The available data on the Bartonella species have expanded rapidly in recent years as this group of organisms has been found to be responsible for a growing spectrum of emerging and reemerging diseases. We now have new insights into the natural history of the Bartonella species and can see that these bacteria have adapted to their mammalian reservoir hosts in unique ways. They cause chronic intraerythrocytic infections, with up to half of the reservoir host populations being bacteremic at any one time. This bacteremia is the source of the vector infection. The Bartonella bacteremias, however, result in few (and, if present, very subtle) clinical signs in their specific reservoir hosts, and this contradicts Koch’s observation that the blood of healthy humans or animals is free of bacteria.
Clinical and Diagnostic Laboratory Immunology
Clin Diagn Lab Immunol. 2002 Jan;9(1):8-18