Viral evolution and emerging viral infections: what future for the viruses? A theoretical evaluation based on informational spaces and quasispecies.

Emergence of new viruses is dependent on the intrinsic and extrinsic constraints exerting on viral evolution. Intrinsic constraints are semantic and grammatical in nature. They are analysed here in reference to Hamming's spaces, driving to a new interpretation of the evolution of the quasispecies of Manfred Eigen. Extrinsic constraints are relevant to the fact that viral evolution is always a co-evolution story, with two or three partners implicated (the viruses, their hosts and eventually their vectors). They imply that viral phylogenies are disconnected, and viruses constitute a polyphyletic system. A possible consequence is that potential viral families are already known, or at least are present in nature, in such a manner that the frames for future viral evolution are already determined and that the probability for the emergence of a new frame is nil. Nevertheless, the emergence of new pathogens in the existing frames remain possible.