Ten years after the SARS epidemic, zoonotic and emerging viruses have become a growing
field of research. Some remarkable novel virus descriptions in animals have demonstrated
how ignorant we are of the diversity of viruses around us. In our efforts to delineate
viral origins we may have to re-assess our concept of reservoir. In many instances,
we are mixing up ecological and epidemiological implications of viral evolution. Among
the biggest challenges in this field is the integration of the concepts of virus-host
codivergence, and viral host switching. In addition, assessments of viral reservoirs
with the intention to predict future pandemic threats would have to take into account
important host and virus traits which cannot be predicted merely from virus genes.
For example, we need to know whether there are hosts which have a higher propensity
to carry broader spectra or higher concentrations of viruses, potentially without
being affected. Among the viruses borne in such reservoirs, there may be some that
are more promiscuous in their choice of hosts than others, potentially due to the
conservedness of their receptor structures or the way they interfere with conserved-
or not-so-conserved immune properties. A synopsis of available approaches demonstrates
how much work needs to be done before we will be able to assess functional, rather
than genetic diversity of reservoir-borne viruses.
