Figure 3.

A model for the formation of rare genotypes and novel genoclouds. Rare genotypes arise by a variety of mechanisms, including import of DNA from unrelated bacteria, translocation of opa alleles, and single step mutations. Those variants that affect antigens and result in immune escape will multiply preferentially because of selection pressures by the host immune system. However, many of these variants also result in lessened fitness and are eliminated by competition and bottlenecks during spread from host to host and country to country. On rare occasions, antigenic variants with increased fitness can form new genoclouds and repeat the cycle.