Data from: Multihost Bartonella parasites display covert host specificity even when transmitted by generalist vectors

Many parasites infect multiple sympatric host species, and there is a
general assumption that parasite transmission between co-occurring host
species is commonplace. Such between-species transmission could be key to
parasite persistence within a disease reservoir and is consequently an
emerging focus for disease control. However, while a growing body of
theory indicates the potential importance of between-species transmission
for parasite persistence, conclusive empirical evidence from natural
communities is lacking, and the assumption that between-species
transmission is inevitable may therefore be wrong. We investigated the
occurrence of between-species transmission in a well-studied multihost
parasite system. We identified the flea-borne Bartonella parasites
infecting sympatric populations of Apodemus sylvaticus (wood mice) and
Myodes glareolus (bank voles) in the UK and confirmed that several
Bartonella species infect both rodent species. However, counter to
previous knowledge, genetic characterization of these parasites revealed
covert host specificity, where each host species is associated with a
distinct assemblage of genetic variants, indicating that between-species
transmission is rare. Limited between-species transmission could result
from rare encounters between one host species and the parasites infecting
another and/or host–parasite incompatibility. We investigated the
occurrence of such encounter and compatibility barriers by identifying the
flea species associated with each rodent host, and the Bartonella variants
carried by individual fleas. We found that the majority of fleas were
host-generalists but the assemblage of Bartonella variants in fleas tended
to reflect the assemblage of Bartonella variants in the host species they
were collected from, thus providing evidence of encounter barriers
mediated by limited between-species flea transfer. However, we also found
several fleas that were carrying variants never found in the host species
from which they were collected, indicating some degree of host–pathogen
incompatibility when barriers to encounter are overcome. Overall, these
findings challenge our default perceptions of multihost parasite
persistence, as they show that despite considerable overlaps in host
species ecology, separate populations of the same parasite species may
circulate and persist independently in different sympatric host species.
This questions our fundamental understanding of endemic transmission
dynamics and the control of infection within natural reservoir
communities.