RNA viruses are ubiquitous intracellular parasites responsible for many infectious diseases of humans. This is most publicly visible with the AIDS viruses, HIV-1 and HIV-2, which currently infect some 36 million people worldwide, including more than 30% of the adult population in parts of sub-Saharan Africa (Piot et al. 2001), and hepatitis C virus (HCV) which has ∼175 million sufferers globally, many of whom will go on to develop serious liver diseases (WHO 1997). To these ailments can be added myriad other infections, from the benign to the lethal, including many that seem to have appeared only recently. Given the pace at which human ecology is changing, it is evident that more such “emerging diseases” will arise in the future, both in humans and wildlife species (Daszak et al. 2000, Morse 1994).
The success of RNA viruses may in large part be due to their remarkable genetic flexibility. In contrast to DNA-based life forms, the evolution of RNA viruses is fueled by extremely rapid rates of mutation, with around one error occurring during each round of genome replication (Drake and Holland 1999).