Pathogens and policy – wildlife management lessons from disease ecology

In recent years, diseases have become increasingly important in the fields of wildlife ecology, management, and conservation. Chronic wasting disease, a fatal prion disease affecting cervids, has long been present in North America but has now also emerged in Norway and South Korea, where wildlife managers are working to contain its spread. African swine fever, a highly lethal viral disease of wild boar and domestic pigs, poses a serious threat to the European pig industry. Meanwhile, the range expansion of ticks, driven in part by climate change, is elevating the risk of Lyme disease and other tick-borne illnesses in wildlife populations as well as in humans. And the amphibian fungal disease, chytridiomycosis, which has caused the extinction of over 90 species and the precipitous decline of 500 others, illustrates the risk that diseases may pose to the persistence of wild populations. Beyond causing population declines in affected wildlife species, diseases have profound effects on ecosystem functioning and also pose significant health and economic risks to both livestock and humans. Despite the growing relevance of wildlife diseases, there remains a lack of practical experience and guidance for their effective management. To address this gap, Wildlife Biology has launched this special issue to help build a scientific foundation for wildlife disease management. This issue complements a recent special issue in our sister journal Ecography, which focused on the science of disease ecology and pathogeography (https://nsojournals.onlinelibrary.wiley.com/toc/16000587/2024/2024/10). In contrast, we emphasize applied perspectives and management-oriented research on wildlife diseases. Understanding how infectious agents interact with wildlife hosts and the environment is essential for effective management. This special issue brings together nine studies that examine ecological, behavioural, and landscape-level factors driving disease dynamics in wild animal populations. The infectious agents covered range from viruses and prions to fungi, protozoa, and helminths, as well as tick-borne agents – yet despite this diversity, each paper offers valuable, applied insights into wildlife health monitoring, population assessments, and disease control strategies. They reveal the profound and often underappreciated role diseases play as integral components of ecological systems, affecting wildlife at every level, from individuals and populations to entire communities. As knowledge of wildlife disease ecology increases, so too does recognition of this field's importance in understanding the impacts disease has on shaping ecological systems, but also for managing the seemingly increasing threat of emerging diseases. We hope this special issue contributes to our understanding that pathogens are a natural force shaping ecological dynamics – one that must be considered in research, management, and policy. The issue opens with investigations of protozoan blood parasites in birds and reptiles, which emphasize host-specific infection patterns with clear implications for wildlife health assessments and demographic monitoring. Marzal et al. (2024) examined the prevalence and impact of Hepatozoon parasites in captive spectacled caimans Caiman crocodilus and American crocodiles Crocodylus acutus, finding that 14% of spectacled caimans – but none of the crocodiles – were infected, with subadults being most affected. Interestingly, infected caimans had better body condition than uninfected ones, suggesting that some behavioural trait by this age class increases transmission risk. These findings offer insights into crocodilian disease ecology with implications for management, including conservation strategies. Rimša et al. (2024) investigated blood parasite infections in a population of common starlings Sturnus vulgaris in Latvia over four breeding seasons, revealing a low to moderate annual prevalence between about 3 and 16% of Haemoproteus, Plasmodium, and Leucocytozoon parasites. Seven parasite lineages were newly identified in this host species, and infections were generally chronic with low parasitism but signs of immune activation, clearly indicating health impairment and reductions in energy levels. Management should focus on mitigating the effects of upcoming additional stressors, like drought events due to climate warming or agricultural intensification. Both these papers highlight the paucity of knowledge regarding the effects of blood parasites on wildlife demography and population dynamics, a critical gap in population management. Turning to helminth infections in ungulates, three papers provide management lessons from Europe and North America. Wild et al. (2024) investigated lung parasite infections in wild roe deer Capreolus capreolus from southern Germany, finding that over half of the individuals were infected, primarily with the lungworms Varestrongylus capreoli and Dictyocaulus capreolus. Infection rates were higher in males and juveniles, and parasitized individuals had significantly lower body weights, indicating that these parasites may negatively affect host condition and, hence, reduce the economic value of deer harvested by hunters. The findings highlight key demographic and environmental factors influencing parasite burden in wild roe deer. Similarly, König and Ehrmantraut (2024) assessed the spread of the invasive American liver fluke Fascioloides magna in ungulates in southern Germany, finding high infection rates in red deer Cervus elaphus (36%) but very low in roe deer (3%) and none in wild boar Sus scrofa. Since the commencement of targeted red deer population reduction measures several years prior, there has been a significant decline in both infection levels and the burden of fluke per liver. However, older deer and proximity to wetlands, where the intermediate snail host occurs, have been identified as persistent risk factors. The findings indicate an urgent need for continued management to prevent widespread transmission among native deer populations. Pouchet et al. (2024) extend this perspective to Canada, analysing the interaction between endoparasites and winter tick loads in moose Alces alces. Though they found no synergistic effect on body condition, their findings demonstrate the ecological complexity of multi-parasite interactions and the potential for changing climates to alter host–parasite dynamics in the future, a fact that management could already account for. The next two papers focus on less commonly studied pathogen groups in wildlife disease ecology – bacteria and fungi, respectively. Dabhi et al. (2025) compared antibiotic resistance in microbial communities found in wild and captive sloth bears using non-invasive scat sampling. They found that captive bears harboured more human-associated pathogens and significantly higher levels of antibiotic