Wednesday, April 25, 2012
Zoonoses - they affect humans.
This week has seen a media frenzy after a Cornish alpaca owner was confirmed as suffering from ‘bovine’ tuberculosis. We have been 'banging on' about the risk of so called 'bovine' TB to other mammals for as long as this site has been online. Testing cattle and slaughtering those that react to exposure to bTB is missing the point. Where has that exposure come from, and what else may have been exposed to the same source? Animal Health Officers say that up to 90 percent of bTB breakdowns in Cornwall are caused by badgers. Even Professor Donnelly's electronic abacus is now indicating that up to 70 percent of cattle breakdowns in the RBCT proactive areas are badger related. We will blog that work later, but for now, we top up with an overview of Dianne Summer’s news, released last week on her website that she has contracted ‘bovine’ TB.
Over the past years, we have reported the disease in cattle herds which have not bought in animals for decades and the spill-over of bTB into other species including free range pigs, alpacas, llamas, sheep and goats. The disease has also been increasing steadily in domestic cats and dogs.
Like the small cage-birds taken by miners into coal mines last century to warn of deadly ‘firedamp’ gas, regularly tested cattle act as ‘canaries’ - sentinels of the amount of bacteria in the environment, available to infect many other mammals, including human beings. In 1986, the ministry slaughtered 700 cattle. By 2007 our ministry culled 28,000 and figures from the last couple of years have approached 40,000. The message of these sentinel ‘canaries’ is being ignored.
Spillover of bTB to other mammals is not helped by the way Defra presents its statistics either. While their figures for cattle bTB outbreaks are fairly comprehensive - as long as their new computer isn't on strike - figures for other species are presented in a totally different format, using only the (often single) confirming positive sample of what may be a much larger outbreak. A recent Parliamentary Question showed no sign that anything was about to change any time soon as to how Defra log the now hundreds of other mammals lost to bTB. This is an indication of a dangerously out of control spillback of this disease in the hands of a government department relying on its own dumbed down figures to justify its continuing inertia..
The body that oversees diseases such as TB is also out of touch with today’s risks. HPA's textbooks are stuck in the groove of exposure to TB in the early part of last century and they have not caught up with 'bovine' TB affecting companion mammals and domestic pets and thus putting their owners’ health at grave risk. Public Health officials continue to play this down but are basing their assumptions on past opportunities for transmission. Few cases are strain typed, but of those that are, official figures for bTB (m.bovis) in humans show 532 cases 1996 – 2009. As the majority of cases will initially be logged as 'm.tuberculosis complex' rather than isolated to m.bovis, this is likely to be an underestimate. Nurses and consultants working with TB patients confirm that the drug regime for the treatment of m.bovis is different and will need to be upgraded from the original m.tuberculosis regime. The original data log however, may not be altered. And liaison with VLA who strain type possible TB patients, is as rare as hens’ teeth.
HPA still quantify 'risk' to bTB by exposure to 'unpasteurised milk, foreign travel and inhabiting homeless shelters'. But exposure to the increasing amount of bacteria from ‘environmental’ sources is an unknown quantity. Neither Dianne Summers nor her alpacas have been exposed to any of HPA's ‘risk’ opportunities, but the alpacas area dead and Dianne has bTB.
Tuberculosis is a slow burn disease, often remaining dormant in unsuspecting and healthy adults for many years. Only when the body is under stress from a second challenge, can lesions break down into full-blown tuberculosis. And that is when this disease becomes a killer. Molecular geneticists say that analysis of recent work suggests that true TB in cattle was eliminated by the 1970s and what we have now, is badger-adapted TB spreading back into the environment. Perhaps mycobacterium meles would be a more accurate label?
Until the early 1980’s, culling of infected badger setts in response to cattle breakdowns continued, but despite the success of such tightly targeted clearances, government policy was progressively sanitised following pressure from animal rights organisations. And since 1997, when a moratorium was imposed on the culling of badgers under section 10 of the Protection of Badgers Act, ‘to prevent the spread of disease’, no action whatsoever has been taken to stop the spread of tuberculosis either within the badger population, and thus to other mammals.
Defra are not killing cattle for the benefit of the farming industry. Neither is this ultimate protection of infected wildlife anything other than a response to lobby cash. Government have a statutory duty to eradicate this disease from both cattle and wildlife under several international directives which protect human health. Killing cattle while leaving a wildlife reservoir to re-infect, is both ineffective and expensive. Sentinel cattle herd breakdowns have mushroomed from their original hotspots two decades ago, to affect up to a third of herds in much of SW England, Wales and the west Midlands. This shows a thoroughly reckless exposure to ‘environmental’ sources of bTB.
‘Bovine’ tuberculosis is not a disease of cattle; it affects many mammals and human beings. It is a zoonosis – that’s what they do. But government inertia will ensure that this ancient and deadly disease, which should have been consigned to history books, will in future affect a wide range of species – including human beings. Dianne Summers is not the first to be affected and she will not be the last.
Short overviews written by Dianne Summers, Dr.Gina Bromage and Mike Birch can now be found on their website at: http://www.alpacatb.com/news.html