A microtitre technique for the assay of malignant catarrhal fever virus and neutralising antibody.

A microtitre technique for the quantal assay of a cell-free strain of malignant catarrhal fever virus was developed, using serially passaged bovine embryonic kidney cells. End-points were determined after 12 days' incubation and the mean titre recorded for a single virus stock stored at -70 degrees C over a six-month period was 10(5.5) +/- 0.2 (SD). In neutralisation tests serum/virus mixtures were best held at 37 degrees C for 1 h in microtitre trays before the addition of cells; assays were highly reproducible, figures of 10(1.5) +/- 0.2 being obtained for a single reference serum.