Avian influenza

Situation in Asia as of September 2004

The particular strain of highly pathogenic avian influenza (HPAI) designated H5N1, the cause of the pandemic, is known to have been present in several Asian countries and regions, including Cambodia, China, Indonesia, Japan, Lao People’s Democratic Republic, Republic of Korea, Thailand and Viet Nam, since 2003. Infection was probably introduced into one or more of these countries before the disease was recognized and international reporting started in January 2004. Pakistan has reported cases of HPAI H7N3 and low pathogenic avian influenza (LPAI) H9N2.

In June-July 2004, China, Thailand and Viet Nam reported cases in poultry. In August 2004, Malaysia reported its first case of HPAI H5N1 in poultry, China reported isolations of H5N1 viruses from pigs that were sampled in 2001 and 2003, and Viet Nam reported three fatal human cases of infection with HPAI H5N1. In September, Malaysia reported several outbreaks of HPAI H5N1 near its border with Thailand, while Indonesia, Thailand and Viet Nam continued to report cases in various poultry species. Thailand reported an additional human mortality caused by H5N1 infection. According to the World Health Organization (WHO), since the second wave began, Thailand has reported three human mortality cases caused by H5N1 infection, and Viet Nam five. In September 2004, deaths in tigers were reported to have occurred in a zoo in Chonburi Province, Thailand. Outbreaks of HPAI H5N1 in poultry in Asia are unprecedented in their geographical scope, rate of spread and range of susceptible hosts.

As countries in the region continue to implement control programmes and conduct scientific investigations, there is an increasing awareness of the significance of reservoirs of avian influenza viruses in wild birds, farmed ducks, live bird markets and, potentially, in pigs. The existence of such reservoirs has a bearing on the ability of governments to control avian influenza, including H5N1. While eradication remains the overall objective, countries are pursuing complementary measures, such as increasing biosecurity to prevent the passage of infection from reservoirs to farmed poultry. Where it is difficult to increase biosecurity, vaccination against HPAI to decrease the susceptibility of farmed poultry may be an option. However, vaccination should only be performed with an appropriate surveillance system in place.

The spread of HPAI H5N1 across national boundaries demonstrates that it must be managed as a transboundary animal disease (TAD). In response to the HPAI crisis in Asia, FAO has implemented Technical Cooperation Programme (TCP) projects. Following the country’s recent outbreak of HPAI H5N1, the Government of Malaysia requested assistance from FAO.

Avian influenza in Asia reported as of October 2004, ordered by date of first official reporting to OIE

¹ Official (OIE) and non-official information (ProMED, press agencies, FAO tracking systems, etc.)
² FAO: FAO representative in concurrence with government sources
³ LP: low pathogenic strain

FAO expert meeting on surveillance and diagnosis of avian influenza in Asia

An FAO expert meeting was held in Bangkok, Thailand, 21-23 July 2004, with the participation of experts from the World Organisation for Animal Health (OIE), FAO Reference Laboratories and other scientific and technical institutions. The objective of the meeting was to prepare guiding principles and minimum requirements for HPAI surveillance and diagnostic networks that can be applied by countries and regional networks in Asia. The use of vaccination was also covered. Responsibilities and activities of the national veterinary laboratories and surveillance teams that will participate in the network of the three Asian subregional projects (East, South and Southeast) were outlined. The principles and minimum requirements are also broadly applicable to other AI viruses. The guidelines may not be directly applicable to surveillance for LPAI viruses.^[4]

FAO Recommendations on the prevention, control and eradication of highly pathogenic avian influenza (HPAI) in Asia

The newly published Position Paper FAO Recommendations on the prevention, control and eradication of highly pathogenic avian influenza (HPAI) in Asia presents the main scientific and technical issues and recommendations on prevention, control and eradication of HPAI. It has been prepared with the contribution of several experts and government officials. The contribution of OIE experts and the recommendations of the OIE Terrestrial Code^[5] are of particular importance. However, it is important to note that these guidelines reflect the knowledge of HPAI in Asia today. As the disease epidemiology evolves and scientific knowledge and management tools become more comprehensive, management approaches may need to be modified. As such, these recommendations will be under continuous review.

The document includes the following themes:^[6]

Factors to consider in determining the appropriate strategy for control. The strategies chosen by veterinary authorities to control HPAI in countries, regions or compartments are determined by a number of factors, to be considered in light of the particular situation of the country, region or compartment, such as the level of infection; the presence of wildlife reservoirs; farming and marketing systems; likelihood of infection or reinfection in countries or compartments; involvement in international trade; animal health infrastructure; economic, political and social issues; public health issues.

