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Influenza Aviar: Una crisis global de sanidad animal con profundos desafíos a la ciencia y la sociedad

Samuel C. Jutzi, Director, Animal Production and Health Division
Joseph Domenech, Head, Animal Health Service and Chief Veterinary Officer
FAO, Rome, Italy
August 2006

The Disease - A Global Challenge to Agriculture and Public Health

The first Asian H5N1 highly pathogenic avian influenza (HPAI) strain emerged in 1996 when it was identified in geese in Guangdong Province in southern China. It then caused disease in Hong Kong SAR where poultry and humans were affected in 1997, poultry only in 2001 and early 2002 and poultry and captive wild birds in 2002/3. By this time, infection with a range of H5N1 HPAI virus genotypes was present in an arc extending from Hanoi to Shanghai, yet apart from Hong Kong, no disease was reported. From 2003 onwards the disease spread widely, initially through East and Southeast Asia in 2003/4 and then into Mongolia, southern Russia, the Middle East and to Europe, Africa and South Asia in 2005/6. Migratory birds appear to have played a role in some of these movements.

During this time H5N1 HPAI has attracted very considerable public and media attention because the viruses involved produced fatal zoonotic disease in a small number of humans exposed to the viruses and because of the potential to acquire the capacity to be transmitted from humans to humans, a prerequisite for a human pandemic strain. Although the possibility exists that avian influenza caused by H5N1 viruses leads to a global influenza pandemic, H5N1 has not yet been found to be easily transmissible from birds to humans and even less, if at all, among humans.

The Impact of the Disease and of its Control

With the fear of the spread of avian influenza, many decision makers are asking how to best prevent the introduction of HPAI to their country or if it is already in their country how to prevent further spread and having it become endemic. Emergency control measures to eliminate new outbreaks of HPAI and to stop the spread of the disease have centred on stamping out which may entail the large scale culling of infected flocks and contact flocks. The high concentration of poultry in certain areas has led to the culling of millions of animals at great expense. For low income countries in which poultry is raised primarily by smallholders who can generate important income from raising birds, such measures may seriously threaten smallholder poultry operations.

For those countries with a large number of backyard producers, poultry production is an important contributor to the livelihood of many poor households. Further, poultry meat and eggs are important sources of essential micronutrients for the poor, children and women, and it is known that in general small animal husbandry is positively associated with intake of animal source foods. The economic and nutritional losses faced by poor producers in these countries, depending on the strategy chosen to control HPAI, could be devastating, as would be the accelerated loss of animal genetic diversity.

Though the viruses have had a significant impact on producers, and in particular on backyard producers, the direct cost of the disease has been dwarfed by the devastating impact on poultry producers globally caused by market shocks driven largely by misplaced public fears regarding safety of poultry products. These concerns, fuelled in part by the media, have led to a marked fall in sales and prices for poultry products.

Much is not Known of the Disease and its Origins

There is a range of unresolved questions regarding the emergence and spread of H5N1 HPAI since 1996. One school of thought suggests that rapidly expanding intensive or industrial farming has played a pivotal role whereas others see this largely as a disease of smallholder poultry, brought about by failure or inability to implement appropriate biosecurity/quality management systems as smallholder flocks expanded. FAO argues that both have played a role and any attempt to blame a particular practice or sector for emergence of this disease fails to recognise the complexity of the poultry industry and the pitfalls and benefits of the various management systems employed from a veterinary, social and economic perspective. The crucial role of ducks in open farming systems and of live bird markets as reservoirs of infection also needs to be recognised as well as ways by which these risks are managed or have failed to be managed.

Worldwide the Poultry Sector is Growing and Changing Rapidly

Rearing of poultry has long played and continues to play a crucial role in rural development due to the relatively low entry cost and the potentially high returns for smallholders who expand their flocks. Many smallholders have responded to increased market demands created by large urban centres by rearing additional poultry but are now finding that rapid expansion of their flocks without concurrent investments in measures to prevent disease, such as enhancement of biosecurity, has left them vulnerable to disease. Even smallholders with uninfected flocks have been affected as a result of market shocks when H5N1 HPAI occurred, as the public and authorities demanded infection free produce grown under "safe" certifiable conditions.

