of these agents can be considered as emergent, many people from this community have not actively embraced the emerging disease concept.

Responsibility for some other zoonotic infectious agents has largely been in the hands of people associated with public health. These agents include rabies virus; numerous arthropodborne viruses, bacteria, and protozoa; several rodentborne viruses and bacteria; and primateborne pathogens. Obviously, quite a few of these agents are emergent and, under the emerging disease concept, much progress has been made. The cap on progress lies primarily in priority and funding decisions made high in the nation’s public health bureaucracy.

There also are zoonotic infectious agents that seemingly have always been “in between,” and these have often been the subject of foolish turf wars between government officials from the animal health and public health communities. These agents include new influenza viruses; Salmonella enteriditis; Listeria monocytogenes; and, most recently, the West Nile virus. Some progress is being made here, but usually only after contentious turf battles and other delays.

So, the concept of new and emerging zoonotic diseases has not been fully exploited in any of the communities dealing with zoonoses. This situation seems especially appalling given the fact that nearly all emergent disease episodes of the past 10 years have involved zoonotic infectious agents. These agents have included some that maintain an ongoing reservoir life cycle in animals or arthropods, without the permanent establishment of a new life cycle in humans, as well as some “species jumpers” that derive from an ancient reservoir life cycle in animals but have subsequently established a new life cycle in humans that no longer involves an animal reservoir. Given their troubling history, merely having to ask the question “Into which camp will the next important emergent zoonotic agent fall?” suggests that something is wrong.

Determinants in the Emergence of Zoonotic Disease Agents

Many different determinants contribute to the emergence of new zoonotic disease agents. Rarely do such determinants act alone. Given the complexity of their interactions, there likely is no way to predict when or where the next important new zoonotic pathogen will emerge. Consider zoonotic viruses. It has become fashionable to build so-called “predictive” models—this has been done for influenza viruses, for example—but it is likely that the next virus to emerge, influenza or otherwise, will not be as predicted. A danger, of course, is that in our enthusiasm for modeling, we may not recognize the significance of an emergence that does not match up with a favorite model. There also is a danger that too many researchers will



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