Wild animals are obviously important for the maintenance of ticks and the long-term persistence of pathogens, often acting as a blood meal resource and as a reservoir or host for amplification, respectively (Lorusso et al., 2011; Rizzoli et al. , 2014). Among others, red foxes are the most examined wild carnivore species in Europe, mainly due to their high population density and wide distribution (Mitková et al., 2017). Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Consequently, they have been suggested as reservoirs for several TBPs, including those affecting companion animals and humans (Cardoso et al., 2015; Hodžić et al., 2015; Liesner et al., 2016; Ebani et al., 2017), but their status as a reservoir has yet to be demonstrated (Lorusso et al., 2011). The main aim of the present project was to study the presence and genetic diversity of tick-associated pathogens in foxes and to estimate their reservoir competence based on the data obtained here and those available in published scientific literature. To test our hypothesis (H1), we analyzed blood and spleen samples from 506 foxes originating from two westernmost Austrian provinces, namely Tyrol and Vorarlberg, for common pathogens derived from arthropod vectors (Publication 1). As a result of the comprehensive molecular study, foxes in Austria were found to harbor a considerable number of pathogens of veterinary and public health importance, including: Babesia Canis, Babesia cf. microti (syn. Theileria annae, Babesia microti-like, Babesia vulpes), Hepatozoon canis, Anaplasma phagocytophilum, Candidatus Neoehrlichia sp. (FU98) and Bartonella rochalimae. Corresponding to the results of other European studies (Duscher et al., 2014; Hodžić et al., 2015; Tolnai et al., 2015; Ebani et al., 2017), Babesia cf. microti and H. gru were the most prevalent pathogens in the foxes studied. The high prevalence and wide geographical spread of these two hematozoan parasites infecting foxes throughout almost all of Europe are the main reasons why they have been proposed as a main reservoir candidate. However, the high rate of infections in itself does not necessarily qualify the host as a reservoir (Rizzoli et al., 2014; Alvarado-Rybak et al., 2016; Hodo and Hamer, 2017) and only indicates exposure to the pathogen or its pathogens. carrier status (Estrada-Peña and de la Fuente, 2014; Hodo and Hamer, 2017). Therefore, the reservoir role of a given animal species can only be unequivocally demonstrated through xenodiagnostic and transmission experiments (Rizzoli et al., 2014). Unfortunately, such studies are rare and have not been conducted for most TBPs, so the reservoir status of wild animals, especially carnivores, involved in their natural transmission cycles still remains unknown (Rizzoli et al., 2014) . This primarily reflects difficulties in maintaining long-term captive wild animal colonies for experimental transmission studies (Roque and Jansen, 2014). However, prevalence in combination with other data provides a constructive framework for estimating reservoir potential in the absence of such experimental studies (Gürtler and Cardinal, 2015; Hodo and Hamer, 2017). The conceptual approach has already been used to evaluate reservoir host competence and the role of domestic and wild species in the transmission of Trypanosoma cruzi (Kinetoplastida: Trypanosomatidae), and may be applicable to any multihost pathogen transmission system (Gürtler and Cardinal, 2015; Hodo and Hamer,2017), including Babesia cf. microti and H. canis. Therefore, the thesis findings are discussed in light of the following criteria: (1) host susceptibility, (2) host infectivity to the tick vector, (3) tick-host contact, and (4) host-host haplotype associations parasite. Relative host susceptibility is defined as the proportion or probability of the exposed host animal contracting the infection and can be calculated from epidemiological studies reporting the prevalence of infections (Hodo and Hamer, 2017). Babesia cf. microti and H. canis are evidently the most common parasites hosted by red foxes in Europe, with overall detection rates ranging from 1% (Zanet et al., 2014) to 69.2% (Cardoso et al., 2013) , and 7.8 % (Farkas et al., 2014) at 100% (Criado-Fornelio et al., 2003), respectively (Supplementary material). The large discrepancy in prevalence between studies can be attributed to geographic location, abundance and density of tick vectors, population size of red foxes, and sensitivity of PCR tests (Cardoso et al., 2013). However, the results of our study revealed that the infection rate is highly dependent on the tissue used for molecular detection. We observed that blood is statistically more frequently infected with Babesia cf. microti compared to the spleen, while the spleen shows the highest level of H. canis infection compared to the blood. Therefore, for comparative purposes an overall aggregate prevalence of infection should be used, i.e. the total number of positive animals/a total number of animals tested in all published reports (Hodo and Hamer, 2017) rather than direct comparison of prevalence as it is often misleading (Gürtler and Cardinal, 2015). An overall infection rate above 20% has been proposed as one of the criteria used for reservoir host identification (Gürtler and Cardinal, 2015). The overall aggregate prevalence of Babesia see microti and H. canis in foxes in Europe, calculated on the basis of available molecular genetic studies, are estimated at 23.9% and 28.4%, respectively (supplementary material). However, the golden jackal (Canis aureus) and the raccoon dog (Nyctereutes procyonoides) are two other wild carnivore species recently recognized as suitable hosts and potential reservoirs for Babesia cf. microti (Mitková et al., 2017; Duscher et al., 2017) and H. canis (Duscher et al., 2013; Farkas et al., 2014; Mitková et al., 2017). However, their role in the eco-epidemiology of blood parasites is uncertain and requires more in-depth studies involving a larger number of samples from different geographic regions. Furthermore, the ability of a suspected reservoir host to infect a tick vector (host infectivity) is not equally distributed in the host population, and the transmission pattern is mainly determined by the host (e.g., genetic constitution, body mass, sex , behavior) and the environment. factors (Hersh et al., 2012; Roque and Jansen, 2014). Consequently, the reservoir capacity of a given host animal may be different at different locations and time points (Estrada-Peña and de la Fuente, 2014). In the absence of xenodiagnostic investigations, the presence of a parasite in the blood observed by cytology or PCR can be used as an indicator to calculate the infectivity index (Hodo and Hamer, 2017). The number of studies in which blood has been used for parasite detection in foxes is considerably lower than in those using the spleen and have shown a pooled infectivity index for Babesia cf. microti and H. canis by 39.1% and 19.5%, respectively (supplemental material). 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