Experimental Evidence for Opposing Effects of High Deer Density on Tick-Borne Pathogen Prevalence and Hazard



Gandy, Sara Louise ORCID: 0000-0003-2579-4479, Kilbride, Elizabeth, Biek, Roman, Millins, Caroline ORCID: 0000-0002-2006-092X and Gilbert, Lucy
(2021) Experimental Evidence for Opposing Effects of High Deer Density on Tick-Borne Pathogen Prevalence and Hazard.

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Abstract

<jats:title>Abstract</jats:title> <jats:p><jats:bold>Background:</jats:bold> Identifying the mechanisms driving disease risk is challenging for multi-host pathogens, such as <jats:italic>Borrelia burgdorferi </jats:italic>s.l., the tick-borne bacteria causing Lyme disease. Deer are tick reproduction hosts but do not transmit <jats:italic>B. burgdorferi </jats:italic>s.l., whereas rodents and birds are competent transmission hosts. Here, we use a long-term deer exclosure experiment to test three mechanisms for how high deer density might shape <jats:italic>B. burgdorferi </jats:italic>s.l. prevalence in ticks: increased prevalence due to higher larval tick densities facilitating high transmission on rodents (M1); alternatively, reduced <jats:italic>B. burgdorferi </jats:italic>s.l. prevalence because more larval ticks feed on deer rather than transmission-competent rodents (dilution effect) (M2), potentially due to ecological cascades, whereby higher deer grazing pressure lowers vegetation which decreases rodent abundance thus reducing transmission (M3).<jats:bold>Methods: </jats:bold>In a large enclosure where red deer stags were kept at high density (32.5 deer/km²), we used an experimental design consisting of eight plots of 0.23ha, four being fenced to simulate the absence of deer and four that were accessible to deer. In each plot we measured the density of questing nymphs and nymphal infection prevalence in spring, summer and autumn and quantified vegetation height and density, and small mammal abundance <jats:bold>Results:</jats:bold> Prevalence tended to be lower, though not conclusively so, in high deer density plots compared to exclosures (predicted prevalence of 1.0% vs 2.2%), suggesting that the dilution (M2) and cascade (M3) mechanisms might outweigh the increased opportunities for transmission (M1). Presence of deer at high density led to lower vegetation and fewer rodents, consistent with an ecological cascade. However, Lyme disease hazard (density of infected <jats:italic>I. ricinus </jats:italic>nymphs) was five times higher in high deer density plots due to tick density being 18 times higher.<jats:bold>Conclusion: </jats:bold>High densities of tick reproduction hosts such as deer can drive up vector-borne disease hazard, despite the potential to simultaneously reduce pathogen prevalence. This has implications for environmental pathogen management and for deer management, although the impact of intermediate deer densities now needs testing.</jats:p>

Item Type: Article
Uncontrolled Keywords: Emerging Infectious Diseases, Vector-Borne Diseases, Infectious Diseases, Lyme Disease, Infection, 3 Good Health and Well Being
Divisions: Faculty of Health and Life Sciences
Faculty of Health and Life Sciences > Institute of Infection, Veterinary and Ecological Sciences
Depositing User: Symplectic Admin
Date Deposited: 09 Nov 2021 14:55
Last Modified: 12 Apr 2024 14:02
DOI: 10.21203/rs.3.rs-586674/v1
Open Access URL: https://www.researchsquare.com/article/rs-586674/v...
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3142970