Out of Asia? Vector switches leading to the expansion of Eurasian Lyme
disease bacteria
Abstract
Vector-borne pathogens exist in obligate transmission cycles between
vector and reservoir host species. Host shifts can lead to geographic
expansion and the emergence of new diseases. Three etiological agents of
human Lyme borreliosis (Borrelia afzelii, Borrelia bavariensis, and
Borrelia garinii) predominantly utilize two distinct tick species as
vectors in Asia (Ixodes persulcatus) and Europe (Ixodes ricinus) but how
and in which order they colonized each continent remains unknown. Here,
by reconstructing the evolutionary history of 142 Eurasian isolates, we
show that all three Borrelia genospecies evolved from an Asian origin,
suggesting that successful expansion into Europe resulted through
invading a novel vector. The pattern of gene flow between continents is
different between genospecies and most likely conditioned by reservoir
host association and their dispersal. Our results highlight that
Eurasian Lyme borreliosis agents are all capable of geographic expansion
through vector shifts, but potentially differ in their capacity as
emergent pathogens.