WASHINGTON: The deadly Creutzfeldt-Jakob disease-human form of the 'mad cow' disease - may spread through touch, say scientists who found that an abnormal protein linked to the fatal infection can be detected from the skin of patients.
Scientists from National Institutes of Health and Case Western Reserve University in the US have detected abnormal prion protein in the skin of nearly two dozen people who died from Creutzfeldt-Jakob disease (CJD).
The scientists also exposed a dozen healthy mice to skin extracts from two of the CJD patients, and all developed prion disease.
The study, published in the journal Science Translational Medicine, raise questions about the possible transmissibility of prion diseases via medical procedures involving skin, and whether skin samples might be used to detect prion disease.
Researchers from NIH's National Institute of Allergy and Infectious Diseases (NIAID) stress that the prion-seeding potential found in skin tissue is significantly less than what they have found in studies using brain tissue.
CJD is an incurable and ultimately fatal transmissible, neurodegenerative disorder in the family of prion diseases.
Prion diseases originate when normally harmless prion protein molecules become abnormal and gather in clusters and filaments in the human body and brain.
The reasons for this process are not fully understood.
The accumulation of these clusters has been associated with tissue damage that leaves sponge-like holes in the brain.
Human prion diseases include fatal insomnia; kuru; Gerstmann-Straussler-Scheinker syndrome; and variant, familial and sporadic CJD.
Sporadic CJD is the most common human prion disease, affecting about one in one million people annually worldwide.
Other prion diseases include scrapie in sheep; chronic wasting disease in deer, elk and moose; and bovine spongiform encephalopathy, or mad cow disease, in cattle.
Most people associate prion diseases with the brain, although scientists have found abnormal infectious prion protein in other organs, including the spleen, kidney, lungs and liver.
Using a test for prion diseases, scientists analysed skin tissue from 38 patients - 23 who had died from CJD, and 15 who died of other causes.
They also collected brain tissue from the 23 CJD patients and from seven individuals who died of other causes.
The test correctly detected abnormal prion protein in each CJD patient sample tested and in none of the non-CJD group.
The scientists then exposed humanised laboratory mice to either brain or skin extracts from two of the CJD patients.
All 12 mice inoculated with brain tissue developed prion disease, as did all 12 inoculated with skin extracts, though disease in the skin group took about twice as long - roughly 400 days - to develop. The group also reported that brain degeneration in both groups of infected mice was similar.
The study authors say the results should generate discussion about potential surgical instrument contamination and risk associated with procedures involving CJD patients.
"This study used humanised mice with tissue extracts directly inoculated into the brain, so the system was highly primed for infection," said Byron Caughey, NIAID's Rocky Mountain Laboratories (RML).
"There is no evidence that transmission can occur in real-world situations via casual skin contact. However, the results raise transmission questions that warrant further study," said Caughey.
The study also raises the possibility of using skin tissue samples to test for human and animal prion diseases.
The test is widely used with samples of brain and spinal-fluid for the diagnosis of CJD, but such samples are not always available.