Professor Simon More:

On pre-movement testing, we carried out a study approximately 12 years ago which specifically investigated whether it would be useful in Ireland. It was a little akin to a cost-benefit analysis because there is a significant amount of effort involved in pre-movement testing. We looked at whether it would be of assistance in picking up more breakdowns. Our view at the time was that pre-movement testing would only be useful if implemented in a very targeted way, essentially focusing on high-risk herds. That was the conclusion of our study. I wish to make two broader points. In terms of first principles, of course, it would be useful for animals moving from a high-risk herd to be tested at appropriate times. Six months is probably an appropriate timeframe because it takes time for the infection to develop and return a positive test result.

I would like to digress slightly, if I may. I have concerns that in Ireland we make a lot of animal-based decisions. When we have an infected herd, we are essentially saying that if we do certain things, this group of animals is safe but that another group is not so safe. I would have concerns that we are really stretching the ability of our tests to do that. If we were to move to a risk-based situation, it is much safer to work at herd level and to say that all of the animals in the herd are of equivalent status whereas pre-movement testing looks at the individual animals. Let us say an animal is infected. The probability for picking up infection with a skin test is, on average, 50% but it will generally be higher later in the course and much less if it earlier in the course. Everything helps but the fundamental question is whether we are doing enough.

On whether there are any other options apart from risk-based systems, to be honest, based on all of the evidence that I have, I cannot see how we can eradicate the disease within a reasonable timeframe without a really robust risk-based system, which would probably need to include trading, unless we get a better test. On deer, the question was asked as to whether there is evidence anywhere of infection drifting from deer to cattle. I spoke at length about this with my colleague from Michigan, Dr. Dan O'Brien, who has been extremely helpful. He works for the wildlife department there and has been very involved in its TB eradication programme. I asked the same question of him. The authorities there are very confident that white-tailed deer in Michigan are a maintenance host which spill back to cattle. They found evidence of TB in deer populations where there could not have been cattle involvement. I do not think we would ever get that here in Ireland because deer and cattle coexist. Our best hope is probably whole genome sequencing although the organism that causes TB is problematic. In terms of whole genome sequencing, if an organism is passed from A to B, for example, the organism mutates as it shifts across. If I know the direction of mutation, I will know it has moved in that direction. Most organisms change quite frequently but the organism that causes TB might only change once every two years according to experts at UCD, Professor Stephen Gordon and Mr. Joe Crispell, who are leading this work. That makes the work very difficult but nonetheless, as I have highlighted in my paper, there is work from New Zealand and just published work from the USA that would suggest that we are starting to get evidence about directionality that will help us.

Deputies asked how the disease is transferred. It can probably be transferred in lots of different ways but the way that is most likely is through the sharing of aerosols. In order for the organism to establish infection most effectively, it must be what is called a droplet nuclei, which is the way it is presented when an animal or person breathes out. If an animal breathes out and if it has the infectious material, when a nearby animal breathes in, the infection is in a form that allows it to go all the way down to the lowest parts of the lung. My expert colleagues believe that one might only need ten organisms to establish infection if it is presented that way whereas one might need 10,000 or 100,000 organisms for it to establish by way of ingestion. It is really an issue of risk. It is my understanding, based on best principles because we do not know everything about TB, that sharing pasture and other close contact, particularly when there is an opportunity to share aerosols, is probably the most effective way for the disease to spread. We certainly cannot say, including for badgers, that sharing pasture or cattle grazing near a latrine is not possible but it is probably an issue of how frequently it occurs, the dose of the organism that is present and so on.