spread of lethal brain diseaes
Research by scientists in Japan and at Yale's School of Medicine offer insights into both the spread of and defense against such lethal brain illnesses as Mad Cow Disease, sheep scrapie and Creutzfeldt-Jakob disease (CJD).
The investigators report in the journal Science that infection with a weak strain of CJD in mice prevents infection by more virulent strains -- a finding that has implications for transmission of these diseases from animals to humans.
They also discovered that this protection occurs despite the absence of misfolded proteins known as prions, believed by many scientists to be the cause of the disease -- suggesting there might be another source for the infections.
Mad Cow Disease, sheep scrapie and CJD have been in recent news because of their devastating effects on the brain and concern about transmission of the infectious agents.
In prior research on animals, scientists found a weaker strain of CJD protected against a more destructive strain. This latest study duplicated and extended results of those experiments using a neural cell culture assay.
"We demonstrate a new and very sensitive assay for infection by these agents that can discriminate among different strains, such as those that cause sheep scrapie and human CJD," says senior author Laura Manuelidis, professor and section chief of surgery/neuropathology at Yale.
These studies showed that a persistent protective CJD infection did not require cells from the immune system or misfolded prions. Cells infected with a weak strain of CJD were also protected from infection by two strains of sheep scrapie agent.
The fact that a weak animal agent can protect against a virulent form of the disease in humans may account for the low incidence of CJD linked to Mad Cow Disease in people, says Manuelidis, adding, "Our plan is to use these rapid infectivity assays to identify the different agents -- including those linked to Mad Cow Disease -- on the molecular as well as biological levels."
"This, as well as our previous results showing that most of the abnormal prion protein can be separated from infectious particles, points to a virus as the causal agent," says Manuelidis. "These results are not consistent with the idea that abnormal forms of the prion protein are infectious."
Co-authors on the paper are Yale visiting professor Noriuki Nishida of Gifu University and Sherigeru Katamine of the Nagasaki University Graduate School of Medicine in Japan. The research was funded by the National Institute of Neurological Disorders and Stroke and the Department of Defense National Prion Research Program.
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