Water sources aggregate parasites, with increasing effects in more arid conditions

Abstract

Shifts in landscape heterogeneity and climate can influence animal behavior and movement in ways that profoundly alter disease transmission. Amid accelerating climate and land use changes, it is increasingly important to identify and monitor hotspots of increased animal activity and overlap where disease transmission is likely to occur. Water sources that are foci of animal activity have great potential to promote disease transmission, but there has been very little work to quantify this, nor any comparison across a range of hosts and climatic contexts. In the case of fecal-oral parasites, water resources can aggregate large groups of many different host species in small areas, concentrate infectious material, and function as disease hotspots. This may be exacerbated where water is scarce and for species that require frequent drinking water access. Working in an East African savanna, we show via experimental and observational methods that water sources increase the density of wild and domestic herbivore feces and thus, the concentration of fecal-oral parasites in the environment, by up to two orders of magnitude. Our results show that this effect is amplified in drier areas and following periods of low rainfall, creating dynamic and heterogeneous disease landscapes across space and time. In addition, we show via camera trapping methods that herbivore grazing behaviors that expose them to fecal-oral parasites are often increased at water sources relative to background sites, thereby creating landscape hotspots of potential disease transmission. Critically, this effect varies markedly by herbivore species, with strongest effects observed for two large, water-dependent animals that are of critical concern for conservation and development: elephants and cattle. When water availability is reduced – a global pattern that is increasing amid climate changes and growing anthropogenic water use – risk of parasite exposure may increase substantially, posing multiple threats to critical taxa. These findings are important for understanding shifting parasite dynamics for several threatened wildlife species and for pastoral livelihoods in response to changing water supply due to climate changes.

Divergent water requirements partition exposure risk to parasites in wild equids

“…Surface water serves as an attraction point for many species, and its effects on concentrating animals, their feces, and/or intermediate hosts and vectors, promoting parasite transmission, have been seen in many studies, including on red deer (Vicente et al, 2006), big‐horn sheep (Whiting et al, 2009), and the willow tit and crested tit (Krama et al, 2015). Such effects were recently demonstrated for a suite of herbivore species in our study area, with a particularly strong increase in parasite exposure risk close to water for elephants and cattle (Titcomb et al, 2021). Zebra dung density was not shown to change with distance from water, but this was based on 150‐m long transects; our study builds on this to show that, when measured at a greater spatial scale, zebra dung density declines with distance from water up to about a kilometer away.…”

“…Grevy's zebras should thus be able to range much farther from water holes and to graze in areas plains zebras and other more water‐dependent ungulates cannot reach. Because water holes serve as attraction points, we expect that dung would be more concentrated in proximity to water (Titcomb et al, 2021) and that plains zebras would be constrained to feed in areas with higher dung density. Active fecal avoidance (choosing to feed on grass swards uncontaminated with dung) is unlikely to be of great influence on exposure risk in zebras.…”

Large-herbivore nemabiomes: patterns of parasite diversity and sharing

“…Because sympatric herbivores share many of the same food and water resources that serve as transmission routes for gastrointestinal parasites [31], studies have constructed parasite-sharing networks (hosts connected to other hosts via shared parasites) using literature records or morphological identifications [18,32]. Such networks are useful because node-specific metrics can be used to identify hosts that are central in various ways, such as (a) those having many links to other species via their parasites (high degree); (b) those sharing parasites with many other hosts (high closeness centrality); (c) those sharing parasites with distinct groups, acting as bridges (high betweenness centrality); and (d) those sharing parasites with other well-connected hosts, thereby occupying core positions (high eigenvector centrality).…”