The isolated case of suspected BSE in a cow on a farm in Co Louth this week doesn't herald a return of the BSE epidemic.
The biggest outbreak in cattle was in the UK where they had almost 180,000 cases, peaking in the 1990s. The inclusion of contaminated meat and bone meal in the cows' rations triggered the disease problem in the UK and resulted in smaller outbreaks in other cattle-producing countries where contaminated meat and bone meal was fed. The epidemic triggered a series of regulatory controls for the cattle and meat industry, which were serially strengthened as more information became available on how the disease behaved.
This is an unusual disease, not caused by a conventional microbe like a bacteria, virus or protozoa. The agent is called a prion protein which can form different shapes. When in its normal shape it is a structural protein in the brains and central nervous systems of all mammals.
Problems arise when it adopts an abnormal shape. It is like if you build a wall with square shaped blocks, you can build a solid structure, but if you were building it with circular, or triangular, blocks there could be holes in the wall. Hence the brain of the affected cows may have holes like a sponge, which is how the full name of BSE, "bovine spongiform encephalopathy", arose. When an animal's nervous tissue encounters the abnormal protein, it causes the normal ones to slowly change shape and eventually disease of the nervous system results.
One of the series of controls introduced by the EU to prevent any possible spread of this disease to humans was to exclude all bovine tissues containing prion proteins from the food chain, and these controls remain in place. The brain and spinal cord are the main tissues that contain the prion proteins.
Ireland's grass-based production system reduced our need to use meat and bone meal, which in part explains why our incidence in cattle did not reach the high levels seen in the UK. In 2002 we had 333 cases, 126 in 2004, 41 in 2006, 23 in 2008, 3 in 2011, 1 in 2013 and none in 2014.
We thought we had BSE eradicated and the global organisation for animal diseases, the OIE, did so also and recently classified our BSE status as 'negligible'. This one case will move our BSE status to the next category, 'controllable'.
One animal identified in a herd of over six million will not lead to over concern in the OIE. Complete eradication of a disease requires a good few years of no cases before one can be confident that the disease is gone forever. The OIE acknowledges that we have good controls in place and the fact that we uncovered this suspect case, and have been open and transparent about it, is a reflection of our approach to tacking the problem.
How this animal may have acquired the disease is now the subject of a detailed investigation by the Department of Agriculture.
What does it all mean for the consumer? There is no reason for alarm, the key controls of exclusion of central nervous system tissue from the food chain continue to exist, and in Ireland all animals are inspected by veterinary surgeons in the lairage of the abattoirs to ensure they are clinically healthy. Only healthy animals are permitted to enter the food chain.
Dr Patrick Wall is a professor of public health in UCD and former chairperson of the European Food Safety Authority