Abstract
Lyme borreliosis is the most common vector-borne zoonosis in the northern hemisphere, and the pathogens causing Lyme borreliosis have distinct, incompletely described transmission cycles involving multiple host groups. The mammal community in Fennoscandia differs from continental Europe, and we have limited data on potential competent and incompetent hosts of the different genospecies of Borrelia burgdorferi sensu lato (sl) at the northern distribution ranges where Lyme borreliosis is emerging. We used qPCR to determine presence of B. burgdorferi sl in tissue samples (ear) from 16 mammalian species and questing ticks from Norway, and we sequenced the 5S–23 S rDNA intergenic spacer region to determine genospecies from 1449 qPCR-positive isolates obtaining 423 sequences. All infections coming from small rodents and shrews were linked to the genospecies B. afzelii, while B. burgdorferi sensu stricto (ss) was only found in red squirrels (Sciurus vulgaris). Red squirrels were also infected with B. afzelii and B. garinii. There was no evidence of B. burgdorferi sl infection in moose (Alces alces), red deer (Cervus elaphus) or roe deer (Capreolus capreolus), confirming the role of cervids as incompetent hosts. In infected questing ticks in the two western counties, B. afzelii (67% and 75%) dominated over B. garinii (27% and 21%) and with only a few recorded B. burgdorferi ss and B. valaisiana. B. burgdorferi ss were more common in adult ticks than in nymphs, consistent with a reservoir in squirrels. Our study identifies potential competent hosts for the different genospecies, which is key to understand transmission cycles at high latitudes of Europe.
Highlights
Understanding the transmission cycles of pathogens circulating in ecosystems is challenging for multi-host systems[1]
The B. burgdorferi sensu stricto pathogen probably migrated from Europe to North America some 60000 years ago[13] and this genospecies dominates in North America and evolved into strains infecting birds and small
With the exception of red squirrels, all sequences of the intergenic spacer region (IGS) in rodents and shrews were consistent with infections of B. afzelii
Summary
Understanding the transmission cycles of pathogens circulating in ecosystems is challenging for multi-host systems[1]. An important step to understand disease hazard is to determine for a given pathogen which hosts are competent and incompetent in different ecosystems. Among the more complicated enzootic transmission cycles are the ones linked to the generalist ticks of the Ixodidae family in the northern hemisphere[6,7,8] These generalist ticks transmit a range of pathogens among which the genospecies forming the Borrelia burgdorferi sensu lato (sl) complex causing Lyme borreliosis are the most common and widespread. It is important to understand the transmission dynamics of each of the different genospecies in different regions Ticks are expanding their geographical distribution in northern Europe[22,23], and Lyme disease incidence is documented to increase in both Norway[24,25] and Finland[26]. We determined the relative abundance of B. burgdorferi sl genospecies in questing ticks as a basis to understand the hazard of each genospecies known to cause different clinical manifestations
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