(3) However, the
occurrence of an infected reservoir host in certain environment alone does not
pose a risk of pathogen spill-over to a target host population (i.e. companion
animals), especially in case the competent vector is absent (Hodo and Hamer,
2017). Tick vector responsible for the transmission of Babesia cf. microti is currently
unknown, but two species namely I.
hexagonus and Dermacentor reticulatus
are the main candidates proposed (Camacho et al., 2003; Hodži? et al.,
2017a). To date, only two ixodid tick species, Rhipicephalus sanguineus s.l. and R. turanicus have been experimentally demonstrated as definitive
hosts and vectors for H. canis
(Baneth et al., 2007; Giannelli et al., 2017a). All of the abovementioned tick
species are able to feed on both foxes and dogs (Lorusso et al., 2011; Sobrino
et al., 2012; Najm et al., 2014a; D´Amico et al., 2017a; Giannelli et al.,
2017a; Sándor et al., 2017) allowing the bidirectional pathogen exchange.
However, some blood-borne infectious agents can even be transmitted vertically
or directly by bites in mammalian host, ensuring their maintenance in the host
population without implication of tick vectors (Alvarado-Rybak et al., 2016).
The hypothesis about the existence of non-vectorial routes of H. canis transmission (H2) was driven by the fact that the
apicomplexan parasite has been reported in animals from areas well outside the
geographical range of its tick vectors, including Austria (Duscher et al.,
2014), Hungary (Hornok et al., 2013; Farkas et al., 2014), the Czech Republic
(Mitková et al., 2016) and Slovakia (Majláthová et al., 2007; Miterpáková et
al., 2017). Vertical transmission of H.
canis is known to occur in dogs (Murata et al., 1993), but it has never
been demonstrated in foxes. Therefore, we tested internal organs from six
partially developed foetuses retrieved from a H. canis-infected vixen from Austria by PCR and sequencing, and
found two of them infected with the same genetic variant as the respective
mother fox, which indicate the possible intrauterine infection. The vertical
transmission pathway in foxes could explain the high prevalence of H. canis in areas considered free of the
competent tick vectors. Nonetheless, possible transmission by vectors other
than Rhipicephalus ticks should also
be considered (Mitková et al., 2016). In addition, fox predation on wild rodents
has been discussed as another alternative mode of H. canis transmission (Hornok et al., 2013; Cardoso et al., 2014),
as proven for Hepatozoon americanum
(Johnson et al., 2009). However, some studies have shown that rodents are
infected with another Hepatozoon sp.,
genetically distinct from H. canis (Dež?ek
et al., 2010; Hamšíková et al., 2016) and probably do not play role in the
circulation and transmission of H. canis.
(4) In the context of possible spill-over of Babesia cf. microti and H. canis between foxes and dogs (H3), we examined the population genetic
structure of the parasites and the relationships between haplotypes derived
from domestic and wildlife species in different geographical regions. The
Median-Joining network constructed with the 18S rRNA nucleotide sequences
revealed a considerably higher level of overall genetic diversity of H. canis compared to Babesia cf. microti. However, there was no any correlation between geographic
locality, host and haplotype which could pinpoint the origin of infections.
Contemporary populations of Babesia
cf. microti and H. canis infecting foxes and dogs in Europe is represented by eight
and 26 unique haplotypes, respectively. Among them, one haplotype of Babesia cf. microti and four haplotypes of H.
canis are shared, which indirectly demonstrate the close interface and the
occurrence of the common transmission pattern between the cohabiting
populations of the animals. The relatively high prevalence of H. canis infection observed in shepherd
(Hornok et al., 2013) and fox bolting dogs (Mitková et al., 2016) may interpret
the foxes as a source of infections for the dogs in peridomestic areas.
Moreover, higher overall prevalence of the infection in foxes compared to that
in dogs may suggest the association of nidicolous ticks in H. canis transmission (Mitková et al., 2016). Interestingly,
despite very heterogeneous population of H.
canis in Europe, all 151 foxes from western Austria tested positive by PCR
and sequencing were infected with the same haplotype. Genetic structure of
pathogens is mainly defined by the animal host and arthropod vector population
dynamics as well as the host population size (Margos et al., 2012; Blasco-Costa
and Poulin, 2013; Mazé-Guilmo et al., 2016). The altitudes higher than 1000 m in
combination with narrow land passes (up to 70 km wide) seem to limit fox
migration (Galov et al., 2014) and consequently inhibit the host and parasite
gene flow displaying more pronounced genetic structure (Blasco-Costa and
Poulin, 2013). Therefore, comparative genetic population studies on wild
carnivore phylogeographic structuring using microsatellite analyses, would give
us very important information on pathogen circulation and host-pathogen
interactions, since distinct subpopulation of animals might be more prone to
infections. An extremely low degree of nucleotide diversity and relatively low
prevalence of H. canis in foxes from
the mountainous part of western Austria compared to other localities in Europe may
also propose very recent introduction of the parasite in the studied area.