On March 20, 1996, the British government confirmed for the first time a probable link between the bovine spongiform encephalopathy (BSE) epidemic and the appearance of a new variant of Creutzfeldt-Jakob disease (nvCJD).
A political scandal
The discovery of a probable connection between the two diseases was a first-rate scandal. After all, it was more than a decade after the first description of BSE and countless insurance policies on the part of the government that meat consumption was safe. From a purely scientific point of view, however, this connection was still controversial at the time: due to the small number of cases, the epidemiological data were still to be assessed as unsafe and experimental data from animal experiments that confirmed the transferability of BSE to other species were not published until September 1997.
The first BSE cases
Let’s start at the beginning: The first confirmed BSE case occurred in Great Britain in 1986, theories about the origin of the disease are still largely speculative. The affected cattle are victims of progressive and always fatal brain and spinal cord degeneration. Over time, these take on the eponymous spongy, perforated structure due to the necrosis / apoptosis of nerve cells. In the 15 years after the first appearance of BSE, over 180,000 cattle were diagnosed with BSE, over 95% of them in the UK. Estimates of the total number of sick cattle range from 400,000 to one million cases. In the early stages, the BSE crisis was just a problem for the agricultural and meat industries, which had to take measures to contain the animal disease. Whole cattle populations have been culled and the use of animal meal as feed, the main way of spreading BSE, has been banned.
The new variant of Creutzfeldt-Jacob disease
However, with the appearance of several dozen cases of a new variant of Creutzfeldt-Jacob disease in 1995, the crisis worsened enormously. The symptoms and prognosis of nvCJD in humans are almost identical to those of BSE and many feared an epidemic of Creutzfeldt-Jakob disease, comparable to the BSE epidemic. Ultimately, the concerns were largely unfounded and more of a cause of media alarmism: instead of several 100,000 cases like BSE, there were fewer than 250 worldwide.
The relationship between BSE and CJD
The broad scientific consensus is that both diseases, BSE and CJD, are triggered by infectious proteins called prions. As early as the 1960s, Tikvah Alper and John Stanley Griffith suspected that some pathogens consisted only of proteins. This resulted from a series of observations: The triggers of scrapie and chronic wasting disease were resistant to high doses of radioactive radiation and could therefore not contain any nucleic acids. In addition, their investigations showed that the infectious agent was significantly smaller than viruses. The American neurologist Stanley B. Prusiner continued Alpers and Griffiths work and in 1982 he announced the discovery of the prion protein. In its functional isoform PrPc, which is mainly alpha-helical in structure, the prion protein is found in various mammalian tissues and is probably involved in cell-cell adhesion and intracellular signaling. The incorrectly folded infectious isoform PrPSc, on the other hand, has a higher proportion of beta-sheet structures and is resistant to proteases. The key difference, however, is that PrPSc is able to change the conformation of correctly folded PrPc to PrPSc. This inevitably leads to the initially slow but exponentially accelerating accumulation of amyloid PrPSc plaques in nerve tissue, neuronal death and ultimately death.
Thanks to improved quality control and, above all, strict regulations and bans related to the use of animal meal as feed, the number of BSE cases per year was reduced to single digits. Nevertheless, transmissible spongiform encephalopathides (TSE) remain a relevant research field with great potential. The standard detection method for PrPSc is still immunohistochemical examination of the brain post mortem. This is obviously a bit too late, but new SOFIA (Surround Optical Fiber Immunoassay) based methods promise reliable prion detection in vivo. Even today, the prognosis for TSE patients is very poor, since all the treatment approaches tested have so far proven to be ineffective.