Bartonella species are highly fastidious, vector borne, zoonotic bacteria that cause persistent intraerythrocytic bacteremia and endotheliotropic infection in reservoir and incidental hosts. Based upon prior in vitro research, three Bartonella sp., B. bacilliformis, B. henselae, and B. quintana can induce proliferation of endothelial cells, and each species has been associated with in vivo formation of vasoproliferative tumors in human patients. In this study, we report the molecular detection of B. vinsonii subsp. berkhoffii, B. henselae, B. koehlerae, or DNA of two of these Bartonella species simultaneously in vasoproliferative hemangiopericytomas from a dog, a horse, and a red wolf and in systemic reactive angioendotheliomatosis lesions from cats and a steer. In addition, we provide documentation that B. vinsonii subsp. berkhoffii infections induce activation of hypoxia inducible factor-1 and production of vascular endothelial growth factor, thereby providing mechanistic evidence as to how these bacteria could contribute to the development of vasoproliferative lesions. Based upon these results, we suggest that a fourth species, B. vinsonii subsp. berkhoffii, should be added to the list of bartonellae that can induce vasoproliferative lesions and that infection with one or more Bartonella sp. may contribute to the pathogenesis of systemic reactive angioendotheliomatosis and hemangiopericytomas in animals.