Vetnuus | March 2026 11 Leading Article A deeper mechanistic understanding is essential. Additionally, pathogens play a pivotal role in maintaining both vertebrate and invertebrate biodiversity—aligning with the Janzen-Connell hypothesis [19,20], which underscores the need for a multipathogen approach to this issue. In this light, it becomes crucial to identify the specific conditions and settings where broadscale policies can effectively impact local ecosystems. This study explores how conservation biology can reduce pathogen transmission among wildlife, ultimately lowering spillover risks to humans. Instead of focusing on direct human transmission, which is influenced by socio-economic and behavioural factors beyond this study, we concentrate on enzootic pathogen circulation, the early stage of potential epidemics. Our investigation examines global conservation strategies and their impact on wildlife pathogen transmission, pinpointing critical knowledge gaps for designing strategies with dual benefits for biodiversity and public health. By assessing the risks and rewards of each approach, we identify strategies that offer the safest public health co-benefits while minimising zoonotic risk. Potential Impacts of Landscape Conservation Strategies on Pathogen Transmission — The Role of Pathogen Adaptation and Habitat Connectivity Since early research on the dilution effect [21,22], using conservation biology to reduce the risk of emerging infections has been considered. However, our understanding of the dilution effect, its mechanisms, and applicability was then underdeveloped. Since then, knowledge in conservation biology has significantly grown, highlighting the need to merge these fields. Many reviews have outlined the conditions under which a dilution effect can be observed—such as significant variability in host competence, horizontal transmission, a link between host abundance and competence, and frequency-dependent transmission. Similarly, conservation strategies have been extensively explored, from identifying key species to target, determining the optimal size of protected areas, and ensuring connectivity between habitat patches [23]. Rather than delving into an exhaustive review of this literature here, more detailed discussions are available in the supplementary materials. What remains clear is the pressing need to align these advances in conservation and disease ecology, paving the way for strategies that not only protect biodiversity but also mitigate the risk of pathogen spread. In this study, we focus on the potential effects of concrete conservation strategies on host communities and, consequently, the expected circulation of pathogens within ecosystems (results are summarised in Table 1). To do so, we consider the balance between hazard (pathogen diversity, defined by the number of pathogen species, as a potential source of harm) and risk (actual exposure to a given pathogen through circulation), as described by Hosseini et al. (2017) [24]. Our focus is specifically on landscape selection strategies, particularly the debate over whether a single large reserve or several small reserves (i.e., the SLOSS debate) is more effective. It is important to note that we centre our analysis on pathogens with minimal virulence in their wild hosts. We define here “virulence” as the infection cost for the host, for which a “minimal virulence” has a negligible impact on host abundance. As such, they do not significantly disrupt host community diversity or assembly — to avoid introducing complex host-pathogen dynamics. Additionally, we have chosen to maintain a broad perspective rather than focusing on a single pathogen to keep our findings widely applicable (for specific examples of how conservation strategies affect pathogen transmission, see Lambert et al., 2020) [25]. Conservation Strategies Consequences on Animal Communities Ref Consequences on Pathogens Communities on the Ecosystem A Consequences on Pathogens Communities on the Ecosystem B Several Small Reserves Maximize regional diversity by combining small patches with several different species. Many patches, interconnected,with low species richness in each [26,27] Rapid pathogen adaptation: high pathogen transmission within each reserve, which may lead to different pathogen adaptation within each patch (local speciation). Slow pathogen adaptation: hot and cold spots of transmission and adaptation. Strong genetic drift effects may limit adaptation if interconnectivity between patches is strong. Intermediate Strategy Maximize the time to population extinction Few patches with a reasonably high species richness 28,29] Medium level of transmission. Determining the ideal patch size could be considered by looking at the pathogen communities. Single Large Reserves Larger areas contain more species than smaller areas (species-area relationship theory and equilibrium theory of island biogeography). This decreases the probability of species extinction. Classic Reserves One patch with high species richness [30,31] More pathogens but less transmission (dilution effect) More pathogens species and more transmission (amplification effect) Biodiversity Hotspots One patch with high species richness [32,33] More pathogens but less transmission (dilution effect) More pathogens species and more transmission (amplification effect) Key Biodiversity Areas (KBAs) Case-by-case [34,35] Host communities being heterogeneous between KBAs, it is difficult to extrapolate for pathogen communities Table 1. Summary of different conservation strategies, their impact on animal communities, and their potential impact on pathogen transmission. We assume the conditions necessary for a dilution effect: (1) horizontally transmitted pathogen (i.e., no vertical transmission), and (2) animal communities with a high probability of extinction for low-abundance species. As shown in Figure 1, ecosystem A assumes a perfect positive correlation between competence and species abundance (a perfect context for a dilution effect). Conversely, in ecosystem B, we assume a perfect negative correlation between competence and species abundance (a perfect context for an amplification effect). >>>12
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