Hotspots of interactions
Emerging infectious disease outbreaks have been documented globally, with hotspots identified in eastern North America, western Europe, Japan, and Oceania (Jones et al. 2008). Numerous but more sparse outbreaks have also been detected in South America outside of Amazonia, sub-Saharan Africa, and southern Asia, many of which continue to pose high risk for future outbreaks (Jones et al. 2008, Han et al. 2016, Allen et al. 2017). Our results partially mirror these trends, with our study identifying high numbers of reported human-wildlife interactions in Brazil, China, India, Nepal, Uganda, and the United States. While publication reports from these countries may be inflated due to reporting bias, several of these countries have regions of growing population densities where remaining natural lands continue to be developed for agriculture (Deng et al. 2009), making them high-risk areas for human-wildlife interactions. This overlap in patterns suggests that our data can be used to identify regions with opportunities for exposure to zoonotic pathogens, ultimately informing efforts to predict future EID outbreaks.
Our results further indicate common reports of human-wildlife interactions in agricultural portions of Africa and Asia akin to previous studies on zoonotic disease emergence. Areas of southern and eastern Asia and western and eastern Central Africa have previously been identified as regions with high potential for zoonotic disease emergence due to a combination of factors including high mammalian diversity, large tracts of remaining forest threatened by increasing rates of agriculturalization, and growing human populations (Grace et al. 2012, Allen et al. 2017, Jagadesh et al. 2022). Human populations in these regions of Africa and Asia with high rates of LUC may be exposed to an exceptional diversity of wildlife, providing ample opportunities for human interactions with novel wildlife pathogens (Allen et al. 2017). For example, LUC via agriculturalization destroys forested areas, leading to an increase in deforestation and creation of forest edges. While human-wildlife interactions occur across all land cover types, they are especially high in areas of intermediate LUC, where the increase of edge facilitates high levels of contact among humans, domestic animals, and wildlife (Kretser et al. 2008, Merkle et al. 2011, Faust et al. 2018). The abundance of human-wildlife interactions, and thereby potential for pathogen exposure, necessitates disease risk surveillance in these regions.
Urban regions in parts of Europe and North America have also been identified as high-risk areas for zoonotic pathogen transmission (Allen et al. 2017) and our results show that the urbanizing areas on these continents, and Oceania, are similarly hotspots for reports of human-wildlife interactions. While some of this weight may be from reporting bias, urbanizing areas in these continents are facing growing human populations due to myriad reasons, including better healthcare for resident populations, the increasing rate of rural to urban migration, and movement from the global south to the global north (de Haas et al. 2019). This increase in human population often leads to local environmental degradation, which can negatively affect the health of local wildlife species and create new opportunities for human-wildlife interactions that can lead to zoonotic pathogen transmission (Soulsbury and White 2015, Plowright et al. 2017, Weber and Sciubbba 2019). Subsequent reductions in environmental quality and local biodiversity have ramifications for zoonotic disease emergence, as generalist wildlife species able to cope with urbanization proliferate, increasing pathogen prevalence as they move into areas left vacant by more specialized species (Schmidt and Ostfeld 2001, Reusken and Heymann 2013, Hough 2014, Hassell et al. 2017).
Many of geographic hotspots for zoonotic disease emergence have been designated as such because of their high mammalian biodiversity (Allen et al. 2017, Wilkinson et al. 2018). Previous work has demonstrated that mammals represent a high risk for zoonotic pathogen transmission because of their phylogenetic relatedness to humans and the wide breadth of their ranges, which often facilitates close contact with humans (Streicker et al. 2010, Han et al. 2016, Olival et al. 2017). While all mammalian orders most often involved in human-wildlife interactions are known to harbor zoonotic pathogens, disease risk varies widely among these orders, mostly due to variations in within-order diversity (Mollentze and Streicker 2020). Groups like rodents (order: Rodentia) and primates (order: Primates) have been thoroughly investigated for their zoonotic pathogen potential due to their high species diversity and human relatedness, compared to elephants for example (order: Proboscidea), which have received comparatively less zoonotic pathogen surveillance attention (Johnson et al. 2015, Han et al. 2016, Olival et al. 2017). Our results show that disease surveillance efforts of these mammalian orders are particularly warranted given their repeated interactions with human and domestic animals stemming from growing rates of LUC (Johnson et al. 2015, Han et al. 2016, Olival et al. 2017).