Abstract
BackgroundRed deer (Cervus elaphus) are a common wild definitive host for liver fluke (Fasciola hepatica) that have been the subject of limited diagnostic surveillance. This study aimed to explore the extent to which coprological diagnoses for F. hepatica in red deer in the Scottish Highlands, Scotland, are associated with variability among hosts and habitats.MethodsOur analyses were based on coproantigen ELISA diagnoses derived from faecal samples that were collected from carcasses of culled deer on nine hunting estates during two sampling seasons. Sampling locations were used as centroids about which circular home ranges were quantified. Data were stratified by season, and associations between host, hydrological, land cover and meteorological variables and binary diagnoses during 2013–2014 (n = 390) were explored by mixed effect logistic regression. The ability of our model to predict diagnoses relative to that which would be expected by chance was quantified, and data collected during 2012–2013 (n = 289) were used to assess model transferability.ResultsDuring 2013–2014, habitat and host characteristics explained 28% of variation in diagnoses, whereby half of the explained variation was attributed to differences among estates. The probability of a positive diagnosis was positively associated with the length of streams in the immediate surroundings of each sampling location, but no non-zero relationships were found for land cover or lifetime average weather variables. Regardless of habitat, the probability of a positive diagnosis remained greatest for males, although males were always sampled earlier in the year than females. A slight decrease in prediction efficacy occurred when our model was used to predict diagnoses for out-of-sample data.ConclusionsWe are cautious to extrapolate our findings geographically, owing to a large proportion of variation attributable to overarching differences among estates. Nevertheless, the temporal transferability of our model is encouraging. While we did not identify any non-zero relationship between meteorological variables and probability of diagnosis, we attribute this (in part) to limitations of interpolated meteorological data. Further study into non-independent diagnoses within estates and differences among estates in terms of deer management, would improve our understanding of F. hepatica prevalence in wild deer.
Highlights
Red deer (Cervus elaphus) are a common wild definitive host for liver fluke (Fasciola hepatica) that have been the subject of limited diagnostic surveillance
Study sites, sampling methods and F. hepatica diagnoses Red deer faecal samples were collected by deer stalkers/ gamekeepers on unfenced Scottish Highland estates, which are managed largely for red deer stalking: Alladale (AL); Altnaharra (AT); Applecross Trust (AP); Ardnamurchan (AR); Badanloch (BA); Ben Loyal (BL); Conaglen (CO); North Harris Trust and Aline (NA); and Strathconon (ST) (Fig. 1; see “Methods” section of [17] for an ethics statement regarding the sampling of wild red deer for this study)
Our assumption of linear relationships between model covariates and the logit link transformed expectation of the response were validated by residual plots, though we noted a possible borderline non-linear relationship for smooth grassland (Additional file 1: Figure S1)
Summary
Red deer (Cervus elaphus) are a common wild definitive host for liver fluke (Fasciola hepatica) that have been the subject of limited diagnostic surveillance. F. hepatica occurrence in common wild definitive hosts, such as cervids, received only fleeting attention, e.g. as part of histopathological surveys of red (Cervus elaphus) and sika (Cervus nippon) deer in Scotland [4]. Where definitive and intermediate hosts are resident in a temperate climate, e.g. in a large proportion of GB (England and Wales), the summer risk of F. hepatica infection is predictable based on the principle that transmission is limited primarily by moisture during the summer months (i.e. the balance between rainfall and evapotranspiration; [12]). Drier regions can experience a negative correlation between F. hepatica incidence and rainfall (e.g. in Belgium; [13]), owing to an increase in fresh vegetation growth away from permanent water sources around (and in) which intermediate hosts reside
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