Economic, political and social issues. The impact of HPAI has been distributed within the entire poultry market chain, affecting producers, consumers and employees in the retail industry. Conversely, the impact on geographic regions has been uneven, with some local areas losing more than 50 percent of their poultry. Various levels of assistance, in the form of compensation and credit, have been provided. The document considers economic appraisal, focusing on elements of a control strategy that can be included within an economic evaluation, and covers human issues that are important when planning a control strategy but are harder to value.

Disease control. Control of HPAI is achieved by reducing the amount of virus circulating in poultry and on farms. Measures such as stamping out, cleaning, disinfection and vaccination are implemented to reduce the amount of virus present. Additional measures, such as movement controls, enhanced biosecurity and, as appropriate, vaccination, are implemented to create barriers between uninfected poultry and foci of infection.

Surveillance and monitoring are key to the prevention and control of HPAI. Early detection of incursions of virus by targeted surveillance gives veterinary authorities early warning of a potential problem, providing for the proactive introduction of risk management measures such as enhanced biosecurity. To this end, FAO recommends a general strengthening of animal disease surveillance and more emphasis on timely reporting to OIE and other international (FAO) and regional organizations.

A precondition for effective disease surveillance and control is a competent, properly resourced and well-trained official veterinary service. Facilities must be available to provide rapid and accurate diagnosis of disease and detection of infection. In some countries, resources from international organizations and donor countries support important elements of the required infrastructure. FAO, OIE and WHO will continue to work with countries in the region to enhance the veterinary infrastructure and the capacity to prevent and control HPAI. It is important to invest resources in the development and improvement of systems for active disease surveillance and timely reporting to OIE. This enables early warning of incursions to the official veterinary services in the affected and neighbouring countries, greatly improving the prospect of successful eradication.

The spread of HPAI H5N1 across national boundaries demonstrates that it must be managed as a TAD, with the cooperation of countries in the region - ideally through the formation of regional epidemiological and laboratory networks. This does not mean that all countries must adopt identical control and response strategies. However, regional coordination, communication and harmonization of approaches to surveillance, diagnosis and control will enhance understanding and facilitate control of the disease. Control strategies for AI must be based on knowledge of the major pathways of spread of the viruses. HPAI H5N1 virus is mainly excreted via the faeces and respiratory excretion of infected poultry. Most commonly, transmission is via direct contact between birds, or through contact with the virus on fomites (clothing, shoes, equipment, etc.), or more rarely through airborne particles.

The use of vaccines. There is evidence that infection has been established in some parts of the region for some years and that the HPAI H5N1 viruses have become endemic in some countries. In response to this situation, some countries have commenced vaccination and others are considering the role that vaccines could play in their control programmes. A number of efficacious vaccines are commercially available. Based on field and laboratory evidence, these vaccines provide excellent protection against clinical disease in chickens, reducing mortality and the effect of the disease on production. Properly used high-quality vaccines confer good resistance to infection, so that the vast majority of vaccinated birds exposed to field virus do not become infected. For the few vaccinated birds that might become infected, shedding of virus is markedly reduced (both in the duration of excretion and the quantity of virus shed).

Vaccination reduces the total amount of virus contaminating the environment and acting as a source of infection to poultry and humans. However, the vaccine must be of high quality and have sufficient antigenic mass for the birds to develop a protective immune response. In addition to these technical considerations, governments must also consider the export issue as well as other non-technical factors in arriving at a decision to include vaccination as part of their control strategy. These factors include the social effects of widespread destruction of poultry on smallholder livelihoods and the economic consequences of failure to control the disease.

Adoption of the most appropriate control strategies. The strategy adopted by governments concerning their countries, zones or compartments is determined by the perceived importance of the disease politically, socially and economically. Issues that must be considered include public health, economics, sustainability of farming enterprises and adverse publicity associated with repeated outbreaks of the disease.

Conclusions. In determining the strategy for control of HPAI H5N1, all available control measures should be considered, and those that are feasible and likely to be cost effective in the local situation should be adopted. The selection of measures should be based on risk assessment and a thorough understanding of the HPAI status in the country or compartment. Stamping out and vaccination are not mutually exclusive strategies. Targeted vaccination has considerable value as part of a phased response strategy, allowing veterinary authorities to bring infection under control as a preliminary step on the road to eradication in specified compartments or entire countries, as appropriate to the circumstances.

FAO conclusions and recommendations. A tabulated summary of FAO conclusions and recommendations is provided as an annex to the document.