It is a truism among biologists that an organism's phenotype is the
product of both its genotype and its environment. An organism's genotype
contains the total informational potential of the individual, while its
environment shapes the expression of the ge- type, influences the rate
of mutation and occurrence of modifications, and ultimately determines
the likelihood that the genotype (or fractions thereof) will survive
into the next generation. In the relationship between host and pathogen,
therefore, each forms a part of the environment of the other, mutually
influencing the biology of both partners on scales ranging from the life
history of individuals to the fate of populations or entire species.
Molecular biologists working on problems in pathogenesis generally think
of the host organism as the pathogen's environment and perhaps
occasionally consider the pathogen as part of the host's environment.
However, because "environment" can be defined at many scales, so, too,
can phenotypes: if a pathogen, as a species, is c- sidered to exist in a
host, as a species, then among its phenotypes is the nature of the
pandemic disease it can cause within the host community. The
contributors to the proceedings of this NATO Advanced Research Workshop
have treated the interplay of environment and genotype in the
host-pathogen relationship and its relationship to the problem of
emerging infectious disease at both the macroscopic and microscopic/
molecular levels along this continuum of scale (with some human history
thrown in at times for good measure).