Linking chronic wasting disease to scrapie by comparison of Spiroplasma mirum ribosomal DNA sequences

Abstract

Transmissible spongiform encephalopathies (TSE) are fatal neurodegenerative diseases of man and animals and are transmitted by a filterable pathogen whose identity is currently unresolved. Our data indicates that Spiroplasma, a wall-less bacterium, is involved in the pathogenesis of TSE. We searched for Spiroplasma ribosomal gene sequences in 10 scrapie-infected sheep brains and 10 normal sheep brains, 7 cervid samples infected with chronic wasting disease (CWD), and 7 normal cervid brains. DNA was extracted from these tissue samples and amplified by polymerase chain reaction (PCR) using primers specific for Spiroplasma-specific 16S rDNA. Specificity of the amplicon was determined by Southern blotting and DNA sequence analyses. Spiroplasma 16S rDNA was found in 8 of 10 scrapie-infected sheep brains and 6 of 7 CWD-infected tissue samples. All normal animal brain samples were negative. Spiroplasma 16S rDNA was also found in two human Creutzfeldt-Jakob diseased (CJD) brains but not in two age-matched normal human brains. DNA sequence analyses of the amplified PCR products from human and animal TSE cases revealed greater than 99% nucleotide sequence homology with Spiroplasma mirum. The presence of Spiroplasma DNA in TSE-infected tissues supports our hypothesis that Spiroplasma may be involved in the pathogenesis of these diseases.