What is the evidence that ecosystem components or functions have an impact on infectious diseases? A systematic review protocol

BACKGROUND: Many infectious pathogens can be transmitted from animals to humans and vice versa, or by animals (especially arthropods) to humans. Such diseases are called zoonotic and/or vector-borne diseases. To control or prevent them, it is often recommended to target population reduction of host or vector species, through preventive culling or insecticide use for example. But these types of destructive interventions have shown several limits altering their efficiency, including acquired resistance of arthropods to insecticides, unpredicted change in the ecology of host populations, unexpected negative functional consequences on ecosystems, as well as economic embrittlement when livestock is concerned. An alternative pathway of action would be to rely on the functioning of ecosystems, and on their careful management, to regulate diseases and thus reduce their impact on human health. In this perspective, a thorough evaluation of the conditions that can potentially promote such a positive regulation of infectious pathogens by ecosystems, and their efficiency, is needed. Here, we present the protocol of a systematic review that will evaluate the scientific evidence existing on potential links between ecosystem components or functions and 14 vector-borne and zoonotic diseases impacting human health. METHODS: We will search for studies that tested the effect of changes in (i) biological communities, and (ii) habitats and landscapes, on diseases. Scientific literature from 5 publication databases will be screened in a 3-rounds process: title, abstract and full-text screening. At each stage, articles will be either rejected or kept for the next round, depending on whether they fall in the exclusion or inclusion criteria. We will present results in two parts: a systematic map and a systematic review. The systematic map will present, for the 14 diseases, the number of publications, their geographical distribution, the type of ecosystem component/function they studied, as well as the host(s) in which epidemiological measurements have been performed. From this systematic map, we will identify groups of articles that allow for critical appraisal, i.e. groups of articles that studied the effect of the same ecosystem component/function on the same disease. Only those articles will be included in the systematic review. The validity of these articles will be assessed by critical appraisal and presented as a narrative synthesis with confidence levels.