Vetnews | Maart 2026 10 « BACK TO CONTENTS Abstract: In today’s landscape of zoonotic pathogen outbreaks, the dilution effect theory, i.e., the theory that greater biodiversity can help curb pathogen transmission among wildlife, has gained significant attention. However, the positive link between animal diversity and pathogen richness urges us to apply this concept with caution. It is crucial to explore how conservation biology can safeguard human health by preventing the emergence of zoonotic diseases. By investigating the implications of conservation strategies on animal communities and pathogen transmission as well as the adaptive capabilities of pathogens, we propose that biodiversity conservation based on small reserves can effectively reduce pathogen spread in wildlife, provided certain measurable conditions are met. Given the urgent need to tackle both zoonosis disease emergence and biodiversity loss, these interventions should be prioritised and implemented without delay. Introduction The urgency to reverse the loss of biodiversity [1] has increased societal interest in environmental conservation, pushing it onto political agendas. However, many decision-makers remain hesitant to implement sustainable conservation programs [2]. The COVID-19 pandemic, driven by SARS-CoV-2, has highlighted the global threat of zoonotic diseases, which jump from animals to humans, causing significant health, social, and economic disruptions. No longer just a topic for debate, the emergence of zoonoses is now clearly linked to humaninduced changes in our natural environments [3]. While geopolitical factors and financial resources often dominate discussions on international policies, short-term economic costs tend to overshadow the long-term impacts of these decisions. A key barrier is the lack of demonstrated synergies among crises that would maximise investment. To tackle this, we need a comprehensive cost-effectiveness analysis of how different habitat conservation strategies can mitigate disease emergence, encouraging authorities to engage more actively. Since the groundbreaking research by Ostfeld and Keesing (2000), numerous studies have highlighted the potential prophylactic effects of biodiversity conservation on infectious disease transmission [4]. This is evidenced by a frequent negative correlation between species richness and pathogen transmission [5–7]. However, the so-called ‘dilution effect’ is often non-linear and predicting the impact of biodiversity protection on zoonosis emergence in humans remains complex [8]. Thus, leveraging conservation biology tools to reduce the risk of emerging infectious diseases [9] demands a deeper understanding of how the dilution effect applies across various ecosystems [10–12] and processes, such as those involved in biodiversity loss [13]. Most studies focus on transmission dynamics within ecosystems, particularly whether altered pathogens are zoonotic [13,14]. However, pathogen circulation among animals is just the initial step toward spillover, overlooking critical animal-human interactions that biodiversity protection could influence. To safeguard human health, we must examine both the biological and sociological links between biodiversity loss and human exposure to zoonotic diseases, including direct human-animal interactions. Recent studies linking conservation strategies and infectious diseases highlight a significant dependence on local contexts and the specific pathogens involved [15]. It is important to point out here that we use the term “pathogen” to represent any kind of parasitic microbe. Obviously, the host spectrum and its adaptive potential (which are key components for a potential dilution effect) will be extremely different according to the kind of microbes considered (e.g., viruses, bacteria, helminths, etc.). This variability of contexts and community assemblages complicates efforts to identify universally applicable win-win solutions for environmental protection and public health. Unlike research on the dilution effect, these studies often prioritise human disease burden [16]. Since human disease burden depends on pathogen circulation, socio-economic factors, and pathogen adaptation (whether partial or complete), this perspective falls short in explaining how biodiversity conservation reduces spillover risks [17]. While the general applicability of the dilution effect has garnered considerable support [6,8,12,13,18], it is evident that policies rooted in this effect cannot be universally applied across all diseases and contexts. Leveraging Small Biodiversity Reserves to Prevent Zoonotic Disease: Insights from Dilution Effect and Pathogen Adaptation Theories Audrey Arnal, Rodolphe Elie Gozlan, Nathalie Charbonnel, Marie Bouilloud, Andrea Chaves, Manon Lounnas, Michel Gauthier-Clerc , Ana L. Vigueras-Galván, Céline Arnathau, David Roiz, Ana I. Bento, Serge Morand, Chris Walzer, Gerardo Suzán, Rosa Elena Sarmiento Silva, and Benjamin Roche
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