Is the time coming when we shall have chickens which can resist bird flu? Poultry International interviews Dr. Laurence Tiley, who is leading a multi-institute British research project to develop chickens with genetic resistance to the avian influenza (AI) virus. In partnership with Dr. Helen Sang at the Roslin Institute in Edinburgh, Scotland, the project explores the potential of introducing specific resistance traits using genetic modification technologies. Dr. Tiley is senior lecturer in Molecular Virology at the University of Cambridge in the UK.
PI: Dr Tiley, what is this research?
Tiley: We are investigating strategies to produce chickens that are genetically resistant to infection by AI virus. We are looking at both natural resistance mechanisms and novel mechanisms that can be introduced by genetic modification methods. We are developing strategies that will work against all strains of the virus (highly pathogenic and low pathogenic) and which will be difficult for the virus to escape by genetic adaptation.
PI: Why avian influenza?
Tiley: For several reasons. Firstly, I have had a long-standing basic research interest in the molecular mechanisms controlling influenza virus replication. I saw an opportunity to move my research out of the laboratory into a more applied situation when I read about Dr. Helen Sang's research at the Roslin Institute which has led to the development of the key technology necessary to put this into practice.
Secondly, AI is a major global concern right now. We are in the midst of the largest international outbreak of highly pathogenic avian flu ever recorded. Hundreds of millions of birds have been slaughtered in the ongoing attempt to control the H5N1 epidemic. This has caused considerable hardship and suffering for poultry producers.
Additionally, there is the very worrying ability of this virus to jump species and the possibility it could cause the next influenza pandemic in humans. We now realise that chickens are a potential bridging species that can facilitate novel strains of influenza jumping from wild birds to humans. These factors provide a strong incentive to investigate novel ways in which the disease can be controlled in chickens.
Thirdly, I believe genetic modification (GM) has great potential for generating disease-resistant animals. A lack of popular support and public distrust of GM-derived foods has meant this particular approach to disease control has been rather sidelined in Europe and the US. However, avian flu is something that the general public is concerned about and can appreciate the potential benefits that GM can offer. Our hope is that, by demonstrating the potential of GM for producing resistant chickens, we can begin to dispel some of the reservations the public have about this technology.
PI: So, is the suggestion that, at some point in the foreseeable future, most commercially-bred poultry are likely to be genetically resistant to the avian influenza virus?
Tiley: That is our objective and it is realistic in the foreseeable future.
PI: Are there reasons for believing that a natural ability to resist the virus exists in the genetics of some birds?
Tiley: There are almost certainly genetic traits that will reduce susceptibility of chickens to AI, although I doubt it will be possible to produce completely resistant birds by selective breeding alone.
We have been looking at the gene for a protein known as Mx. The mouse Mx protein (Mx1) is highly protective against influenza virus in mouse models of the disease. Unfortunately, the Mx gene of chickens appears to be inactive. There has been a flurry of interest in one particular polymorphism of chicken Mx that was thought to be active against influenza virus. However, our experiments on this protein have not been encouraging. Nevertheless, it is certainly worth looking further at Mx and searching for other genetic resistance loci.
We strongly favour the use of genetic modification approaches. One possibility is to introduce the mouse Mx gene into chickens. We are also introducing novel genes by GM into the chicken that are specifically designed to target AI. These do not exist in chickens, so it is not possible to introduce them by selective breeding. Potentially, any natural genes that are identified in genetic studies can also be introduced by GM methods. This has the advantage of being able to introduce the gene of interest precisely into your founder lines without bringing in any other unwanted traits. The potential is enormous.
PI: Is this in all types of poultry or in waterfowl, in broilers or in layers?
Tiley: Our GM strategies could be adapted to broilers, layers, turkeys, ducks, quail and even pigs.
PI: Are there or have there been other projects with a similar objective and, if so, how does your project differ?
Tiley: Poultry companies and other research groups are trying to identify genetic traits that might enhance resistance to AI. This is where some of the interest came from in exploring chicken Mx.
Our strategies include using inhibitory RNA molecules known as micro RNAs which block the virus's ability to produce proteins essential for its replication in the cell.
We are also using decoy RNAs that prevent the virus replication machinery from interacting with the viral genome. The virus replicates the decoys instead of itself. In addition to our interest in Mx1, we have several other strategies under development.
Although we have reached a fairly advanced stage with some of our GM chickens, we are not complacent and realise that we have some serious competitors. There are other groups exploring GM approaches similar to some of ours. However, we are pursuing a combinational approach with multiple inhibitory strategies which we believe is crucial to achieve robust resistance.
PI: How far has the project progressed?
Tiley: We have generated GM chickens carrying two different inhibitory genes and are testing these. We are currently investigating how the level of protection can be enhanced and have also just received further funding in Britain from the Biotechnology and Biological Sciences Research Council to continue our development of some novel GM approaches that we expect will be even more effective.
PI: Are you confident that this research will yield results that can be applied commercially and what sort of commercial application do you envisage?
Tiley: Yes, I am confident. I envisage that we will identify an effective combination of inhibitory genes that can be introduced into multiple founder lines of chickens by GM and bred through to production birds by conventional methods.
PI: In your view, how soon might we expect to see the outcome of this research in the breeding of the poultry we use around the world? Might it be on a regional basis according to endemic risk?
Tiley: We are still a long way short of showing the degree of protection that would be required to justify repopulating the commercial chicken industry with GM chickens.
Once we have achieved this level, I expect the introduction would be regional, with China and South-east Asia being the likely pioneers. It is certainly a realistic possibility in the next 5-10 years.
PI: What major challenges remain to be resolved?
Tiley: Increasing the level of protection. Expanding the range of protection to include other avian viruses such as Newcastle disease virus and Marek's disease.
And, dispelling the public's reservations about GM.
PI: Genetically, are there trade-offs involved in breeding poultry to be resistant to avian influenza and what would these be?
Tiley: Specific introduction by GM technologies should avoid the negative trade-offs inherent in selective breeding.
By modifying multiple founder lines, rather than relying on a single GM line, we should avoid the potential problems associated with "bottlenecking" and loss of genetic diversity.
The biggest trade-off is the potential stigma of the GM label. This is something that will take time to overcome, but eventually it will happen.
PI: What other commercially valuable traits in poultry hold promise for additional research and does poultry genome mapping make it possible for genetic progress to proceed rapidly on a number of fronts or traits simultaneously?
Tiley: My interest is restricted to viral diseases and I have already mentioned NDV and Marek's virus.
Once GM gains acceptance, the potential for preventing infectious diseases in poultry is considerable. However, figuring out the best way to tackle some of the other pathogens is not a simple task.