Mad cow disease almost certainly resulted from the feeding of cattle scrapie-infected sheep carcass protein as dietary supplement. It was first recognized in the UK in 1985, and quickly exploded into an epidemic that has killed over 180,000 cows in the 15 years since it began. However, because of a 1987 prohibition on recycling cattle carcass products as dietary supplements in cattle nutrition, the epidemic gradually subsided, and this year has for the first time declined to a level under 1000 affected cattle during a 12 month period.
Unfortunately, during the 1980's, when BSE was 'incubating' in thousands of cattle (even after it had been recognized), the UK exported thousands of tons of cattle carcass protein dietary supplement to most countries in Europe, as well as to a number of non-European countries, including Japan. This feed supplement has produced outbreaks of BSE all over Europe, particularly in the Republic of Ireland, France, Portugal, and Switzerland, and cases have now also been identified in Germany, the Low Countries, Spain, Italy, Slovakia, and, very recently, in Sweden and Japan. The extent of these outbreaks will to in large measure depend on whether or not these countries have in turn recycled their unsuspected infected cattle carcasses to feed their own cattle populations. Most have done so in the past, but have now, like the UK, prohibited the practice. Because of this and other precautions, it seems unlikely that epidemic BSE in thee countries will achieve anything like the magnitude it did in the UK, and unless the disease is capable of spreading form cow to cow (which is not known to occur), BSE should disappear from the face of the earth within the next few years.
The US escaped harm because we are virtually self-sufficient with respect to carcass-derived dietary protein, and so imported only a single small shipment form the UK before 1989, when our import ban was enacted. If this feed had been contaminated, we would already have seen an outbreak, because the 'incubation period' of BSE is about 5 years, and no case of BSE has been discovered in the US at any time during the 15+ years since the feed was imported. Nevertheless, we continue to look for cases, and we continue strict import prohibitions.
The story would sop her but for the fact that BSE managed to cause CJD in some humans who had eaten contaminated beef products. The culprit was what is euphemistically (and Legally) defined as 'mechanically recovered meat' (MRM), which contains many tissues that consumers do not consider to be meat, including spinal cord and its associated nerve ganglia. In affected cattle these tissues are highly infectious, and so any meat product that contained MRM could also have been infectious. Such products include sausages, meat pies, luncheon meats, canned stews, and even pre-cooked hamburger patties. The opportunities for disease transmission to humans were therefore widespread in the UK, and also existed to some extent on other BSE countries. Today, a mass of regulations and precautions in most countries of the world have eliminated any current risk in beef products, even in countries in which new cases of BSE are still being discovered.
As of September 2001, there have been 106 cases in the UK of this 'variant' CJD (vCJD) caused by consumption of tainted beef products, and an additional four cases in France, one case in the Republic of Ireland, and on case in Hong Kong. The Irish and Hong Kong patients had lived for a time in England, and so most probably contracted the disease there; however, none of the French cases had traveled, and so must have become infected in France. So far, vCJD has not been identified in any other countries, but it will no be surprising if in the near future a case occurs on one or another of the countries in which BSE has appeared. Variant CJD may or may note become a serious problem in the UK, but should not become more than a small problem in the rest of Europe, which has seen far less BSE. Where there is no BSE there cannot be vCJD, so that BSE-free countries should never see a case unless it occurs in someone who has resided in the UK (or other BSE country). Neurologists here continue to be on the alert for any suspicious case, especially in military personnel who were based in Europe during the 1980's and early 1990's