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DAHS Poultry Topics Feature Article, 25 June 2009

Avian Influenza Threats Highlights the Role of Effective Biosecurity

Since December 2003, devastating outbreaks of Avian Influenza have decimated flocks of poultry in many countries, forcing a radical review of biosecurity measures.  The consequences of Avian Influenza are immediate and financially severe.  However, with thought and planning, a comprehensive biosecurity system can be implemented in order to minimise the impact of further catastrophic outbreaks. 

Disease control strategies must be a priority for governments and poultry producers alike.  Once implemented biosecurity must be rigidly enforced.  During the devastating Dutch Avian Influenza outbreak of 2003, the Dutch veterinary authority (RVV) instigated tough biosecurity measures to bring the crisis under control. 

Transmission of the virus has been strongly linked to moving live birds, contaminated carcasses or litter in vehicles and has highlighted the importance of vehicle-related biosecurity.  Producers have often had difficulty in justifying this action as time must be spent ensuring that vehicles are adequately disinfected which may have a commercial impact on the producer.  However any vehicles or associated equipment coming into contact with poultry or litter may become grossly contaiminated with organic material containing  large number of infective bacterial and viral particles. 

Although notoriously difficult to police, vehicle disinfection protocol can help to reduce the potential spread of the virus.  The guidelines include:

  • Wash wheels and wheel arches between visits
  • Avoid walking onto a farm unless your footwear has been disinfected by use of foot bath or similar
  • Use protective clothing as supplied by the farm
  • Follow the site's own biosecurity instructions
  • Clean and disinfect vehicles after each journey, including the driver's cab 
  • Use a combination approach to first clean and degrease the vehicle and all contaminated surfaces, followed with the use of a disinfectant with proven activity against the pathogens of concern to the particular enterprise
  • Use products with known efficacy in removing biofilms from surfaces.  These may be difficult to clean and can harbour and protect many microorganisms
  • Wash and disinfect the vehicle at the end of the day

The purpose of such strategies is twofold.  In the first instance they will help to deal with the disease emergency as it happens and secondly play a major part in maintaining a high standard of biosecurity on an ongoing basis.   

Leading poultry veterinarian, Stephen Lister MRCVS, recommends that poultry producers and government maintain their guard and a high state of preparation in readiness for any new threats of Avian Influenza.  "A cornerstone of preparation against Avian Infleunza must be to maintain a constant state of vigilence against the disease.  Control protocols should be based on sound and effective continuous biosecurity appropriately applied." 

Avian Influenza has no respect for geographical borders and can affect all species of birds.  In order for any control strategy to be implemented effectively, legislators must have a clear understanding of the location and density of flocks per square metre in the region, as well as the exact type of poultry involved (housed versus free range, turkeys versus ducks).  This information is critical and needs to be accurately and promptly distributed throughout the industry.  It will assist in the swift and effective tracing of animal movement. 

Due to a natural resistance, free living birds may carry the influenza virus without becoming ill however, they are still capable of transmitting the virus to domestic poultry.  In intensive poultry rearing systems, young turkeys and laying hens can be extremely vulnerable.  In many cases it will be necessary to reduce the risk of further contamination by the prompt slaughter of stock while still on infected premises.  Most countries already adopt a rigorous stomping out policy to control disease however, this can prove difficult depending on the number of birds involved and the type of housing.

There is now an over-riding requirement that all methods of slaughter should be humane and ensure the highest standards of animal welfare.  Methods used include lethal injection, which may be feasible in small flocks only, neck dislocation which may be possible in flocks up to 10,000 birds, toxic agents via the feed in which a reduced food intake and palatability problems must be a consideration, and mobile killing lines.  The dampening of carasses and litter with disinfectant prior to removal may help to avoid a further spread. 

An infected premises can pose a high risk to neighbouring farms and information gathered from the recent Dutch outbreaks suggest that strong winds and dry weather can be responsible for spreading contaminated dust over a vast area.  Spread by faeces or contaminated litter is also considered to be a significant factor and can be aided by air, personnel, vehicles and equipment.  Once such risk factors have been identified, it is the responsibility of the poultry producers to rigidly enforce the necessary biosecurity measures.  Methods to consider are:

 

  • Maintain an effective perimeter control
  • Implement disinfectant foot dips and protective clothing
  • Avoid stock coming into contact with wild birds
  • Most importantly, ensure regular and thorough cleaning and disinfection of poultry houses

It should be noted that Avian Influenza virus survives well in water so simple washing with water alone may assist transmission.  Disease control experts in government agencies worldwide have regularly selected broad spectrum Virkon® S as a disinfectant of choice.  Dutch authorities invoked its use across all farms with up to three applications during the 2003 clean-up process.

A disease outbreak such as Avian Influenza will often be accompanied by a ban on animal movement, which if prolonged can create severe welfare problems.  Experience has shown that it is vital that plans are put into place to allow for the relaxation of movement restriction as soon as possible.  This should be followed by the swift transportation of eggs to hatcheries and packing stations, chicks to hatcheries and farms and commercial stock to processing plants. 

Once an outbreak has been bought under control, the industry can start to restock its flock.  Care must be taken that this process is monitored and controlled.  The success of repopulation is dependent upon good quality stock therefore all sources of poultry must have a healthy status to ensure the good health of any bird which is reintroduced

It is almost impossible to assess the cost of not implementing biosecurity measures.  With over ten million birds lost in the Dutch Avian Influenza outbreaks the cost exceeded 150 million Euros.  In the 1983 Mid-Atlantic outbreak of Avian Influenza, the federal govenment incurred costs of over $62 million in their efforts to eradicate the disease.  Producers lost $200 million due to increase flock mortality.  However realistic any compensation system might be, companies both large and small are frequently forced out of business.  Government and industry representatives were in agreement that the Mid-Atlantic outbreak could have been radically reduced if better biosecurity measures had been implemented. 

As a result, Mid-Atlantic Cooperative Extension (MACE) was formed and produced various educational materials on biosecurity, however it has proved difficult to distribute this material to non-poultry personnel who regularly visit poultry operations and are in a prime position to transmit disease causing pathogens.

Needless to say, anyone who directly or indirectly deals with poultry has the potential to spread the disease.  With this in mind, the industry needs to be in a constant state of preparedness based on sound and effective biosecurity.

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