IPPE: Vaccines and the Fight Against Avian Flu

US - Last year's outbreaks of highly pathogenic avian influenza in the US were devastating for poultry producers, but industry players used lessons learned from these outbreaks to help with control of the disease in this year's Indiana outbreaks.
calendar icon 22 February 2016
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At the 2016 International Production and Processing Expo in Atlanta, a seminar was held to look at the lessons that could be taken away from the outbreaks.

Dr David Swayne, Laboratory Director for the Southeast Poultry Research Laboratory in Athens, talked about the trends of avian influenza infections around the world, and how vaccination is used in some countries to help with prevention efforts.

Are outbreaks increasing?

Dr Swayne said that a list of avian influenza outbreaks over time suggests that there are more outbreaks than there used to be.

"For example, our current decade which is only five years old, we had ten outbreaks, compared if we go back into the 50's and 60's and 70's, we had very few outbreaks. There is definitely the appearance that we have had more outbreaks more recently than we have in the past," he said.

In particular, an avian influenza lineage that emerged in China in 1996 has affected poultry and humans in 70 countries and has killed in the region of 500 million birds. Scientists call this the 'Goose Guangdong' lineage of viruses.

Dr Swayne pointed out that avian influenza incursions in the US had been a major learning curve, and last year's outbreak in particular had showed all stakeholders how devastating it could be.

What strategies can be used against avian influenza?

Dr Swayne said that eradication is really the only strategy that can be used against highly pathogenic avian influenza, because industry cannot live with the disease and also produce the large volumes of high quality meat that consumers demand.

"Historically this has been handled by what we call 'stamping out' programmes and that's exactly what we went through in the Midwest last year, with the H5N8s and H5N2s, and also what we experienced as a controlled method for the H7N8 this year in Indiana."

Stamping out the disease involves a variety of components, including enhanced biosecurity and surveillance, so speedy action can be taken on infected farms, and depopulating all the infected birds.

Dr Swayne explained that unlike bacteria, viruses don't grow after the host is killed, so if you kill the birds, then the virus stops growing and it starts deteriorating from that point on.

Another important component is education, which involves making sure everyone in the supply chain knows their role in prevention and control of an outbreak.

A final weapon in the arsenal against avian influenza is vaccination.

"Vaccination has not been practiced worldwide; it has been used in some countries, not in others, and it can be used very specifically focused in some countries in certain conditions and aspects," Dr Swayne said.

How has the vaccination strategy been used in the past?

On a timeline of 39 epizootics dating back to the 1950s, Dr Swayne showed how 34 of them successfully used a stamping out programme to eradicate the highly pathogenic virus. The other five used vaccinations as part of the control strategy, together with stamping out.

Dr Swayne said an estimated 103 billion doses of highly pathogenic avian influenza vaccine were used between 2000 and 2010.

The top four vaccine buyers use the vast majority, with China coming in top using 91 per cent of the vaccines. Egypt, Indonesia and Viet Nam are the other top users.

Dr Swayne said countries have used vaccines in three different ways. Firstly, the top users implement a routine national vaccination programme.

Secondly, countries adjacent to infected areas have used vaccines in the border areas as a preventative measure to keep the disease out. These countries stopped using vaccines when the risk level fell again.

Thirdly, vaccines have been used as an emergency measure, when a bird flu outbreak has already occurred in the country, to protect other birds in that region. Again, vaccination use stopped in these countries when the outbreaks had been eradicated.

How can vaccines help?

Dr Swayne said that vaccination has an immediate impact on preventing disease outbreaks, and reducing mortality from the disease.

Because of improved resistance to infection, the virus does not replicate well in vaccinated poultry, so there's reduced replication, there's reduced shedding of that virus into the environment and it prevents illness and death of those vaccinated poultry.

However, he said there are limitations to the usefulness of vaccination.

A stamping out programme is likely to take longer to eradicate the disease if poultry in the affected country have been vaccinated, and Dr Swayne said that vaccination use is also associated with complacency. This means that it is sometimes harder to persuade farmers to practice strong biosecurity and quick eradication measures.

In addition, he said the vaccination programme is only as good as the quality of the vaccine, and the organisation of the programme.

Another negative aspect to vaccination is that it makes surveillance and diagnosis more difficult, as it is sometimes difficult to tell the difference between vaccinated and diseased birds.

What makes an effective vaccination programme against avian flu?

A good programme needs a very high-quality, high potency vaccine to produce a high response.

"Ten years ago when vaccination began in Asia, there were lots of companies making vaccines that were low quality," Dr Swayne said.

"You could take that vaccine to immunised birds, you could find no immune response or very little immune response, and those vaccines did not work. They make people feel good, but they don't protect birds."

The vaccine also has to be related to the virus found in the environment, otherwise birds will not be protected against the correct strain.

Resistance has emerged in viruses to the vaccines used to fight them, so vaccines have to be constantly modified to keep up with changes in the environmental strains.

Other aspects to consider are the types of birds being vaccinated, the geographical area, commercial or backyard flocks, and the need for booster vaccinations.

Dr Swayne said that the way to apply a vaccination programme effectively differs according to the conditions in that region.

He added that it is hard to use routine national vaccination strategies because of the difficulties of hitting all the birds, given the high turnover of the poultry industry, and targeted vaccination has proved the most effective method across the globe.

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