Global fingerprint of humans on the distribution of Bartonella bacteria in mammals

As humans alter habitats and move themselves and their commensal animals around the globe they change the disease risk for themselves, their commensal animals and wildlife. Bartonella bacteria are prevalent in many mammalian taxa, responsible for numerous human infections and presumed to be an important emerging group of zoonoses. Understanding how this genus has evolved and passed between host taxa in the past can reveal not only how current patterns were established but identify potential mechanisms for future cross-species transmission. We analyzed patterns of Bartonella transmission and likely sources of spillover using the largest collection of Bartonella gltA genotypes assembled, 860 unique genotypes of Bartonella globally. We provide support for the hypothesis that this pathogenic genus originated as an environmental bacterium before becoming an insect commensal and finally vertebrate pathogen. We show that rodents and domestic animals serve as the reservoirs or at least key proximate host for most Bartonella genotypes in humans. We also find evidence of exchange of Bartonella between domestic animals and wildlife and between domestic animals, likely due to increased contact between all groups. Bartonella is a useful infection for tracing potential zoonoses and demonstrates another major impact of humans on the planet. Care should be taken to avoid contact between humans, domestic animals and wildlife to protect the health of all.