Two examples of known virulence factors clearly illustrate this.
Analogous examples of immunopathological virulence are found in a huge array of infectious diseases (Graham et al. 2005a).
Examples of increased virulence do also exist, for example, Little et al., [ 40] demonstrated in the D. magna – P. ramosa system that P. ramosa, a burst killer, increased in virulence upon adaptation to a specific host genotype without transmissive stages being present, even though King et al. [ 41] have demonstrated empirically that long lived stage are formed.
Despite the burden of carrying additional genetic material, bacteria can benefit from prophages, for example, in terms of virulence; a well-known example is the cholera toxin [ 19] encoded on the CTXphi phage, which can be integrated into the Vibrio cholera chromosome.
The downgraded translocation efficiency of YopJ may represent an additional example of a virulence mechanism developed by Y. pestis.
One more example of a virulence jump is given by the emergence of a highly pathogenic form of porcine reproductive and respiratory syndrome virus in China in 2006, based on an accumulation of point mutations and deletions.
Strains of T. brucei can vary naturally in a range of different phenotypes, for example, in terms of virulence, growth, drug resistance and resistance to human serum.
For example, a variety of virulence factors that have the potential to cause inflammation are produced by Escherichia coli spp., as well as other members of the Enterobacteriacae [ 34].
There are other examples of atypically virulent strains causing anthrax-like symptoms with plasmid-encoded virulence factors.
The study of pathogenicity has revealed multiple examples of convergently evolved virulence mechanisms.
