Ann. N.Y. Acad. Sci. 990: 267–278 (2003). © 2003 New York Academy of Sciences. Clinical Impact of Persistent Bartonella Bacteremia in Humans and Animals BRUNO B. CHOMEL, a RICKIE W. KASTEN, a JANE E. SYKES, b HENRI-JEAN BOULOUIS, c AND EDWARD B. BREITSCHWERDT d a Department of Population Health and Reproduction, b Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, California 95616, USA c UMR 956, INRA/AFSSA/ENVA, Ecole Nationale Vétérinaire, 7 Avenue du Général de Gaulle, 94704 Maisons-Alfort, France d Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina 27606, USA ABSTRACT: Bartonella spp. are emerging vector-borne pathogens that cause persistent, often asymptomatic bacteremia in their natural hosts. As our knowledge progresses, it appears that chronic infection may actually predis- pose the host to mild, insidious nonspecific manifestations or induce, in select- ed instances, severe diseases. Persistent asymptomatic bacteremia is most common in animals that serve as the main reservoir for the specific Bartonella. In humans, these organisms are B. bacilliformis and B. quintana. Other Bar- tonella species, for which humans are not the natural reservoir, tend to cause persistent bacteremia only in immunodeficient individuals. In some of these individuals, endothelial cell proliferation may create lesions such as bacillary angiomatosis or bacillary peliosis. In cats, bacteremia of variable level and continuity may last for years. Some strains of B. henselae may induce clinical manifestations, including fever, mild neurological signs, reproductive disor- ders, whereas others do not induce clinically obvious disease. Reproductive disorders have also been reported in mice experimentally infected with B. birtlesii. Finally, canids constitute the most interesting naturally occurring ani- mal model for the human disease. Like immunocompetent people, healthy dogs only occasionally demonstrate long-term bacteremia when infected with Bar- tonella spp. However, some dogs develop severe clinical manifestations, such as endocarditis, and the pathologic spectrum associated with Bartonella spp. infection in domestic dogs is rapidly expanding and resembles the infrequently reported clinical entities observed in humans. In coyotes, persistent bactere- mia is more common than in domestic dogs. It will be of interest to determine if coyotes develop clinical or pathological indications of infection. KEYWORDS: Bartonella; vector-borne pathogens; bacteremia Address for correspondence: Bruno B. Chomel, D.V.M., Ph.D., School of Veterinary Med- icine, University of California, Davis, Davis, California 95616. Voice: 530-752-8112; fax: 530-752-2377. bbchomel@ucdavis.edu