and Egypt, notes the report, titled "Approaches to Controlling, Preventing and Eliminating H5N1 Highly Pathogenic Avian Influenza in Endemic Countries."
The FAO says the elimination effort faces three major obstacles in these countries: the structure of the poultry industry, the quality of veterinary and animal production services, and the level of commitment by all sectors.
"Although measures have been introduced in all endemically infected countries to address these three factors, all require further long-term commitments and investment if the virus is to be eliminated," the report states. "It is now generally accepted that the H5N1 HPAI [highly pathogenic avian influenza] virus is unlikely to be eliminated from poultry in these countries and regions for the next ten years at least."
Further, the report says "there is no guarantee that the current incremental approach will eliminate H5N1 HPAI." The goal may require innovative measures such as new, easily deliverable poultry vaccines and genetic manipulation of poultry to make them resistant to the virus.
As long as H5N1 outbreaks continue, so will the risk of the virus evolving into a human pandemic strain, the report notes. Several of the H5N1-endemic countries have had human H5N1 cases this year, with Egypt leading the list with 22 confirmed cases so far.
The nature of the poultry business in the countries still plagued by H5N1 makes elimination difficult, the FAO report says. Production and market chains are "complex and poorly integrated," a large share of poultry are reared and sold in conditions that offer little protection against avian flu, many poultry (such as domestic ducks) don't show signs of the disease when infected, and supporting entities such as producer associations are weak.
Changes are being made in the poultry sector, but they won't eliminate all high-risk practices, such as free-grazing ducks, the report adds.
A second difficulty is that veterinary and animal production services in the affected countries have limited capacity to identify and respond to cases and make needed changes in production and marketing systems, the FAO says. It asserts that "disease investigations and tracing rarely identify the source(s) of the outbreak."
Part of the problem is that there are limited links between the public and private sectors, the agency says, adding, "Disease reporting systems rely on reports of disease from producers, many of whom are wary after unhappy past experiences with government veterinary services, especially those that carried out mass culling or offered poor compensation for poultry destroyed."
The third barrier to elimination of H5N1 is a lack of commitment within the poultry sector, governments, and the public, according to the report. Support for the type of measures needed to eliminate the disease from zones or whole countries "will be half-hearted until most farmers regard H5N1 HPAI as a serious threat to their livelihoods and well-being."
Lessons of the past 5 years
The report presents a variety of lessons learned about H5N1 over the past 5 years, on topics such as the value of vaccination and the role of wild birds.
One is that even in "endemically infected countries," well-managed farms can keep the virus out by using stringent biosecurity measures and, in some cases, vaccination. That has been demonstrated in Shandong province in China.
The FAO says the areas that have succeeded the best in controlling H5N1 are those that have "intensive" poultry production methods with tight biosecurity measures and controls on the movement of poultry.
But the report goes on to say, "FAO does not recommend that all poultry be reared under industrialized conditions. It does recommend the use of appropriate, affordable and well-designed management biosecurity systems for commercial farms, markets, and places where traditional village-based flocks are reared."
On the role of wild birds in spreading the virus, the report says the movement of poultry should generally be considered the source of new outbreaks in H5N1-endemic countries, but wild birds have introduced the virus in some places. It is now "generally accepted" that wild birds helped transfer clade 2.2 viruses from Asia to Europe and Africa in 2005 and 2006, it states.
In that vein, the FAO says it is "encouraging" that clade 2.2 viruses seem to have disappeared from migratory bird populations, as no new cases linked to that strain have been seen in Europe in the past year. In contrast to the experience with clade 2.2 viruses in 2005-06, clade 2.3.2 viruses have not caused major poultry losses in Europe or in Asia outside the endemically infected countries.
Concerning vaccination, the FAO says it has its uses and its dangers. When used properly, it makes birds more resistant to the virus and it reduces virus shedding if they get infected despite vaccination.
Mass vaccination campaigns are expensive and difficult, the FAO says. As carried out in China and Vietnam, such efforts will never make it possible to stop all transmission, but they do protect individual flocks and reduce the number of fully susceptible poultry. On the other hand, emergency vaccination in response to an outbreak creates a major risk of spreading the virus, and vaccination complicates serologic testing to detect infection in poultry.
The report offers a fairly long list of non-technical measures to help control H5N1, including things like increased compensation to farmers for destroyed flocks and greater engagement with both small- and large-scale poultry farmers. It concludes with a list of innovative technical methods that might be tried, including:
- Vaccines that don't require individual injection of each bird and provide long-term immunity
- Development of genetically resistant poultry
- Methods for temporarily increasing the resistance of poultry, such as administering short interfering RNA before selling birds at live markets
- "Universal" human vaccines for influenza A
- Reconsidering the pros and cons of novel vaccines, such as live-virus vaccines, which are not currently recommend for poultry
FAO H5N1 report