Phasevarions have been identified in several mucosal-associated human-adapted pathogens, which include; Haemophilus influenzae, Neisseria meningitidis, Neisseria gonorrhoeae, Helicobacter pylori, Moraxella catarrhalis, and Streptococcus pneumoniae. All described phasevarions regulate expression of proteins that are involved in host colonization, survival, and pathogenesis, and many regulate putative vaccine targets. The presence of phasevarions complicates identification of stably expressed proteins, as the regulated genes do not contain any identifiable features. The only way to identify genes in a phasevarion is by detailed study of the organisms containing such systems. Study of the phasevarions, and identification of proteins they regulate, is therefore critical to generate effective and stable vaccines.
