Human babesiosis in Europe has been attributed to infection with
Babesia divergens and, to a lesser extent, with
Babesia venatorum and
Babesia microti, which are all transmitted to humans through a bite of
Ixodes ricinus. These
Babesia species circulate in the Netherlands,
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Human babesiosis in Europe has been attributed to infection with
Babesia divergens and, to a lesser extent, with
Babesia venatorum and
Babesia microti, which are all transmitted to humans through a bite of
Ixodes ricinus. These
Babesia species circulate in the Netherlands, but autochthonous human babesiosis cases have not been reported so far. To gain more insight into the natural sources of these
Babesia species, their presence in reservoir hosts and in
I. ricinus was examined. Moreover, part of the ticks were tested for co-infections with other tick borne pathogens. In a cross-sectional study, qPCR-detection was used to determine the presence of
Babesia species in 4611 tissue samples from 27 mammalian species and 13 bird species. Reverse line blotting (RLB) and qPCR detection of
Babesia species were used to test 25,849 questing
I. ricinus. Fragments of the 18S rDNA and cytochrome c oxidase subunit I (COI) gene from PCR-positive isolates were sequenced for confirmation and species identification and species-specific PCR reactions were performed on samples with suspected mixed infections.
Babesia microti was found in two widespread rodent species:
Myodes glareolus and
Apodemus sylvaticus, whereas
B. divergens was detected in the geographically restricted
Cervus elaphus and
Bison bonasus, and occasionally in free-ranging
Ovis aries.
B. venatorum was detected in the ubiquitous
Capreolus capreolus, and occasionally in free-ranging
O. aries.
Species-specific PCR revealed co-infections in
C. capreolus and
C. elaphus, resulting in higher prevalence of
B. venatorum and
B. divergens than disclosed by qPCR detection, followed by 18S rDNA and COI sequencing. The non-zoonotic
Babesia species found were
Babesia capreoli,
Babesia vulpes, Babesia sp. deer clade
, and badger-associated
Babesia species. The infection rate of zoonotic
Babesia species in questing
I. ricinus ticks was higher for
Babesia clade I (2.6%) than
Babesia clade X (1.9%). Co-infection of
B. microti with
Borrelia burgdorferi sensu lato and
Neoehrlichia mikurensis in questing nymphs occurred more than expected, which reflects their mutual reservoir hosts, and suggests the possibility of co-transmission of these three pathogens to humans during a tick bite. The ubiquitous spread and abundance of
B. microti and
B. venatorum in their reservoir hosts and questing ticks imply some level of human exposure through tick bites. The restricted distribution of the wild reservoir hosts for
B. divergens and its low infection rate in ticks might contribute to the absence of reported autochthonous cases of human babesiosis in the Netherlands.
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