The invention relates to peptides derived from or similar to the E.sup.ms protein of pestiviruses for type-specific diagnosis of infection, for eliciting antibiotic activity, and for transport of substances into a cell. For these purposes, the invention provides, among other things, an isolated, synthetic or recombinant protein or peptide module or functional equivalent thereof comprising an amino acid sequence having significant homology to, for example, an amino acid sequence of a peptide located from about amino acid position (a) 194 to about 220 in a pestiviral E.sup.ms protein (b) 59 to about 88 in an L3 loop of a cytotoxic RNase of a ribosome-inactivating protein, or (c) 187 to about 223 in a respiratory syncytial virus G-protein.