Serological Testing

The assays below are used to detect and quantify antibodies against the outer capsid structural proteins that are produced following both vaccination against and infection with foot and mouth disease virus (FMDV).

Protocols for these assays, as undertaken at The Pirbright Institute, are linked in the text and based on those outlined in Chapter 3.1.8. Foot and mouth disease, of the OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals.

The LPBE can be used as either a screening or a quantitative titration assay. As an indirect sandwich ELISA, it is both strain- and serotype-specific, and uses polyclonal antibodies from Guinea pigs and Rabbits. If antibodies are present in the serum, they will block antigen/virus binding to the guinea pig polyclonal antibodies, which will inhibit colour complex formation. If colour development does occur, this indicates that FMDV serotype-specific antibodies are absent in the test sample.LPBE protocol

The VNT assay measures the ability of a serum to neutralise a fixed dose of virus and prevent the appearance of a readily observable cytopathic effect (CPE) in susceptible cells grown in culture. Test parameters are well defined, and it is the "Gold Standard" for detecting antibodies against vesicular viruses including FMDV, SVDV and VSV antibodies.VNT protocol

Vaccine matching analysis can be achieved using either a 2D version of the VNT or a LPBE, although the LPBE is much less flexible, therefore the 2D VNT is often favoured. The 2D VNT characterises the antigenic relationship (using r1-values) between a field isolate and a vaccine strain, in order to estimate antigen/vaccine efficacy during an outbreak of foot-and-mouth disease.

The test calculates the neutralisation titres of the field isolate and the vaccine strain against the homologous vaccine strain’s bovine vaccinal sera. The antigenic relationship between the field virus and the vaccine virus is then defined as the ratio of the neutralising titre of the field virus to that of the vaccine virus. An r1-value ≥0.3 suggests that there is a close antigenic relationship between the field isolate and vaccine strain tested. A potent vaccine containing the vaccine strain is likely to confer protection.2D-VNT protocol

For further information, please contact Anna.Ludi@pirbright.ac.uk

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