Sand lizards (Lacerta agilis) decrease nymphal infection prevalence for tick-borne pathogens Borrelia burgdorferi sensu lato and Anaplasma phagocytophilum in a coastal dune ecosystem

1. Understanding which factors determine tick-borne disease hazard can
contribute to effective disease control. In Europe, the hazard of the
pathogens Borrelia burgdorferi s.l. and Anaplasma phagocytophilum is
determined by local tick densities (mainly Ixodes ricinus) and the
reservoir competence of the host species community. Sand lizards (Lacerta
agilis) are common hosts for larvae and nymphs of I. ricinus and
non-competent reservoirs for both pathogens. Consequently, high relative
abundance of L. agilis is hypothesized to be associated with lower
infection prevalence in nymphs. Here, we aimed to test whether this
effectively occurs in natural settings. 2. We sampled different habitat
types within a heterogenous dune landscape at the Dutch coast and
estimated 1) L. agilis densities, 2) host community competence, 3) the
density and infection prevalence of questing I. ricinus ticks, and 4) the
number and infection prevalence of ticks feeding on L. agilis. 3. Captured
L. agilis had high tick burdens and contributed substantially to feeding
I. ricinus larvae in their natural habitat. B. burgdorferi s.l. and A.
phagocytophilum were virtually absent from feeding larvae and nymphs. 4.
The nymphal infection prevalence of both pathogens in questing ticks was
lower in habitat types where L. agilis was more abundant. Hence, L. agilis
strongly reduced community competence. 5. The density of questing nymphs
was higher in habitat types with denser vegetation and also varied more
between habitat types than infection prevalence. As a result, nymphal
density had a stronger effect on the density of infected ticks than did
nymphal infection prevalence. 6. Synthesis and applications. Coastal dune
habitats favourable for L. agilis have lower densities of questing nymphs,
and a lower human infection hazard. These results might be applicable to
similar ecosystems where L. agilis is present. From a public health
perspective, this underlines the importance of preserving early
successional habitat, as encroaching shrubs are associated with higher
tick-borne disease hazard, and vegetation removal might be a solution to
reduce hazard in coastal dunes. The high degree of spatial heterogeneity
in the abundance of tick-borne pathogens also poses opportunities to
manage recreational activities to limit human exposure to tick-borne
diseases.