For the first time scientists say they could have the answer to eradicating TB in Ireland – and there’s no reason why Northern Ireland couldn’t also be on the path to solving its TB woes.
But it could mean that a radical movement system – similar to what is used in Australia – could be necessary on the island.
Speaking at the Agri-Food and Biosciences Scientific Outlook in Co. Antrim, Prof. Simon More from University College Dublin (UCD) said decisions made now on the disease would have “huge implications for the future”.
Currently, he explained, the Republic is around 70 years away from completely eradicating TB – something that could be expedited by future research on how TB spreads to lower the reproductive rate of the disease.
The basic reproductive number (R0) determines the future of an epidemic. It is the average number of secondary infections produced when one infected individual is introduced into a host population.
Culling and vaccination programmes
He said: “What’s happened over the last six months [in the Republic of Ireland] has been incredibly important – and, I believe, ground-breaking for us – in that we have made a substantial advance with the introduction of badger vaccination.
“We now have the results of the large multi-year study in Co. Kilkenny, which has shown that – if on top of everything that we already do – if we introduce badger vaccination as well we can actually drive that reproductive ratio lower.”
Prof. More said that, for the first time ever, scientists “really genuinely” have the tools to eradicate the disease – but there’s a but.
“We are at a critical point in the Republic at the moment. At the moment if you introduce badger vaccination, we drive that reproductive ratio below 1 – but not very much lower – and so what that means is that if it’s just below 1 it will probably take about 70 years to eradicate.
Even though we have the tools to do it, it will take a long time.
“For us to move towards eradication we need to drive the reproductive ratio even lower and there’s really only two options – one is further, more intensive culling pressure on badgers or potentially another wildlife species and the second is radical controls. The former really is not possible so we are really looking at the latter.”
Recycling infection
In Australia – More’s home country, where TB has recently been eradicated – herds were ranked for their TB risk and can only buy from herds with equal or better TB status and can only sell to herds with equal or worse TB status.
“Movement is a big issue – essentially what is happening – we are recycling infection from herd to herd,” More said.
The theory appeared to be backed up by a figure later cited by AFBI’s Dr. Andrew Byrne who said that there had been 21.9 million movements in the database for 6.2 million cattle over the last 10 years in Northern Ireland alone.
More added: “The Australian approach is now relevant. I don’t think it was relevant in the South until transmission from wildlife was resolved.
Risk in Australia was assessed at the herd level, not the individual level,” he said. “The controls on infected herds became more and more draconian as time went by.”
In Australia the view was held that a herd remained ‘risky’ until every animal present at the time of the breakdown had gone.
Future implications
More showed a graph with the number of BVD ‘Persistently Infected’ (PI) animals plotted over time. It showed that large numbers of PI animals were retained in the first two years of the programme.
“If that had continued essentially we would have never eradicated BVD but if we could turn around the PI story and resolve PI retention then we could eradicate about four years later than if there had never been any PI retention in the first place,” he said.
“It’s exactly the same with TB – decisions now about how hard we push the system will have implications for many years to come.”
Challenges
“The key challenges I see for us in the Republic are all about monitoring.
“The key programme has been rolled out county to county – but, into the future, the focus will be on the reproductive ratio of the disease in badgers and cattle in different parts of the country so we will all be on monitoring programmes.
“The current focus in Ireland – and I suggest it’s the same here – is that we seek to make decisions on individuals. So we have a herd with a breakdown, we say these ones are infected and these ones are not.
“These ones can trade and these ones can’t.
“There is residual infection, there are animals that are infected that will not test positive to current tests. Also we know that herds that are infected will have a prolonged period of heightened risk of breaking down again.”
