April, 1999

Scrapie, a fatal brain disease in sheep and goats, has been known for 200 years, but it wasn't until the mid-1980s that it was alleged that this and certain other fatal diseases of the brain are caused by an infectious protein (prion) as opposed to a virus or bacterium. Mad cow disease, which peaked in 1992-93 in Great Britain, has caused the most concern in recent years. The most common prion disorder in humans is Creutzfeld-Jakob disease, although some researchers suspect that Alzheimer's disease may be a similar disorder. Prion diseases all have incubation periods of months to years, and all lead to death over a period of months. Early symptoms vary from fatigue and sleep disorders to aphasia and muscle wasting. The latter might be misdiagnosed as the result of a cerebrovascular event.

For medical and laboratory personnel, it is important to know that the prions in primate tissue are difficult to inactivate and cannot be inactivated by the usual methods of sterilization. Prions can be transmitted through contact with cerebrospinal fluid, brain, and possibly other neurological tissue of contaminated primates and possibly by transmission through contaminated neurosurgical instruments in laboratories, where they have been found to linger for as long as two years. Also, prions can survive for weeks deep in the brains of cadavers in spite of embalming.

Although much is yet to be learned about the transmission of and protection against prion diseases, persons performing biopsies, autopsies, transplantation procedures, dissections, and handling spinal fluids, brain tissue, or contaminated instruments need to follow universal precautions as well as added precautions. Cerebrospinal fluid should be obtained carefully, using double gloves and protective glasses. Biopsies, autopsies, dissections, and handling tissues require use of safety gloves, disposable aprons, and eye and mouth coverings. Instruments should be disposable or decontaminated by soaking in 1N NaOH (40 g/liter) or undiluted NaOH for one hour and then autoclaving at 134°C for one hour. Tissue should be blocked thinly for analysis and soaked in concentrated formic acid for one hour and then four percent formaldehyde solution for at least 48 hours. Existing formalin-fixed tissue in paraffin and stored at room temperature may be infectious for years and should be handled cautiously. Anyone receiving a needlestick or cut should follow the usual procedure of forcing copious bleeding followed by washing vigorously with soap and water.