The findings by researchers at the U.K. Medical Research Council Prion Unit in London suggest other factors besides the level of the infectious proteins characteristic of prion diseases may trigger the lethality of the disease, ScienceNews.org reported Friday.
Scientists say determining what those factors are could yield treatments that may be able to prevent the infectious protein diseases -- including mad cow disease, scrapie in sheep and Creutzfeldt-Jakob disease in people -- from progressing to a fatal stage.
In a study on mice, prions quickly built up in the brain over the course of a month or two, then remained constant for months with no evidence of disease.
"Whatever you do, it sort of stops at that level and remains there for the duration of the infection," researcher John Collinge said.
The lag time between prion buildup and disease suggests infection is a separate process from toxicity, Collinge and his colleagues said, and they speculate some other as-yet-unknown molecule or cellular process might be needed to make the switch between infectious and toxic prions.