[Effects of polyionic compounds in the plaque formation of different strains of foot-and-mouth disease virus (FMDV) in the swine cell line IB-RS-2]. The effects of dithylaminoethyl (DEAE)-dextran (DD) and dextran-sulfate (DS) were studied in some strains of the foot-and-mouth disease virus (FMDV). The strains ASQ-PG, CR and O, large plaque variants in IB-RS-2 cells, when DD or DS were added to the agar overlay, the plaques were inhibited. However, the strains ASQ-Pp and CI, that are small plaque variants in IB-RS-2 cells, when to the agar overlay was added DD the plaques were greatly enhanced while when was added DS the plaques were inhibited.