Avian influenza… to vaccinate or not?

The public interest in AI shows no sign of diminishing, especially with the recent spread into Turkey and Romania. There has been much talk over contingency planning and the readiness (or otherwise) of the Government, Health Service, veterinary experts and the wider poultry industry.

This planning falls into two main areas. Currently, the most urgent is action designed to stop infection entering the UK in the first place. If that should fail then questions being asked move to how we would deal with an outbreak. With images of Foot and Mouth Disease still fresh in peoples minds, where large numbers of sheep and cattle being killed and burnt were seen on our TV screens, the public and industry would not be prepared to see this repeated for poultry on a large scale.

So what are the options? Is vaccination the answer?

A changing situation

One question being asked is why has there been such an acceleration in the number of virulent AI outbreaks and their rapid spread? There were only 18 outbreaks reported in the 40 years from 1959 to 1999 leading to the death of 23 million poultry, increasing to a further 15 outbreaks in only the last 4 years, with over 200 million birds lost. Although the answers are not clear, three significant changes are certainly contributory:

1/ An increase in the number and size of densely populated poultry areas (DPPAs) around the world, especially in areas where humans have a close relationship with poultry.

2/ A big increase in more extensive production systems.

3/ Possible global warming effects, changing wild bird migratory routes and periods, and even the species of birds migrating.

These factors are important in considering how we would cope with an outbreak of avian influenza.

Is stamping out the answer?

The recent Newcastle disease outbreak in pheasants in Surrey gives us a good example.

Although the outbreak was in an area where there were reported to be some 250 backyard flocks, this was a commuter belt, in an area of low density of commercial poultry. In addition, the source was rapidly identified by Defra, the site was quarantined and infected birds killed quickly. In such an outbreak the traditional “stamping out” policy proved very effective.

So how would we deal with a major outbreak?

If an outbreak of Newcastle disease or avian influenza occurred in one of the several DPPAs in UK then we may not be that fortunate. The first aim would be to limit the size and spread of any outbreak. This could be achieved by:

1/ Implementing good and effective biosecurity.

2/ Having effective early warning systems for infected flocks.

3/ Using quick and effective methods of diagnosis.

4/ Identifying the high risk areas and developing contingency plans.

5/ Improving our outbreak management (with good communication between the industry and Defra being paramount).

Control and prevention

We have to appreciate that no universal solution exists. Actions will need to be taken in the light of local knowledge, the route of introduction of infection and where it hits first. It is likely that a combination of strategies would be needed. It is clear that stamping out (prompt killing and disposal of infected flocks or high risk direct contact flocks) would still play the most significant part in control.

So what is the role of vaccination?

The first question Government and the industry needs to answer is what we would be trying to achieve with vaccination. The three main advantages of using the right vaccine and vaccination programme are to:

1/ Prevent clinical disease.

2/ Reduce flocks’ susceptibility to field virus (i.e. reduce the likelihood of flocks picking up infection)

3/ Reduce virus shedding and hence spread from infected flocks.

All these factors would reduce virus spread and the number of flocks that would need to be slaughtered.

Hence, vaccination could play a significant part in eradicating influenza from the UK in the event of a spreading outbreak. However, it must be managed appropriately—vaccinating and forgetting about other control measures would be a disaster. The main reason would be complacency and relaxation in biosecurity. Also, our trading partners may refuse to accept poultry meat or products from us if we opt for vaccination. Furthermore, vaccination could reduce clinical disease without necessarily eliminating the virus.

On balance, a properly implemented vaccination policy targeted at high risk groups in specific areas could be a very powerful tool in controlling an outbreak, as long as the vaccines were safe and efficacious (ie they work). Such vaccines should have ‘markers’ that allow differentiation of infected from vaccinated flocks (the so-called DIVA approach, done on blood testing).

So to vaccinate or not?

If we are unfortunate enough to suffer a potentially severe outbreak of avian influenza in the UK in the near future then it is likely that vaccination offers the possibility of a potent weapon in limiting spread and helping to eliminate the disease and the virus. This could help to reduce the commercial, social and animal welfare impact of the disease as long as the approach was targeted and used as part of a wider control strategy. This requires the availability of the most appropriate vaccines, with adequate stocks of such vaccines and contingency plans for their prompt and targeted application.

The debate on vaccination highlights the need for a coordinated and holistic approach to disease control—coordinated between Government, Defra, the veterinary profession, poultry companies and individual producers.