Echinococcus multilocularis

Mori, Kensuke, Liccioli, Stefano, Marceau, Danielle & Massolo, Alessandro, 2019, A community analysis approach to parasite transmission in multi-host systems: Assemblages of small mammal prey and Echinococcus multilocularis in an urban area in North America, International Journal for Parasitology: Parasites and Wildlife 9, pp. 49-55 : 53

4.1. Small prey assemblages and Echinococcus multilocularis

Our clustering analysis using Bray-Curtis similarity identified three clusters. Although the clusters structures were not statistically significant by SIMPROF test possibly due to small sample size, similar structure were observed in both relative abundances and percentage of species, and with different clustering algorithms, providing some confidence in classifying the small mammal assemblages to the three assemblage types. Assemblage 1 consisting of BM sites seemed to be highly susceptible to the transmission of Em, while assemblage 3 seemed to be least susceptible to Em transmission .

In our study area, the three small mammal species of most interest due to their known susceptibility to Em are deer mice, meadow voles, and southern red-backed voles ( Liccioli et al., 2013). Particularly interesting was the correlation of proportion of deer mice to assemblage 1, where the prevalence among DH was high ( Fig. 3b ). This is consistent with conclusions drawn by Liccioli et al. (2014) that proportion of susceptible species is the key factor in the transmission of the parasite. However, even though assemblage 1 and 2 had about same proportion of susceptible species, assemblage 1 was associated with higher prevalence in both DH and IH. Compared to assemblage 1, assemblage 2 had higher abundance of most species of small mammals ( Fig. 3a ). Therefore we suspect that higher abundance of small mammals in general, both susceptible and non-susceptible, led to dilution of exposure and reduced transmission ( Baudrot et al., 2016).

Any inference drawn from this cluster analysis is limited by the samples size - an issue associated with the low prevalence at which the parasite occurs in intermediate hosts, which likely caused the lack of statistical significance for the Fisher's exact test on the assemblage types and the presence of positive IHs. However, the patterns observed were in agreement with the theoretical studies ( Baudrot et al., 2016; Raoul et al., 2015).

Figures

Fig. 3. Plot of the Canonical Correlation Analysis on the principal coordinates (CAP) of small mammal assemblages in five parks and natural areas in urban Calgary, AB, Canada, 2012–2013, using the cluster as a grouping factor. The cluster 1 is on the lower right corner, cluster 2 is on the lower left corner, and cluster 3 is on the center to the top of the plot. The 45% similarity contour line is drawn based on the dendrogram in Fig. 2a. a) Vectors were overlaid showing the correlation with the abundances of each species to each cluster. The red vector shows the correlation with the abundance of all the susceptible species combined. b) Vectors were overlaid showing the correlation with the proportion of each species to each cluster. The red vector shows the correlation with the proportion of all the susceptible species. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)