Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/1998
Publication Date: N/A
Citation: Interpretive Summary: One of the hallmarks of scrapie, and other related spongiform diseases such as bovine spongiform encephalopathy (mad cow disease), is the presence of clear areas (holes or vacuolations) in brain cells (neurons). During a 2-year period (1995-1997) such vacuoles were detected in neurons of 42% of raccoons in Oregon. Age or sex predisposition was not apparent. Twenty of fthese raccoons were from within a radius of 25 miles of Corvallis in western Oregon. Laboratory tests confirmed that the affected raccoons were negative for rabies and diseases such as scrapie. Electron microscopic examination of the brain revealed accumulation of lipid (fat) within the affected brain cells. These lesions indicate that the affected raccoons had a non-infectious condition. We suspect, but do not have difinitive evidence that their condition is a lipid storage disease caused by a nutritional factor. Further research is required to identify the composition of the intracellular lipid material, to elucidate the mechanism of neuronal vacuolation in raccoons, and to understand the basis for the apparent geographic restrictions of this lesion. Current results will be beneficial to researchers in order to permit differentiation of the disease in raccoons from the transmissible spongiform encephalopathies such as mad cow disease that may be transmissible to humans.
Technical Abstract: During a 2-year period (1995-1997) vacuoles were detected in neurons of 21/50 (42% prevalence) raccoons (Procyon lotor) in Oregon. Age or sex predisposition was not apparent. Twenty of these raccoons were from within a radius of 25 miles of Corvallis in Western Oregon. Microscopically the vacuoles were variable in size, were in the perikarya, and were consistently present in pontine nuclei. Brain tissues were negative for rabies virus antigen by fluorescent antibody test and for the protease- resistant protein (PrP) prion by immunohistochemistry. Electron microscopic examination of the brainstem of selected cases revealed accumulation of electron dense material within neuronal perikarya. Based on light and electron microscopic findings, the accumulated intracellular material appeared to have a high lipid content. These lesions indicate a form of neuronal storage condition. Further research is required to identify the composition of the intracellular lipid material, to elucidate the mechanism of neuronal vacuolation in raccoons, and to understand the basis for the apparent geographic restriction of this lesion.