FAO argues that the very dynamic growth of the poultry industry world-wide, but particularly in regions which are lacking the scale of veterinary infrastructure needed to monitor and protect animal health has created a 'time bomb' that 'exploded' when H5N1 HPAI, a highly transmissible disease of public health significance, emerged. All poultry producers were affected by market crashes but those with sub-standard disease prevention programmes, across all production sectors, paid a particularly high price for their failure or inability to implement such measures. Some of these producers will never return to poultry production and those that remain may no longer have access to markets they relied upon before the outbreaks occurred.

Insufficient Attention to Managing the Health Risks Associated with Sector Growth

FAO has long noted with concern the rapid expansion of the poultry industry without the required veterinary support systems; this concern also relates to the growth of practices such as free grazing duck production in association with paddy rice systems and to the rearing of domestic birds over ponds in fast expanding aquaculture systems. FAO considers that such practices may be ecologically and economically sound but some of these production systems, in particular free grazing ducks, have now proven to be reservoirs of H5N1 virus. Therefore additional measures, such as effective duck vaccines and easy-to-apply vaccination technologies, need to be implemented for these important production systems to be safe and sustainable.

It is perhaps too easy to blame veterinary authorities for failing to impose tighter standards on producers when viewing events in retrospect, as the political will to implement necessary actions usually only materializes after major shocks have occurred that convert potential problems to real ones. Similarly it is rather easy to blame governments and donors for sponsoring programmes in many developing countries to encourage poultry raising as a viable income earning activity for rural populations; it is certain, though, that such programmes with their direct benefits particularly for women and children in terms of livelihoods and access to micronutrients (The World Hunger Project, 2005) need to be associated with the strengthening of disease prevention capabilities.

Although it is recognised that intensively reared poultry can play a role in the emergence of highly pathogenic avian influenza viruses, these farms can also remain largely uninfected in the face of infection in other production sectors through rigorous implementation of biosecurity and other disease prevention measures. This has been demonstrated in Thailand and Hong Kong SAR where poultry have been reared successfully in intensive farms despite the presence of virus outside these farms.

Live bird markets, available in most poultry farming communities, have been blamed for maintaining and spreading infection and there is little doubt that they pose major challenges to veterinary authorities, as seen in experiences from the US and Hong Kong. It has proven difficult to keep avian influenza viruses out of such markets, reason for which their continued operation is questioned by some experts and policy makers.

The Challenge for Advising on Safe and Equitable Sector Development

Achieving an appropriate balance between the benefits of enhanced biosecurity, the risks associated with creating large susceptible populations of poultry in industrial scale farms, providing consumers with affordable food and protecting the livelihood of poor smallholders and villagers is perhaps the greatest challenge facing authorities when making decisions relating to control of H5N1 HPAI. FAO's animal health programme continues to work in order to better understand the global epidemiology of the disease and to define the best strategies for prevention and control. To ensure that these strategies are socially and economically sound, FAO has set up a dedicated group of professionals to carefully analyse socio-economic impacts of the disease and of disease control measures and to advise countries and donors on the management of the challenges associated with control of this disease vis-á-vis the current and future structure of the poultry industry.

The current HPAI H5N1 crisis poses a possibly unprecedented challenge to the scientific community, both biological and social, to work together to bring the understanding of the socio-economic impacts of efforts to control HPAI to the forefront of the public and private debate. The question is how best to do this so that the risks and pathways of spread, the socio-economic impacts of control measures, and cost-effective control measures can be identified to minimize the negative impact on the poor while successfully containing the HPAI threat. More research has to be done to explain all the determinants of the epidemiology of the disease and to develop better tools, such as vaccines, and strategies to prevent and control avian influenza. Nevertheless, it needs to be recognised that decision makers will have to cope with making decisions under uncertainty for some time to come in that they will not have all the information they need about the disease when implementing control strategies and may need to modify these as new information becomes available.