Bovine tuberculosis (bTB) is an infectious disease of cattle (Bos primigenius) caused by the bacterium Mycobacterium bovis. You could follow my ‘tuberculosis’ tag.
This disease is zoonotic. That is, M. bovis can infect us as well as cattle. Not very often, with modern food processing (pasteurised milk), but in theory it could still happen. That’s why British taxpayers’ money is spent on slaughtering cattle whose bTB tests come up positive.
Other animals can get bTB too. In Britain, some people think the native badger (Meles meles) is a reservoir of bTB, so badgers are being shot. In New Zealand (NZ), the non-native brushtail possum (Trichosurus vulpecula) was identified as a bTB reservoir, so possums were poisoned. When people speak out for a cull of badgers here in the UK, they often mention NZ possums.
Here’s what the NZ Department of Conservation (Te Papa Atawbei) says about their possum control programme. They’ve had great success over there by spraying with a broad-spectrum poison called 1080 (sodium monofluoracetate) which, here in Britain, can be used only in restricted areas such as sewers.
One of my favourite sources of bTB information is bovinetb.info. That site’s unnamed author says, ‘My motivation comes from wanting to create a web site which informs rather than one which tries to influence opinion. As such I try not to hold back any information which I think is relevant and I try to present information without bias.’
Here’s what that author tells us about bTB in NZ. You can scroll down for two graphs showing how, since the late 1990s, the number of bTB-infected cattle herds has fallen dramatically in NZ while it’s risen with equal drama in Britain.
It’s important to notice that the brushtail possum isn’t native to NZ. It was introduced from Australia in the 1830s for its fur and by now, it’s become a pest there. So I don’t think many people would mind if you got rid of all the possums in New Zealand. A very different matter from the badger in Britain, which has been a protected species since 1992.
At the end of the bovinetb.info article, you can read part of a 2009 email from Paul Livingstone of the NZ Animal Health Board (AHB). AHB ‘receives 63% of its funds from industry and 37% from Government.’
Dr Livingstone said, ‘There are three components to our TB control programme – Test and slaughter (with a high degree of intelligent retesting of test-positive animals based on epidemiological analysis); Movement control (both at a herd and area level) and wild animal control. The latter element has been the critical element that has seen our infected herd numbers reduced by over 90% in the last 12 years… the main reason for TB in cattle and deer herds in New Zealand is due to Tb possums [and sometimes…] ferrets… wild animals are the source of infection for over 80% of our infected herds…
‘TB possums (and other wild animals) have been identified in… about 38% of New Zealand’s land area… possums are a non-native… pest in New Zealand and thus we are able to kill them… [so] we have eradicated TB from [several] areas through targeted killing of possums… where TB possums are still present, we undertake control to maintain very low possum densities such that spread of infection from possums to cattle is significantly reduced. This is the reason why the New Zealand programme has been successful…
‘With regard to the UK and Irish TB control programme, it is possible that reducing overdue tests may assist… but in my considered view, this would be insignificant alongside your main source of infection for cattle, which is the badger…’ [Dr Livingstone doesn’t say what evidence he relies on to support his belief that badgers are the main source of infection for cattle. Here in Britain, that’s a controversial opinion. I’ll blog about it another time.] [So I did.]
‘Given that in the UK you are not able to control badgers, vaccination of badgers against TB appears to be your only option (vaccination of cattle has so far not shown to be efficacious).’ [I’ll write more about the vaccine we have, in later posts on Science on the Land.] ‘I note that your government is starting a badger vaccination programme, though catching and parental [injected] vaccination of badgers. The AHB and Otago University in New Zealand have developed an oral TB vaccine… fed to possums in baits… The oral vaccine has already being evaluated in Ireland and seems to be relatively efficacious… Further research is currently being undertaken in Ireland… it will take about 3 – 4 years to gain sufficient information to register the vaccine for use in badgers in the UK and Ireland. However, to eradicate TB from badger populations through vaccination will mean annual vaccination of badger populations for some 4 – 5 badger generations or around 20 years…
‘New Zealand farmers fund and are deeply involved in all aspects of the TB programme [whereas…] UK farmers don’t appear to want to be involved – especially don’t want to pay. Once farmers accept that they should pay, then they can start having a say in the form of the programme. From the New Zealand experience, it wasn’t until farmers started paying and taking responsibility for the programme that it started making progress…
‘[After…] 35 years of involvement with New Zealand’s TB control programme… I suggest that you should direct your attention to using all means at your disposal to keep badgers separate from your cattle until such time as you know though vaccination or other means, that they no longer pose a risk to your herd.’
This story is what Steve James of the National Farmers Union in Wales (NFU Cymru) was talking about when he said, ‘In New Zealand it was possums.’ He didn’t explain how the brushtail possum is different from the badger. Now, learning from bovinetb.info, I hope I’ve made that clearer.
Meanwhile, we’re taking Dr Livingstone’s advice about trying out badger vaccination. The BBC says that a trial of parental badger vaccination will start in Cornwall within the next few days. Will it turn out to be useful? There’s disagreement about what to expect. When I see news, I’ll tell you.