The invention is directed to immunogenic compositions and method of treatment comprising a peptide or nucleic acid that encodes the peptide that induces an immune response in a mammal that is protective against infection by one or more pathogens. The peptide sequence contains multiple epitopes, wherein at least one epitope is a composite epitope which is a combination of two or more conserved epitopes of the pathogen wherein the amino acid sequence of the composite is not an amino acid sequence of the pathogen. In addition, the invention is directed to vaccines comprising the peptide or nucleic acid that encodes the peptide for treating and preventing an infection in mammals such as animals and humans.