Zoonotic diseases—those that are transmitted to humans from non-human vertebrates—inflict a major burden on health globally. Medical advances have reduced some of this burden, but the problem of (re)emergence of zoonotic diseases still remains. This is partly due to pathogen spillover (i.e., cross-species transmission) from wildlife to humans and livestock. Spillover requires a pathogen to overcome multiple barriers. Thus, solutions that strengthen the ecological barriers of spillover (i.e., ecological levers) are needed, but are elusive in practice. In part, this is due to the complexity of the spillover process and the low probability of each spillover event. New methods to predict and target spillover could be beneficial. Here, we investigate the concept of pathogen sharing—the proportion of pathogens that are shared between different species—to unravel potential drivers of spillover. We conducted a meta-analysis of the top predictors of pathogen sharing across different taxonomic groups to determine the relative importance of these predictors at various taxonomic levels. We used meta-regression and confounder-controlling stratification analysis to quantify the relative impact of these predictors. Here, we discuss how these findings might inform effective ecological levers to prevent spillover, and the economic, political, and social implications for implementing such solutions.
Results/Conclusions
The top predictors of pathogen sharing across taxa are: host geographic range overlap, host life history traits, and host phylogenetic relatedness. At higher taxonomic levels, phylogenetic relatedness is the primary predictor of pathogen sharing relative to the other predictors considered here. However, at lower taxonomic levels, geographic range overlap followed by life history traits become more important for predicting pathogen sharing than phylogenetic relatedness. For example, the data suggest that the risk of disease spillover from particular bird groups to humans is primarily driven by the degree of genetic similarities, while spillover from wild carnivores, ungulates, bats, and primates to humans and livestock is primarily driven by habitat overlap and behavior. Thus, a strategy that minimizes genome reassortment, for example, could be a favorable ecological lever for avian viruses, whereas habitat modification could prove more effective for disease spillover from mammals. In the current era of global environmental change, we still need effective, long-lasting, scalable, and affordable solutions that can target the modifiable links in the complex chain of processes driving cross-species pathogen spillover.