Abstract: In a method of identifying novel virulence associated genetic information about a pathogenic microorganism including information about open reading frames (ORFs) having (a) assigned functions, (b) no assigned functions, (c) showing similarity with hypothetical proteins from other species is provided. An obligate human parasite evolutionary deprived of a substantial portion of its coding capacity is selected and genetic information about it is provided. By comparing the genetic information at least one open reading frame (ORF) common to the microorganism and the human parasite is identified, which codes for a protein (c) showing similarity with a hypothetical protein from other microorganism species. By introduction of a mutation in the ORF a mutated ORF is produced. The pathogenicity of the mutated pathogenic organism is assessed and compared with that of the corresponding non-mutated pathogenic organism.

Abstract: Immunogenic compositions containing Francisella components or modified live strains of the Francisella species and their use in preventing or treating disease such as tularemia.