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Pathogens such as bacteria, fungi and viruses are important components of soil and aquatic communities, where they can benefit from decaying and living organic matter, and may opportunistically infect human and animal hosts. One-third of human infectious diseases is constituted by sapronotic disease agents that are natural inhabitants of soil or aquatic ecosystems. They are capable of existing and reproducing in the environment outside of the host for extended periods of time. However, as ecological research on sapronosis is infrequent and epidemiological models are even rarer, very little information is currently available. Their importance is overlooked in medical and veterinary research, as well as the relationships between free environmental forms and those that are pathogenic. Here, using dynamical models in realistic aquatic metacommunity systems, we analyze sapronosis transmission, using the human pathogen Mycobacterium ulcerans that is responsible for Buruli ulcer. We show that the persistence of bacilli in aquatic ecosystems is driven by a seasonal upstream supply, and that the attachment and development of cells to aquatic living forms is essential for such pathogen persistence and population dynamics. Our work constitutes the first set of metacommunity models of sapronotic disease transmission, and is highly flexible for adaptation to other types of sapronosis. The importance of sapronotic agents on animal and human disease burden needs better understanding and new models of sapronosis disease ecology to guide the management and prevention of this important group of pathogens. Author summary: Bacterial pathogens responsible for sapronotic diseases represent a threat to public health, accounting for one-third of human infections. However, little is known about variations in infection risk in time and space, hence limiting control strategies development, due to a lack of research on these pathogens. In this study, we developed a first realistic mathematical model to describe the spatial and temporal dynamics of sapronotic bacteria and their interactions with wildlife in aquatic ecosystems. Our model allows identifying the characteristics of wildlife-sapronotic bacteria interactions that play the most important role in determining disease risks in animals and humans. [ABSTRACT FROM AUTHOR]

Changes in biodiversity may impact infectious disease transmission through multiple mechanisms. We explored the impact of biodiversity changes on the transmission of Amazonian leishmaniases, a group of wild zoonoses transmitted by phlebotomine sand flies (Psychodidae), which represent an important health burden in a region where biodiversity is both rich and threatened. Using molecular analyses of sand fly pools and blood‐fed dipterans, we characterized the disease system in forest sites in French Guiana undergoing different levels of human‐induced disturbance. We show that the prevalence of Leishmania parasites in sand flies correlates positively with the relative abundance of mammal species known as Leishmania reservoirs. In addition, Leishmania reservoirs tend to dominate in less diverse mammal communities, in accordance with the dilution effect hypothesis. This results in a negative relationship between Leishmania prevalence and mammal diversity. On the other hand, higher mammal diversity is associated with higher sand fly density, possibly because more diverse mammal communities harbor higher biomass and more abundant feeding resources for sand flies, although more research is needed to identify the factors that shape sand fly communities. As a consequence of these antagonistic effects, decreased mammal diversity comes with an increase of parasite prevalence in sand flies, but has no detectable impact on the density of infected sand flies. These results represent additional evidence that biodiversity changes may simultaneously dilute and amplify vector‐borne disease transmission through different mechanisms that need to be better understood before drawing generalities on the biodiversity‐disease relationship. see also the Perspective by Taal Levi and Aimee L. Massey [ABSTRACT FROM AUTHOR]

Résumé: Les crises sanitaires ont de tout temps révélé les dysfonctionnements des organisations et mis en avant des vérités. Dans cet article, j'aborde le sujet des sciences et de l'expertise scientifique et biomédicale dans la période de ces deux années de tempête virale. Au-delà, je m'interroge sur la construction de la pensée scientifique et biomédicale en temps de syndémies, où des crises et des catastrophes de natures diverses s'entrechoquent, et dont il est alors très difficile de démêler l'écheveau. À situation de crises syndémiques viennent se surajouter des confusions importantes entre sciences, expertises et décisions publiques, facilitant l'apparition de comportements immoraux en recherche et biomédecine mais aussi traduisant la fragilité institutionnelle des institutions publiques de la connaissance. Health crises have always revealed the dysfunctions of organizations and highlighted truths. In this article, I address the subject of science and scientific and biomedical expertise during the viral storm of the past two years. Beyond that, I consider the construction of scientific and biomedical thought in times of syndemics, when crises and disasters of various kinds collide and can be disentangled only with great difficulty. In such periods, there is significant confusion between science, expertise, and public decisions, which can facilitate the occurrence of immoral behavior in research and biomedicine, but also reflects the institutional fragility of public institutions of knowledge. [ABSTRACT FROM AUTHOR]

Résumé: Le concept « Une seule santé », désormais internationalement porté par l'Organisation des Nations unies pour l'alimentation et l'agriculture (FAO), l'Organisation mondiale de la santé animale (OIE), l'Organisation mondiale de la santé (OMS) et le Programme des Nations unies pour l'environnement (PNUE), prend toute sa dimension dans les territoires. Si l'état des milieux et des habitats impacte directement la santé humaine, mais aussi celle des animaux et des plantes, ceci se joue justement dans le fonctionnement et les dynamiques des socio-agro-écosystèmes. Ces territoires constituent aujourd'hui la bonne échelle d'observation, le bon maillage d'analyse mais aussi d'actions, prenant ainsi plus en compte l'importance des citoyens dans les choix et les décisions pour un futur durable. Les auteurs préconisent donc un temps d'expérimentation sous forme de recherches et d'analyses à effectuer sur quelques territoires ciblés, choisis pour leurs caractéristiques propres et les interrogations qu'ils suscitent (forte dégradation du territoire, des espaces et de la biodiversité versus territoire paysagé et diversifié) en termes de risques sanitaires (recrudescence de certaines maladies chroniques ou infectieuses). Ces expérimentations devraient être menées en interdisciplinaire, avec l'ensemble des acteurs locaux, et pourraient s'appuyer sur des observations citoyennes. De telles approches, avec possiblement des cohortes de personnes suivies, devraient porter sur des durées minimales de cinq ans. Elles permettraient de faire émerger des indicateurs « Une seule santé », bases des actions et politiques publiques correctrices, en faveur d'une seule santé. The full importance of the "One health" concept now internationally promoted by the FAO, OIE, WHO, and UNEP is seen in the territories. The state of environments and habitats directly impacts human, animal and plant health, each of which depends on the functioning and dynamics of socio-agro-ecosystems. These territories are ideal for observation, analysis but also for action, thus giving citizens more weight in the choices and decisions for a sustainable future. The authors therefore recommend a period of experimentation in the form of research and analysis to be carried out in a few selected territories, chosen for their specific characteristics and the questions they raise (degradation of territory, habitats and biodiversity versus landscaped and diversified territory) in terms of health risks (emergence of certain chronic or infectious diseases). These experiments should be carried out in interdisciplinary studies involving all the local actors and could be based on citizen observations and cohorts of people followed up for at least five years. The emerging health indicators would serve as bases for corrective public actions and policies, in favor of " One health " for all. [ABSTRACT FROM AUTHOR]