resistance than wild bears, likely due to closer human contact and diet differences. These findings suggest antibiotic resistance to be useful as an indicator of human impact on wildlife and emphasize the importance of monitoring antibiotic resistance for both conservation and public health management. At a broader spatial scale, Delia Basanta et al. (2023) used a novel modelling approach to map the global epidemiological landscape of Batrachochytrium dendrobatidis (Bd), the fungal pathogen responsible for amphibian chytridiomycosis and a major contributor to amphibian declines. The study identified climate, species identity, and environmental factors as key drivers of Bd prevalence and highlights areas of high risk and potential refuges, offering tools to guide conservation priorities. Notably, the study found a negative correlation between amphibian species richness and Bd prevalence, suggesting a possible dilution effect. The final two papers deal explicitly with disease management in large mammals. Waller et al. (2024) examined how wild boar movements in Russia's Far East, influenced by fluctuating food availability, could affect the spread of African swine fever (ASF), a highly contagious viral disease. During a year of low acorn availability, wild boar travelled long distances – up to 77 km in four days – heightening the risk of rapid ASF transmission. The findings emphasise the importance of accounting for rare, resource-driven movements in disease spread models. In contrast, Mysterud et al. (2024) provide a retrospective on Norway's controversial and ambitious effort to contain chronic wasting disease, a fatal neurodegenerative prion disease, in wild reindeer Rangifer tarandus. This review paper documents the development of scientific, political, and stakeholder responses over seven years and highlights how implementation uncertainty and public pressure can derail even well-founded disease control strategies. It is a sobering reminder that disease management is as much about governance and communication as it is about biology. Host susceptibility varies across species and demographic groups. Host susceptibility and parasite load often vary not only among species but also within them, following clear demographic trends. Studies on blood parasites in reptiles (Marzal et al. 2024), and helminths in ungulates (König and Ehrmantraut 2024) illustrate that certain age groups or sexes tend to carry higher parasite burdens. These patterns are critical for both conservation and harvest-based wildlife management. For instance, elevated infection in younger animals could hinder recruitment, while parasite-induced weight loss may reduce carcass quality and economic returns from game meat. Parasite prevalence is shaped by landscape and host movement. Several studies (Delia Basanta et al. 2023, König and Ehrmantraut 2024) show that parasite prevalence correlates with environmental features such as wetland proximity or mast-rich habitats. These findings suggest that spatially targeted interventions may be more effective than broad-scale efforts. However, interactions between multiple parasitic agents, such as ecto- and endoparasites in moose (Pouchet et al. 2024), can be complex and responsive to shifting environmental conditions. Moreover, host movement behavior plays a key role in transmission dynamics. Long-distance dispersal observed in wild boar (Waller et al. 2024) and seasonal migration in starlings (Rimša et al. 2024) illustrate how food scarcity and resource pulses can drive animal movement, potentially facilitating disease spread over large areas. These insights underscore the importance of integrating landscape ecology, resource availability, and host behavior into disease management planning. Anthropogenic influence leaves microbial traces. Dabhi et al. (2025) bring attention to the role of antibiotic resistance (AR) as a marker of human impact on wildlife health. Their comparison of microbial communities in wild and captive sloth bears revealed significantly higher levels of human-associated pathogens and AR in captive individuals. These findings emphasize the need to monitor microbial dynamics at the human–wildlife interface, both for effective conservation planning and to safeguard public health. Chronic and low-prevalence infections can still matter. Findings from Rimša et al. (2024) and Wild et al. (2024) challenge the assumption that low-level or chronic infections are inconsequential. Even when parasitemia is minimal, physiological effects such as altered immune profiles, reduced energetic levels or reduced body condition can emerge, especially in populations already burdened by habitat loss or other stressors. These cases highlight the need for ongoing health surveillance, even in species that appear outwardly healthy. Modeling tools may support prioritization. Large-scale ecological modeling, such as that employed by Delia Basanta et al. (2023) to map the distribution of Batrachochytrium dendrobatidis, demonstrates the power of data-driven tools in identifying high-risk areas and vulnerable species. Such models can inform conservation prioritization where resources are scarce and proactive action is essential. However, their predictive reliability under rapidly changing environmental conditions remains an open question. Climate change, land-use shifts, and evolving host–pathogen relationships all challenge our ability to extrapolate confidently into the future. Implementation hinges on social–political feasibility. Scientific understanding alone is not sufficient to ensure effective disease management. Mysterud et al. (2024) offer a sobering case study of chronic wasting disease control in Norway, where early, well-funded eradication efforts eventually stalled due to public opposition and lack of political consensus. Their analysis underscores the critical importance of stakeholder involvement, transparent communication, and adaptive governance in navigating complex social–ecological challenges. Collectively, the contributions to this special issue demonstrate that wildlife disease and its management are influenced by a range of ecological, behavioural, and social–political factors. Improved understanding of disease dynamics, host responses, and contextual drivers is essential for developing evidence-based approaches to disease monitoring and long-term wildlife and health management. – Contributions to this special issue were handled by subject editors Chistophe Bonenfant, Cecilia di Bernardi, Kaya Klop-Toker, Stephanie Kramer-Schadt, Christian Sonne, and Hideharu Tsukada. Submissions to this special issue were peer-reviewed by at least two reviewers, using the same criteria and standards as for regular Wildlife Biology manuscripts. Their recommendations were of great help to the editors in deciding whether to publish and to the authors in improving their manuscripts.

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