Study calls into question prion route for Mad Cow disease infection
A study published in the Journal of Pathology has suggested that the infectious agents for Bovine Spongiform Encephalopathy (BSE) and variant Creutzfeld-Jakob disease (CJD) may not be as well understood as previously thought. Prions (short for proteinaceous infectious particles) are highly unusual infectious particles which do not carry any DNA or RNA, making them entirely distinct from viruses and bacteria. Prions are abnormal protein particles that infect normal protein particles by converting them to the abnormal form. A team led by Stanley Prusiner from the University of San Francisco discovered prions in 1982, winning him the Nobel Prize for medicine in 1997. Current thinking suggests that in diseases such as BSE, CJD or scrapie, the abnormal prions infect the brain of the host, affecting the shape of the brain, significantly affecting its function. The action through which the prions infect other proteins remains unknown. The current study was led by Martin Jeffrey from the UK Veterinary Laboratories Agency (VLA) in Penicuik, Scotland, and involved researchers based at the Norwegian School of Veterinary Science in Oslo, VLA labs in the UK and the Moredun Research Institute, also in Penicuik. It was co-funded under the Commission's Fifth Framework Programme (FP5) and the UK's Department for Environment, food and Rural Affairs (DEFRA) and involved a study of sheep to see what happened to the prion proteins thought to cause scrapie. Researchers believed that prion particles are absorbed by the gut undigested, and then pass into the bloodstream and into lymph tissue called Peyer's patches, where they multiply and then go on to infect the central nervous system. In the controlled study, the team gave sheep either huge doses of infectious brain material, similar quantities of uninfectious brain material, or sugar solution. To their surprise, the team found that the vast majority of deliberately infected sheep did not develop the disease, and that the prions had been digested. However, three sheep did go on to develop scrapie after 30 days, long after the initial infections had gone. The team found that the infectious prions were forming 'fresh' in the Peyer's patches. 'It would be over-interpretation to say we have evidence for another infectious agent,' said Dr Jeffrey. 'But the prion hypothesis is less than satisfactory.' What this research means is that prions are still the most likely candidates as the infectious particles for diseases such as scrapie, but that the process for infection is much less understood than previously thought. Prions appear to be digested in the gut, but perhaps the prions have other means of crossing into the bloodstream.
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