Prions, the infective particles behind diseases such as bovine spongiform encephalopathy (BSE), can breach standard sewage treatment methods, new research shows.
The discovery raises the possibility that the rogue proteins, which are infamously hard to detect, can jump one of the most important barriers that safeguard human health.
Prions are abnormally structured proteins that can transform normal proteins into a form that matches their own. They are infectious and cause a range of neurodegenerative diseases including BSE, also called mad cow disease, and its human equivalent, Creutzfeldt-Jakob disease. Prions are very difficult to destroy, remaining intact in the presence of radiation, disinfectants and extreme heat.
Scientists have long wondered whether prions entering sewers from slaughterhouses and meatpacking facilities could survive the processes used in conventional sewage treatment plants, and unfortunately it now appears that they can, although they are still unlikely to turn up in treated tapwater.
Researchers led by Joel Pedersen, of the University of Wisconsin-Madison, collected sewage from the nearby Nine Springs wastewater treatment plant. They tested this sewage for the presence of proteins that could be turned into prions, and the initial results came up negative. They then added prions collected from the brains of infected hamsters.
The team took this contaminated material and ran it through a recreated miniature sewage treatment facility that they constructed in their laboratory.
The treatment process first used aerobic bacteria to digest the contaminated sewage for seven hours, breaking down organic material. The treated wastewater was then separated from sewage sludge, which settled at the bottom of the treatment tank. The sludge was collected and further digested by anaerobic bacteria at 37 °C for 10 days. They then tested the wastewater and sludge generated by the treatment process.