Vegetarians not safe from mad cow prions

As if we did not have enough problems: A new study suggests that infectious prions — thought to be the causative agents in mad cow disease and human vCJD — can survive wastewater decontamination and wind up in fertilizer, potentially contaminating fruit and vegetables. The prions would be present in such low quantities that they are unlikely to pose a health threat, but as a precaution, “we should prevent the entry of prions into wastewater treatment plants,” says microbiologist Joel Pedersen, of the University of Wisconsin in Madison, who led the research. Prions could end up in wastewater treatment plants via slaughterhouse drains, hunted game cleaned in a sink, or humans with vCJD shedding prions in their urine or feces, Pedersen says.

NewScientist’s Ewen Callaway writes that previous studies have suggested that prions can survive heat treatment and caustic chemicals, but to see how prions fare during sewage treatment, Pedersen’s team spiked sludge from a local treatment plant with infectious prions, and then subjected the toxic brew to a typical wastewater treatment regimen. This typically involves three weeks of filtration, separation and incubation with microbes that break down contaminants in the sludge, resulting in clean water and “biosolids” free of most human pathogens, which can be used as a fertilizer. When Pedersen’s team tested the sewage soup at various stages, they found the water was clean, but the biosolids were contaminated with prions. “The sludge digestion seems to have no effect on the prion protein,” he says. Prions from culled livestock could also lurk in landfills, says Pederson, whose team is testing whether prions survive in dumps. Recent mad cow disease scares in Britain, Canada, and the United States resulted in culls of thousands of potentially tainted animals, and many ended up underground. Tisha Pettaway, a representative for the US Environmental Protection Agency, which regulates sewage treatment and partially funded the study, says prions pose little threat to the water supply and even less to food. Still, she says “other types of treatment systems, such as those that employ alkaline hydrolysis, ie, addition of lime, would inactivate prions should they get into the system.”