BSE: Science & research - TSE Diagnostics - Strain typing
There are different strains of TSE agent which have traditionally been defined by the length of the incubation period and the characteristic pathology seen after serial passaging in mice. A widely-held theory is that “strain types” may represent differences in the conformation of the disease-associated prion protein, which have an effect on the disease characteristics seen in the infected host. The vast majority of BSE cases have consisted of one strain. Scrapie, in contrast, consists of multiple strains. Strains can cross the species barrier e.g. the BSE strain in cattle has the same strain properties in mice as feline spongiform encephalopathy in cats and vCJD in humans.
Understanding the implications for animal and human health of the different strains of TSEs, as well as quickly identifying any new strains with potentially different implications for animal and human health, are important areas of work for Defra.
Strain typing requires cross-disciplinary expertise in pathology, biochemistry and bioassay and uses a variety of research techniques including:
- Mouse bioassays: A key stage in the process of isolating and characterising individual strains by incubation period and examination of the brain after death.
- Examining the pattern of holes (vacuoles) in the brain produced by the disease (histological lesion profiling).
- Testing sections of tissues to look for patterns in the deposits of disease-related PrP, using antibodies (immunohistochemistry).
- Separation of proteins to identify the specific TSE, the conformation of PrPSc in the sample or the affinity to specific antibodies (biochemical and immunoblotting techniques).
A summary of these techniques related to identifying BSE is available from SEAC: Review of BSE strain typing 
(February 2004).
While mouse bioassays provide the standard for strain typing, more rapid biochemical approaches are being examined and used as screening tests.
Key aims of Defra’s work in this area
- To investigate diagnostic procedures that could be used to distinguish BSE from scrapie strains, including atypical scrapie in sheep.
- To investigate the significance of the different strain types.
Overview of research in this area
Examples of current Defra work on strain typing include:
- Studying historical samples to test for new strains of BSE (projects SE1795 and SE1796).
- Biochemical characterisation of UK atypical scrapie cases (project SE1789).
- Developing methods to detect structural differences in the prion protein that are associated with differential cleavage by enzymes (projects SE1760, SE1766, SE1785, SE1792).
- Developing statistical methods to recognise differences between different sheep TSEs after inoculation into mice (projects SE0241, SE0242, SE1779, SE1787, SE1791).
- Correlating the characteristics of strains in mice with biochemical assays to detect PrPSc (project SE1848).
- Investigating panels of antibodies or enzymes that may distinguish between strains of TSEs.
- Cataloguing naturally-occurring scrapie strains (projects SE1919, SE1938, SE1849).
- Developing novel rapid in vitro methods for strain typing (projects SE1700, SE2013).
- Studying how rendering and heat affects different TSE strains (project SE1438).
Page last modified: 18 March, 2008