for the design of control programs; in extreme cases (as dis- cussed
below, by Fine et al., this volume, and elsewhere) it can happen that
immunization programs, although they protect vaccinated individuals,
actually increase the overall incidence of a particular disease. The
possibility that many nonhuman animal populations may be regulated by
parasitic infections is another topic where it may be argued that
conventional disciplinary boundaries have retarded investigation. While
much ecological research has been devoted to exploring the extent to
which competition or predator-prey interactions may regulate natural
populations or set their patterns of geographical distribution, few
substan- tial studies have considered the possibility that infectious
diseases may serve as regulatory agents (1,8). On the other hand, the
many careful epidemiological studies of the trans- mission and
maintenance of parasitic infections in human and other animal
populations usually assume the host population density to be set by
other considerations, and not dynamically engaged with the disease (see,
for example, (1,2)). With all these considerations in mind, the Dahlem
Workshop from which this book derives aimed to weave strands together --
testing theoretical analysis against empirical facts and patterns, and
identifying outstanding problems -- in pursuit of a better un-
derstanding of the overall population biology of parasitic in- fections.
For the purpose of the workshop, the term "parasite" was de- fined
widely to include viruses, bacteria, protozoans, fungi, and helminths.