A plaque assay for feline panleukopenia virus

Plaque formation with representative strains of feline panleukopenia virus (FPV) has been obtained using a permanent line of feline kidney cells under agarose overlay. FPV-infected cells appear as white plaques after neutral red staining. Plaque size is determined by the extent of cell division in the infected monolayer. FPV assay by the plaque procedure is rapid and gives infectivity titres which exceed those determined by the common inclusion body and immunofluorescent assays of FPV by a factor of about 100 and 10, respectively. Moreover, the plaque assay offers an effective means for the quantification of neutralizing antibodies in feline sera as well as for the detection of heat-stable substances in bovine sera which strongly interfere with replication of the virus.