Evaluating the Species Barrier

Abstract

A Transmissible Spongiform Encephalopathy (TSE) agent from one species generally transmits poorly to a new species, a phenomenon known as the species barrier. However once in the new species it generally but not always adapts and then more readily transmits within the new host. No single test is available to determine accurately the ability of a prion strain to transmit between species. Evaluating the species barrier for any prion strain has to take into consideration as much information as can be gathered for that strain from surveillance and research. The interactions of the agent with a particular host can be measured by in vivo and in vitro methods and assessing the species barrier needs to make full use of all the tools available. This review will identify the important considerations that need to be made when evaluating the species barrier.

Keywords: PrP; Prion transmission; Species barrier; Transgenic models; Transmissible Spongiform Encephalopathies (TSE).

Fig. 1

Incubation period rankings can be a useful tool in assessing TSE strains. Examples of incubation periods from primary passage of experimental sheep BSE, FSE, BSE, vCJD and scrapie in three lines of wild type mice. Abbreviations: BSE, Bovine Spongiform Encephalopathy; FSE, Feline Spongiform Encephalopathy; vCJD, variant Creutzfeldt-Jakob disease.

Fig. 2

Assessing adaptation of a TSE agent in vivo and in vitro. Serial passage through mice demonstrates higher susceptibilities and strain characteristics can be determined. In vitro assays can give a biochemical assessment of transmission and adaptation.