Characteristics of scrapie isolates derived from hay mites

Previous epidemiological evidence suggested that in some instances a vector and/or reservoir is involved in the occurrence and spread of transmissible spongiform encephalopathies (TSEs). In a preliminary study, hay mite prepa rations from five Icelandic farms with a history of scrapie were injected i nto mice, and some of these mice became sick after long incubation periods. To confirm that the disease was scrapie, subsequent passages in mice were performed. In addition, the characteristics of the disease process in these passages were assessed and the results compared to those findings with sta ndard scrapie strains. As expected for scrapie, subsequent passages in the same host led to shortened incubation periods compared to those in primary isolate mice, and all mice had spongiform changes in brain. Results were si milar for three of four isolates with regard to clinical manifestations, th e incubation periods in mice of the three scrapie incubation-period genotyp es (s7s7, s7p7, p7p7), and the PrPSc Western blot (WB) pattern. The charact eristics of the fourth isolate were markedly different from the other three isolates with regard to these parameters. Comparison of the characteristic s of standard mouse-adapted scrapie strains and the four isolates revealed differences; these differences were particularly pronounced for the fourth isolate.