The persistence of foot-and-mouth disease virus on wool

Five Suffolk sheep, held in a high-security isolation room, were exposed for 2 hours to the aerosol of 3 mature pigs that had been infected with foot-and-mouth disease virus (FMDV), strain O-1-BFS. The fleeces of 3 of the sheep were contaminated with FMDV at 2 days post exposure (dpe), while at 5 dpe the fleeces of all 5 sheep were more extensively, and more heavily, contaminated. The persistence of FMDV on contaminated wool was examined in vitro using multiple 0.5 g samples of Merino wool that were each contaminated with one of 3 strains of FMDV in tissue-culture medium: O-1-BFS, O-Morocco (O-MOR 9/91) or an Asia 1 strain (TAI 1/90). Wool samples were held at either 4 degrees C, 18 degrees C or 37 degrees C, and decay curves were established for each virus at each temperature. These curves predicted that O-1-BFS, O-MOR 9/91 and TAI 1/90 would fall below detectable levels at 72, 70 and 48 days post contamination (pc), respectively, for wool stored at 4 degrees C; at 11, 12 and 12 days pc, respectively, for wool stored at 18 degrees C; and at 57, 68 and 33 hours pc, respectively, for wool stored at 37 degrees C. For wool contaminated with O-1-BFS-infected sheep faeces, urine or blood, or with O-1-BFS-infected cattle saliva, decay curves predicted virus to persist for 5 to 11 days pc at 18 degrees C. We demonstrated that the simulated scouring of FMDV-contaminated wool at 60 degrees to 70 degrees C would usually reduce virus to below detectable levels. The detergent component of the scouring process had little, if any, antiviral activity, and scouring at 20 degrees C or 50 degrees C had limited impact on FMDV titres. We recommend that either (1) simple storage of FMDV-contaminated wool for 4 weeks at temperatures of 18 degrees C or higher, or (2) scouring of contaminated wool at 60 degrees to 70 degrees C would be sufficient to remove the threat of FMDV-contaminated wool being infectious to other animals.