Avian Influenza
International Federation for Animal Health
Global news headlines are filled with reports about the spread of avian influenza, or “bird flu,” and the possibility it could become a global pandemic in humans. The animal health industry, which researches and produces a range of products to prevent and treat disease in animals, has worked with government authorities, stakeholders and poultry producers and developed vaccines that can help address the spread of this disease in poultry.
Although avian flu has primarily been an animal disease to date, experts fear the virus could mutate into a form that could be spread among humans. While governments around the world are justifiably preparing for the possibility of a human pandemic, it is important to realize that the best protection for human health is the control and eradication of the disease in animals. The threat of avian flu spreading to humans is a clear demonstration of the interrelationship between animal health and human health, and the important role animal health and animal health products can play in protecting public health.
Background
Avian influenza (AI) is a respiratory disease of birds caused by a virus. There are several different types. Outbreaks of low pathogenic avian influenza (LPAI) are common around the world. The high pathogenic avian influenza (HPAI) is more serious due to its higher mortality rate in affected birds. The type currently spreading in Asia and in wild birds in Europe is referred to as H5N1 HPAI. The “H5N1” designation comes from the arrangement of two proteins on the surface of the virus.
Avian flu is transmitted from bird to bird within a flock or poultry house mainly by inhalation of the airbourne virus and by contact with the virus shed in the faeces from infected birds. It can be transmitted from poultry house to poultry house by contact with contaminated equipment or the movement of people who can carry contamination on their clothing and footwear. While the most common hosts for the virus are wild waterfowl species, it also has been reported in many common species of poultry, including chickens, ducks, turkeys, geese, pheasants and quail, as well as in a variety of other birds like parrots, cockatoos, and parakeets. Some species are more resistant to infection or can be asymptomatic transmitters of the disease.
Animal Health Products to Help Control AI
A number of animal health companies produce vaccines that are effective in preventing clinical disease in birds. These vaccines help control the spread of AI by increasing the resistance of the vaccinated bird and by reducing shedding of the virus by infected birds.
AI vaccines are currently being used in South America, the Middle East, Asia and in one EU member state (Italy).
Vaccine use is generally controlled by government policy. Internationally, the Food and Agriculture Organization of the United Nations (FAO) and the World Organization for Animal Health (OIE) are the two main organizations responsible for monitoring and controlling animal diseases internationally. Guidelines for vaccination use, surveillance and control can be found at http://www.fao.org/ag/againfo/subjects/en/health/diseases-cards/special_avian.html.
Animal health companies also contribute to the control efforts of avian flu with their wealth of knowledge in the field, products to control disease vectors and, not least, by strictly following sanitation measures when visiting farms.
The Manual of Diagnostic Tests and Vaccines for Terrestrial Animals of the OIE describes the presently available vaccines types and prescribes the standards for these vaccines. Information on the standards for AI vaccines can be found at http://www.oie.int/esp/normes/mmanual/A_00037.htm.
Vaccines: A Tool in the Fight Against HPAI
The Animal Health industry is actively involved in working with regulatory authorities, stakeholders and poultry producers in efforts to eradicate AI. It is recognized, however, that vaccination alone is not sufficient to prevent the spread of this disease. The AI vaccine, like human flu vaccines, does not prevent the virus from infecting the vaccinated individual. However, it does protect the bird against clinical sickness and death associated with the disease and helps reduce the chance of new outbreaks by reducing the shedding of the virus from infected birds. A concern associated with vaccination is that vaccinated birds may still become infected. Such birds may not have clinical signs and thus disease might be missed in a flock, possibly becoming endemic. Modern vaccines that reduce viral shedding and spreading of virus in vaccinated birds reduce these risks. The level of effectiveness of the vaccine will also depend upon the virulence and pathogenicity of the particular virus.
An effective AI control/eradication program rests on three important legs:
1. Preventing exposure to the virus in poultry by means of biosecurity controls, such as a set of procedures designed to protect poultry populations from exposure to the virus. In countries with large commercial poultry operations, the birds are typically raised in enclosed buildings designed to provide protection from various types of disease carriers, but once the infection has taken hold in a flock it can spread quickly throughout that building. The spread of the disease has been facilitated in Southeast Asia by the fact that chickens, ducks and other poultry often run at large in the villages in close proximity to each other and to people, whose clothing or footwear may inadvertently transport the virus from one bird to another.
2. Rapid culling of infected birds. Since most poultry flocks are free from AI, the generally accepted response when an outbreak has occurred is to stamp out the virus by eradicating the affected flocks.
3. Vaccination, which can be effectively used as part of an eradication program to stop the spread of the virus. Vaccination reduces shedding of the virus by the bird, both in terms of the period of time of shedding and the concentration of the virus shed. Vaccination, as one component of an effective control program, has been shown to be successful in helping to eradicate the virus in several countries. Vaccination of free range birds where appropriate is an extra tool, in addition to other biosecurity measures, to stop the virus from moving from wild birds into the commercial poultry industry and from there to infect poultry workers.
The proper timing and combination of these three tools are decided under the direction of local and national authorities. Globally and on a country-by-country basis, the animal health industry is working with and will lend all possible assistance to the authorities in the battle against this serious disease.
November 2005
Other resources:
Food and Agriculture Organization (FAO) at http://www.fao.org/ag/againfo/subjects/en/health/diseases-cards/special_avian.html
World Organisation for Animal Health (OIE) at www.oie.int/eng/en_index.htm
World Health Organization (WHO) at http://www.who.int/csr/disease/avian_influenza/en/
European Commission DG Health and Consumer Protection at http://europa.eu.int/comm/dgs/health_consumer/dyna/influenza/index.cfm
United States Department of Agriculture at www.usda.gov/2005/10/0459.xml
United States Government information at www.pandemicflu.gov
