Recovery and assay of African swine fever and swine vesicular disease viruses from pig slurry

Assaying samples for infectious virus is more difficult when the sample is toxic to cells used in the assay, e.g. with samples of infected pig slurry. Various techniques were compared for the recovery of African swine fever virus (ASFV) and swine vesicular disease virus (SVDV) in pig slurry. Extraction with Freon led to 80-100% recovery of SVDV added to pig slurry. The assay sensitivity enabled undiluted, centrifuged sample to be put directly onto monolayers of IB-RS2 cells, allowing a minimum detection level of 100.7 pfu ml-1. ASFV was difficult to recover intact, and the best technique allowed a recovery of 60% with a minimum detectable level of 101.8 HAD50 ml-1, due to toxicity to the cells at low sample dilutions. Extraction with the addition of an equal volume of ox serum to inoculated slurry was best at recovering ASFV. Poor recoveries with the other techniques may have been due to the inactivation of the virus while in the slurry rather than as a result of the inability of the method to extract ASFV.