Disease Monitoring for the
Conservation of Terrestrial Animals
William B. Karesh
Terrestrial environments have undergone unprecedented change over the last century, and many environments no longer resemble the ecosystems within which indigenous animals have evolved. Host—pathogen relationships have been altered, traditional sources of food have been lost, novel pathogens and toxins have been introduced, and novel forms of stress are now present from changes in land-use patterns and associated human activities. Although human impacts have occurred in all ecosystems, their effects have been greatest on terrestrial animals that directly compete with mankind for habitat. The genetic composition of many terrestrial species has also been altered, directly or indirectly, through human actions that have reduced population size or restricted gene flow between populations. Together, these genetic and environmental changes have the potential to dramatically alter the ecology of diseases in terrestrial ecosystems and the overall health of wildlife populations.
Conserving the health of terrestrial animal populations is now an integral part of the greater goal of conserving ecosystem health. Viable animal populations are essential for balanced ecosystems, and healthy, reproductively normal animals are required to maintain this population viability. How environmental changes over the last 10 decades have affected the health of terrestrial wild animals is largely unknown, because information is lacking on what diseases were present in these environments prior to these changes. Whether disease contributed to historic population declines in wild animals was rarely documented, and proof was limited by the diagnostic capabilities available at the time. It is possible that the current perceptions of “emerging diseases” only reflect our ignorance of previous epidemics. Of more concern is the possibility that new diseases are arising or old