The agent that causes mad cow disease, scrapie and chronic wasting disease in deer and elk may sometimes be spread through urine, Swiss researchers reported Thursday.
They found that, under certain conditions in mice, the deformed brain proteins known as prions that transmit the disease could be found in urine.
“We tested whether chronic inflammatory kidney disorders would trigger excretion of prion infectivity into urine,” Adriano Aguzzi of the University Hospital of Zurich and colleagues wrote in their report, published in the journal Science.
Scrapie-infected mice with kidney inflammation excreted prions in their urine, and these prions infected other mice with scrapie when injected, Aguzzi and colleagues found.
It is a long way from this laboratory experiment to a real-world setting in which grazing or browsing animals pick up and become infected with urine from others, but the researchers say it shows such transmission is theoretically possible.
Aguzzi, an expert in prion diseases, and his colleagues said the finding could help explain how wild deer and elk in western U.S. states and elsewhere are becoming infected with chronic wasting disease.
It might also explain how scrapie is spread among sheep.
These diseases, known as transmissible spongiform encephalopathies, or TSEs, include bovine spongiform encephalopathy (BSE or mad cow disease), scrapie and, in humans, Creutzfeldt-Jakob disease or CJD.
The diseases are caused by a deformed version of a brain protein called a prion, which is harder to destroy than a virus or bacteria and can spread from animal to animal.
Scrapie has existed for hundreds of years in sheep and was never known to infect another species. In the 1980s, BSE broke out among British cattle and was eventually traced to feed that may have contained the remains of scrapie-infected sheep.
Later, people who ate beef began to develop a version of CJD that has been linked to BSE-infected meat. Called nvCJD, it is different from ordinary CJD and has killed 151 people in Britain so far and a handful in other countries.
Normally, CJD, which has no known cause and no cure, affects about one in a million people globally.
All the diseases gradually destroy the brain and cause death. There is no treatment.
Agriculture officials around the world have changed the rules on animal feed, but cases of BSE still occur on occasion, causing panic among cattle traders and sometimes disrupting the cattle products trade.
Cosmetics and pharmaceuticals made using beef products are now checked for components that could transmit the prions, including brain, nerve matter, spleen and other organs. The researchers suggest that urine might be added to the list of watched-for products.
Aguzzi’s team said the mouse urine did not contain prions when they did not have kidney inflammation. But they said inflammatory kidney conditions caused by bacteria, viruses or autoimmune diseases are common and noted that they can also be associated with advanced dementia -- a symptom of CJD.
They also said one team has reported finding prions in the urine of a CJD patient and another team infected mice with CJD by injecting them with urine from one CJD patient.