Certain fertility hormones could theoretically put women at risk of developing brain-wasting Creutzfeldt-Jakob disease.

The fatal disease is spread by prions, infectious and misfolded proteins that also cause BSE, commonly known as mad cow disease in cattle. 

In Thursday's issue of the journal Public Library of Science One, researchers from Canada, France and the U.S. show for the first time that prions can exist in fertility hormones derived from urine.

The risk is theoretical and no single case has been documented of a woman contracting CJD from the hormone products, stressed Dr. Daniel Krewski, an author of the study and director of the McLaughlin Centre for Population Health Risk Assessment at the University of Ottawa.

"The risk is likely to be small but it is a risk that could be a real risk and what we're trying to do is perhaps be a little bit more proactive than we've been in the past when we identify a new potential pathway of disease transmission," Krewski said.

Fertility doctors said there is a widely-used alternative to urine-based fertility products. But those synthetic hormones don't work for every woman and some still opt for urine-based treatments.

"I don't use them [urine-derived hormones] very often but the next time the opportunity comes up to, I'll have to have a very careful discussion with my patients so they're fully aware of our now limited understanding of the safety," said Dr. Tom Hannam, who runs a fertility centre in Toronto.

No screening test

About one in 10,000 Canadians is affected by CJD, and could theoretically pass on prion proteins in their urine or blood. Krewski's research used highly sensitive, state-of-the-art testing to detect the proteins in samples of the fertility drugs. 

The researchers said they are flagging the potential danger to look for proactive ways of preventing risks to the population in the future rather than reacting to risks.

For Misty Busch of Cloverdale, B.C., who injected fertility hormones derived from human urine when she was trying to get pregnant with her three-year-old twins, learning of the tiny possibility of prion disease infection was worrying.

There is no commercially available test to screen donors for CJD or to help women like Busch determine if they've been exposed to prions.

"I guess I'm going to have to sit and wait til we've got more technology," Busch said.

Human prion diseases like CJD can also be transmitted through medical or surgical procedures.

Urine donors are screened for symptoms of neurological disease but prion diseases can have a long incubation period during which the urine may be infectious, said study co-author Dr. Neil Cashman, scientific director of PrioNet Canada, and Canada Research Chair in Neurodegeneration and Protein Misfolding Diseases at the University of British Columbia.

With files from CBC's Pauline Dakin