Climate, vegetation, introduced hosts and trade shape a global wildlife pandemic

Abstract

Global factors, such as climate change, international trade and introductions of exotic species are often elicited as contributors to the unprecedented rate of disease emergence, but few studies have partitioned these factors for global pandemics. Although contemporary correlative species distribution models (SDMs) can be useful for predicting the spatial patterns of emerging diseases, they focus mainly on the fundamental niche (FN) predictors (i.e. abiotic climate and habitat factors), neglecting dispersal and propagule pressure predictors (PP, number of non-native individuals released into a region). Using a validated, predictive and global SDM, we show that both FN and PP accounted for significant, unique variation to the distribution of the chytrid fungus Batrachochytrium dendrobatidis (Bd), a pathogen implicated in the declines and extinctions of over 200 amphibian species worldwide. Bd was associated positively with vegetation, total trade and introduced amphibian hosts, nonlinearly with annual temperature range and non-significantly with amphibian leg trade or amphibian species richness. These findings provide a rare example where both FN and PP factors are predictive of a global pandemic. Our model should help guide management of this deadly pathogen and the development of other globally predictive models for species invasions and pathogen emergence influenced by FN and PP factors.

Spatial scale modulates the strength of ecological processes driving disease distributions

“…The third pathogen, the chytrid fungus Batrachochytrium dendrobatidis (Bd), is considered one of the deadliest organisms on the planet because of its association with hundreds of amphibian extinctions in the last half century (21,22). We chose to model the spatial factors affecting these pathogens because (i) spatially explicit datasets of their distributions were available (but were not available for other pathogens or other organisms in general; see Methods); (ii) they span a diversity of taxa (a virus, bacterium, and fungus) and transmission modes (WNV and Lyme are mosquito-and tick-borne, respectively, and Bd is a directly transmitted, water-borne pathogen), and infect various types of hosts (endothermic and ectothermic), increasing the generality of our findings; (iii) they are widespread generalists throughout the United States, providing a spatial extent great enough to conduct largescale analyses; (iv) their abundances or prevalences appear to be partially controlled by a common biotic factor, the richness of potential hosts (19,21,23,24), and by common abiotic factors, including climate and vegetation (20,25,26); and, finally, (v) understanding emerging diseases is of critical importance to biodiversity conservation and human health. Our goal was not to develop and put forth the best possible model to explain the spread of these diseases but rather to test whether spatial scale influences which types of ecological processes are important.…”

“…Human activities can alter the dispersal of organisms (even for species not expanding their ranges; see Supporting Information) (25) both by facilitating longdistance movements of nonnative species (28) and emerging pathogens (25,29) and by impeding spread by reducing habitat connectivity through habitat destruction and the construction of roads, canals, and buildings (30). Indeed, the distributions of all three pathogens have been reported to be affected by humans (20,25,29). Thus, we used human population density to represent the ways in which humans can affect pathogen transmission (e.g., through dispersal).…”

Filling a gap in the distribution of Batrachochytrium dendrobatidis: evidence in amphibians from northern China

“…The presence of Bd in all surveyed farms, food markets, and pet shops calls for urgent implementation of measures by the Chinese animal health authority to reduce the likelihood of Bd spill-over due to escapes or low (if not non-existent) water and residue management of aquaculture settings (Allan & Gartenstein 2010). If Bd is truly absent from wild environments of northeastern China, as has been previously predicted by Bd niche modeling (Rödder et al 2009, Liu et al 2013b), many native amphibian species or populations from this region may be naïve to Bd and therefore possibly highly susceptible to the population effects of chytridiomycosis (Cheng et al 2011).…”

Spatial distribution of Batrachochytrium dendrobatidis in South American caecilians

“…Service layer source: US National Park Service (Rödder et al 2009, Liu et al 2012, James et al 2015, Becker et al 2016. Although most of the Bdpositive records overlapped with reported areas of high climatic suitability for the fungus in the Neotropics (Rödder et al 2009, Liu et al 2012, James et al 2015, Becker et al 2016, several Bd-positive records extend far into areas of poor suitability for Bd in anurans (e.g. central Amazon: see Becker et al 2016).…”