Sarcocystis infection

Lesniak, Ines, Franz, Mathias, Heckmann, Ilja, Greenwood, Alex D., Hofer, Heribert & Krone, Oliver, 2017, Surrogate hosts: Hunting dogs and recolonizing grey wolves share their endoparasites, International Journal for Parasitology: Parasites and Wildlife 6 (3), pp. 278-286 : 281-283

4.1. Sarcocystis infection of hunting dogs and impact of wolves

We identified 11 known Sarcocystis species in hunting dogs.

Wolves have been previously shown to host as well 11 known Sarcocystis species ( Lesniak et al., 2017) of which eight were shared with hunting dogs in this study. These species included the two wolf specialists S. grueneri and S. taeniata that are known to occur in German roe deer ( Capreolus capreolus ) and red deer ( Cervus elaphus ) (Lesniak et al., under review), and hence serve as the most likely source of infection for hunting dogs. In contrast to our first prediction, overall Sarcocystis prevalence in hunting dogs did not significantly differ between wolf (63.3%) and control areas (65.5%). However, it is considerably lower than the overall Sarcocystis prevalence of 95% in wolves from Germany ( Lesniak et al., 2017), and much higher than previously reported prevalence between 2% and 9% in companion dogs from Germany ( Barutzki and Schaper, 2003, 2011). A likely explanation for the lack of a wolf‾associated increase in overall Sarcocystis prevalence is that in another study (1) a substantial increase was only documented in red deer, whereas in other ungulates the increase was only slight and limited to a non‾significant trend (Lesniak et al., under review), and that (2) this overall increase in Sarcocystis prevalence was mainly driven by the two wolf specialist species (Lesniak et al., under review). The current study demonstrates that hunting dog infection with S. grueneri ‾ but not with S. taeniata ‾ was more likely to occur when wolves were present. Consistent with the above mentioned study, wolves most likely increased the prevalence of S. grueneri in their ungulate prey species, thereby being indirectly responsible for an increase in prevalence in hunting dogs because Sarcocystis cannot be directly transmitted between canids but require an intermediate host ( Fig. 3B ). Hunting dogs had a lower prevalence of S. grueneri in control areas where wolves were absent. Until now, no other wild canids have been described as definitive hosts of S. grueneri and S. taeniata , which were not detected in genetic studies in red foxes and raccoon dogs (Prakas et al., 2015; More ́ et al., 2016).

Here, as elsewhere, hunting dogs and mesopredators are the most likely source of infection for grazing ungulates. A study of ungulates from the control area suggested that both S. grueneri and S. taeniata occur in roe deer but not in red deer (Lesniak et al., under review). In order to explain these findings we propose the following conceptual model of Sarcocystis transmission dynamics: parasite strains of species that are spread by hunting dogs in control areas are only well‾adapted to roe deer but not to red deer ( Fig. 3A ), whereas strains spread by wolves are well‾adapted to both cervids ( Fig. 3B ). Investigation of other definitive hosts, including studies using more variable genome sequences in order to identify parasite strains, would be required to either increase confidence in this model or reject it. Additionally, further (unknown) factors ‾ other than wolf absence or presence and dog age or sampling effort for which we had controlled in the respective linear models ‾ may potentially alter the parasite infection risk for hunting dogs and may vary between the two different study regions. Such limitations cannot be ruled out in field studies like this, and may therefore limit the conclusions that can be drawn from the results. For example, microclimate ( Randolph and Storey, 1999) or habitat structure, including husbandry types and (wildlife) host density and distribution ( Sousa and Grosholz, 1991) may influence survival and transmission of infectious parasite stages in the environment but have not been considered in this study. Nevertheless, our findings indicate that the presence of a returning definitive host, the grey wolf, seems to represent a low parasite infection risk for hunting dogs and is currently limited to one particular protozoan parasite.

Dog owners reported that their dogs receive remains of game such as roe deer, red deer, wild boar and moufflon as well as of farm animals such as cattle, horse and sheep (see Supplementary Table S1). According to a Canadian study, the feeding of commercial meat according to the Biologically Appropriate Raw Food (BARF) method has become an increasingly popular trend among pet owners ( Schlesinger and Joffe, 2011). Both raw‾feeding diets are potential sources of the high Sarcocystis prevalence and diversity detected in hunting dogs and may explain the lack of a systematic link between wolf presence and overall Sarcocystis prevalence or species richness in hunting dogs.

Figures

Fig. 3. S.grueneri and S.taeniata developmental cycles with their intermediate and definitive host in areas without wolves (A) and with wolves (B). In wolf habitats, wolves increase S. grueneri prevalence in their prey, in turn leading to a higher infection rate in hunting dogs. S.grueneri and S. taeniata strains spread by wolves are well‾adapted to both ungulate species, while S.grueneri and S. taeniata strains spread by hunting dogs from the control area are restricted to roe deer (right ungulate pictogram). The epidemiological influence of wolves regarding the spread of Sarcocystis in comparison to hunting dogs has a higher impact on red deer (left ungulate pictogram) than on roe deer. Sarcocystis strains in hunting dogs from the wolf area are likely to be a mixture of both dog and wolf strains. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)