Antibodies to BTV present in the test serum block the reactivity of the monoclonal antibody (Mab) and result in a reduction in the expected colour development after the addition of enzyme labelled anti-mouse antibody, and chromogen/ substrate. Sera can be tested at a single dilution of 1:5 (spot test – Appendix 1) or may be titrated (serum titration – Appendix 2) to give dilution end-point. Inhibition values higher than 50 % may be regarded as positive.
