Infectious diseases and conservation biology

SUMMARY: Infectious diseases present a special challenge to conservation biologists: they form a largely unexplored component of biodiversity that from one perspective helps promote coexistence and diversity; at the other extreme, there are several examples of pathogens contributing to the extinction of threatened and endangered species. This working group will examine three topics that are central to our understanding of the role pathogens play in conservation biology. Central to the theme of the workshop is the development of a quantitative understanding of how pathogens effect the dynamics of communities that contain more than one potential hosts species. Here we will primarily be concerned with developing empirical and theoretical analysis that examine the role that pathogens play in mediating the coexistence of potentially competing species (or in maintaining genetic diversity within a single host species). We will then examine whether the diversity of host species tends to either buffer, or amplify, disease outbreaks. In particular, we will explore the ecological interactions between transmission route, host diversity and pathogen persistence. This section of the working group will examine empirical data for a number of systems in which we can dissect the relative roles played by host abundance, host resource utilization and host spatial distribution in determining rates of intra- and inter-specific transmission. In conjunction with these largely deterministic and analytical exercises, we shall also examine data for epidemic outbreaks in small (endangered) populations. These analysis will allow us to develop stochastic models that determine the impact of pathogens on populations that are too small to sustain a long-term persistent source of infection. In particular, we will focus on examining the costs and benefits of intervention to prevent further spread of the disease, particularly in the limiting case where small host population size always leads to the pathogens eventual extinction. PROBLEM STATEMENT: Pathogens and infectious diseases create special problems for both the protection of endangered species and for the maintenance of biodiversity. There are several examples of cases where the introduction of a pathogen has produced a significant further decline in the numbers of an already threatened species (black-footed ferrets, hunting dogs in Serengeti, endemic Hawaiian birds). In all of these examples the pathogens involved were ones that utilize common or domestic species as reservoir hosts. There is increasing evidence that species diversity per se may provide an important buffer that minimizes the impact of a pathogen on any individual host species pathogens. Paradoxically pathogens may also play a role in both maintaining biodiversity and in driving processes that lead to increases in local diversity (refs). This workgroup will focus on examining these problems by examining seven different ecological communities for which significant volumes of epidemiological data are also available. Each of the data sets provide important insights into at least one of our main research questions, but we do not expect to apply all of the questions to each of the data sets. We are interested in addressing three general classes of questions: 1) What are the dynamics of a recently introduced pathogen in a small population? In particular, how do deterministic and stochastic factors interact to determine the persistence and extinction of pathogens in small populations? In conjunction with this we will also examine how different types of pathogens contribute to further declines in the abundance of potentially endangered host species? 2) In pathogens that utilize a range of host species, what roles do relative abundance, susceptibility, and overlap in spatial distribution play in determining interspecific rates of pathogen transmission? In particular, how much does ecological information on the behavior and spatial distribution of potential host species complement aetiological information and allow us to identify species that are most likely to act as reservoir hosts for pathogens that provide a significant threat to rare or endangered species? 3) Does the diversity of species used by a pathogen tend to buffer or increase either its persistence or rate of spread? Under what conditions will a pathogen enhance the diversity of species that co-exist in any community? Data sets that will, or potentially could, be used are: Question 1 (1) long term data sets on carnivores, ungulates and their pathogens in the Serengeti; (2) data for a measles outbreak in mountain gorillas in Rwanda; (3) data for avian malaria in introduced and native bird species in Hawaii; Questions 2 & 3 (4) data for the ticks, deer mice, white-tailed deer and Lyme disease in New England; (5) data for ticks, Louping ill, grouse, sheep, blue hares and deer in Scotland; (6) data for racoon rabies in the eastern United States (7) data for duck plague from the National Center for Wildlife Diseases Initially we shall use data sets 1-3 to address question 1. Data sets 4-7 will be used to examine questions 2 & 3. In each case we will examine empirical data for the dynamics of a specific pathogen, this will be used as the basis for first constructing fairly general ecological-epidemiological models. These will then be parameterized using the available empirical data. A variety of analysis will then be undertaken then examine sensitivity of the model to parameterization, initial conditions, and the presence of alternate hosts. We will also examine the consequences of modifying the transmission terms of the models in an attempt to examine how different methods of transmission might modify our conclusions. An important additional exercise will be the development of some stochastic simulation models for pathogens in small populations. These shall be used to examine whether intervention is likely to have a significant impact, and how rapidly it needs to be applied in order to have an effect. This exercise will provide an important set of guidelines for veterinary workers and conservation biologists who frequently disagree on the relative value of disease intervention when dealing with endangered species. The main results of the workshop will be presented in a series of scientific papers which will provide a better understanding of three crucial problems in ecological epidemiology as applied to the management and conservation of endangered species. The first set of these papers will explore the dynamics of infectious diseases in small populations. The second will provide a deeper understanding of the role that ecological interactions play in mediating interspecific diseases transmission. While the third set will develop an understanidng of the role that biodiversity plays in buffering disease outbreaks for some pathogens. The beneficiaries of this will obviously be the participants in the workshop, but we expect the additional 'community benefits' to extend well beyond the marginal boosting of citation indices. There is a considerable need in both the wildlife veterinarian and conservation biology community for a coherent body of work that explains with specific examples the twin role that pathogens play threat and mediator of biodiversity. Thus we can expect the work we produce to be used not only for teaching purposes, but also in helping inform government agencies, and NGO's about how best to respond to parasites and infectious diseases in natural ecological communities. If we examine examples of the recent responses of NGO's and government agencies to challenges presented by infectious diseases, we tend to find that ignorance has led to either extreme and irrational control measures or hard to substantiate 'ad-hoc' measures. (Examples - bison and brucellosis, toxin in Monk seals, malaria in Hawaii). The least we can hope for from our workshop is to firmly refute the commonly held opinion that disease outbreaks are chance random events. If fairly lucky we should be able to provide a set of examples that illustrate the underlying deterministic nature of the ecology of infectious diseases, while also illustrating the crucial, and not entirely random, role that stochastic forces play. Ultimately, this will lead to the development of more rational policies for the management of pathogens in ecological communities.