Do prions pose a risk in the management of biosolids?

Prions are small folded protein molecules containing no genetic information, which are made up of amino acids, the essential building blocks of all proteins. Prion-like proteins that are found naturally in many (perhaps all) plants and animals are folded differently than normal proteins due to slight amino acid changes in certain regions of the protein. The term prion is often used to refer to such abnormally folded proteins (also referred to as proteinaceous infectious particles), when they have the ability to affect other proteins, causing them to change from the normal form to the abnormal form.

In their normal, non-infectious state, prions are believed to be involved in cell-to-cell communications and other important cell functions. In their abnormal form prions have been linked to the transmission of Bovine Spongiform Encephalitis (BSE, or so-called �Mad Cow’ disease) and Creutzfeld-Jakob Disease (CJD) and variant CJD. There has been discussion about the potential for prions to enter wastewater streams through the discharge of animal waste from abattoirs and similar facilities and thereby passed on to humans through either contact with treated wastewater or biosolids.

The US Water Environment Federation (WEF) reports the following in its Prion Fact Sheet:

“Based on a review of available information and assessments made to date (including a quantitative risk assessment for BSE in biosolids by Gale & Stanfield in the U.K.), it is unlikely that significant levels of prions enter the wastewater collection system and the risk of prion transmission directly to animals and indirectly to humans from biosolids management and effluent land application is extremely low (i.e., practically zero). Prion transmission via biosolids land application seems less likely than other potential food chain pathways.”

A copy of the Fact Sheet can be found here.