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

Area of Science:

• Ecology
• Parasitology
• Evolutionary Biology

Background:

• Parasites infecting multiple host species are common, with transmission between hosts assumed to be frequent.
• This between-species transmission is considered crucial for parasite persistence and disease control, yet empirical evidence is scarce.
• The assumption of inevitable between-species transmission may be inaccurate in natural communities.

Purpose of the Study:

• To investigate the occurrence and barriers of between-species transmission in a multihost parasite system.
• To analyze flea-borne Bartonella parasites infecting sympatric wood mice (Apodemus sylvaticus) and bank voles (Myodes glareolus).
• To determine if genetic distinctiveness of parasites within each host species indicates limited transmission.

Main Methods:

• Genetic characterization of Bartonella parasites from infected wood mice and bank voles.
• Identification of flea species associated with each rodent host.
• Analysis of Bartonella variants carried by individual fleas to assess transmission routes and barriers.

Main Results:

• Multiple Bartonella species infected both wood mice and bank voles.
• Genetic analysis revealed distinct parasite assemblages for each host species, indicating covert host specificity and rare between-species transmission.
• Fleas were often host-generalists, but carried Bartonella variants reflecting their host species, suggesting encounter barriers. Some fleas carried variants not found in their host, indicating host-pathogen incompatibility.

Conclusions:

• Between-species transmission of Bartonella parasites between wood mice and bank voles is rare, contrary to common assumptions.
• Encounter barriers (limited flea transfer) and host-pathogen incompatibility limit parasite spread between sympatric hosts.
• Parasite populations can persist independently in different host species, challenging current understandings of disease dynamics and control in wildlife reservoirs.