Abstract
Dicrocoelium dendriticum is a trematode that infects ruminant livestock and requires two different intermediate hosts to complete its lifecycle. Modelling the spatial distribution of this parasite can help to improve its management in higher risk regions. The aim of this research was to assess the constraints of using historical data sets when modelling the spatial distribution of helminth parasites in ruminants. A parasitological data set provided by CREMOPAR (Napoli, Italy) and covering most of Italy was used in this paper. A baseline model (Random Forest, VECMAP®) using the entire data set was first used to determine the minimal number of data points needed to build a stable model. Then, annual distribution models were computed and compared with the baseline model. The best prediction rate and statistical output were obtained for 2012 and the worst for 2016, even though the sample size of the former was significantly smaller than the latter. We discuss how this may be explained by the fact that in 2012, the samples were more evenly geographically distributed, whilst in 2016 most of the data were strongly clustered. It is concluded that the spatial distribution of the input data appears to be more important than the actual sample size when computing species distribution models. This is often a major issue when using historical data to develop spatial models. Such data sets often include sampling biases and large geographical gaps. If this bias is not corrected, the spatial distribution model outputs may display the sampling effort rather than the real species distribution.
Highlights
The lancet liver fluke Dicrocoelium dendriticum is a parasite of the bile ducts and gallbladder of different mammalian species, including humans [31, 34].The life cycle of this parasite requires two invertebrate intermediate hosts: one being a xerophilic terrestrial snail, and the other an ant [25].Clinical signs in ruminants are not usually manifest, even in severe infections, and major lesions, due to liver impairment are detectable only at post-mortem examination [31, 34]
The aim of this study was to evaluate the impact of sample size on model predictive performance for D. dendriticum in Italy, using a historical longitudinal data set of diagnostic data, and to evaluate the utility of opportunistic diagnostic data at a higher temporal resolution for predicting the distribution of this species
A Random Forest (RF) species distribution modelling algorithm was applied to D. dendriticum diagnosis data and environmental covariates to predict the spatial probability distribution of this species in Italy
Summary
The lancet liver fluke Dicrocoelium dendriticum is a parasite of the bile ducts and gallbladder of different mammalian species (mainly ruminants), including humans [31, 34]. Clinical signs in ruminants are not usually manifest, even in severe infections, and major lesions, due to liver impairment are detectable only at post-mortem examination [31, 34]. D. dendriticum is, together with Fasciola hepatica, one of the leading causes of discarded livers in the abattoir, with associated economic losses. Due to global climate change, seasonal and spatial patterns of parasites can alter [7]. This includes indirect effects of climate change such as management changes [32]. Animal movements and anti-helminthic resistance leading to treatment failure are important drivers that boost the presence of parasites [5, 15, 19, 28]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
