The host specificity of three species of Bacillus (B. cereus, B. thuringiensis, and B. anthracis) is determined by the presence of virulence plasmids that determine the type of particular virulence factors produced (Gohar et al., 2005). ranges and thereby at least in part dictate the specialization so characteristic of parasitic organisms. Also in support of this claim is that some patterns of parasite host specificity can be attributed to the operation of specific immune evasion strategies, and that such strategies are pervasive among parasites.