Sera collected at euthanasia were gamma-irradiated to inactivate virus. Sera were serially-doubly diluted in a 96 well plate (final volume 50ul/well) to which 200 TCID 50 HeV was added and incubated for 1 hr at 37uC. Following incubation, 2x10 4 Vero cells/well were added and the assay read after 3 days incubation at 37uC with 5% CO 2 .