Division A X1

All sera are heat-inactivated at 56 °C for 30 minutes before use.

The constant virus-varying serum neutralisation test on microtitre plates employs MDBK or other susceptible cells. The Colorado, Oxford or any other reference strain of the virus is used at 100 TCID50 per 0,025 ml; inactivated undiluted serum samples are mixed with an equal volume (0,025 ml) of virus suspension. The virus/serum mixtures are incubated for 24 hours at 37 °C in the microtitre plates before the MDBK cells are added. Cells are used at a concentration which forms a complete monolayer after 24 hours.

(i) virus infectivity assay, (ii) serum toxicity controls, (iii) uninoculated cell culture controls, (iv) reference antisera.

The results of the neutralisation test and the titre of the virus used in the test are recorded after three to six days incubation at 37 °C. Serum titres are considered negative if there is no neutralisation at a dilution of 1/2 (undiluted serum).