Rats of the genus Rattus are reservoir hosts for pathogenic Bartonella species: An Old World origin for a New World disease?

Bartonella species were isolated from the blood of 63 of 325 Rattus norvegi cus and Ii of 92 Rattus rattus from 13 sites in the United States and Portu gal. Infection in both Rattus species ranged from 0% (e.g., 0/87) to simila r to 60% (e.g., 35/62), A 337-bp fragment of the citrate synthase (gltA) ge ne amplified by polymerase chain reaction was sequenced from all 74 isolate s. Isolates from R. norvegicus were most similar to Bartonella elizabethae, isolated previously from a patient with endocarditis (93%-100% sequence si milarity), followed by Bartonella grahamii and other Bartonella species iso lated from Old World rodents (Clethrionomys species, Mus musculus, and Ratt us species). These data suggest that Rattus species are a reservoir host fo r pathogenic Bartonella species and are consistent with a hypothesized Old World origin for Bartonella species recovered from Rattus species introduce d into the Americas.