A simple and effective method for inactivating virus infectivity in formalin-fixed tissue samples from patients with Creutzfeldt-Jakob disease.

We fixed brains from hamsters infected with scrapie virus in (1) formalin, (2) phenol-saturated formalin, (3) formalin with a 1-hour immersion in formic acid, or (4) phenol-saturated formalin with a 1-hour immersion in formic acid. In addition, we used the formalin-formic acid procedure on brains from mice infected with the virus of Creutzfeldt-Jakob disease. Formic acid proved superior to phenol in respect to both disinfection and tissue preservation, almost completely eliminating virus infectivity in sections that were histologically indistinguishable from formalin-fixed material. The inclusion of a formic acid step in routine formaldehyde tissue fixation will thus provide histologic sections of excellent quality, and virtually eliminate the risk of handling infectious material in the subsequent neuropathologic processing of tissues from patients with CJD.