Bartonella Febrile Illness
Serum specimens from 114 patients hospitalized with a febrile illness were tested with an indirect immunofluorescence assay (IFA) using Bartonella antigens prepared from 6 species of sigmodontine rodents and 3 known human Bartonella pathogens: B. henselae, B. quintana, and B. elizabethae. Acute- and convalescent-phase serum samples from 5 of these patients showed seroconversion with an IFA titer ≥512 to rodent-associated Bartonella antigens. The highest titer was against antigen derived from the white-throated woodrat (Neotoma albigula), although this rodent is not necessarily implicated as the source of infection. Three of the 5 who seroconverted showed no cross-reaction to the 3 Bartonella human pathogens. Common clinical characteristics were fever, chills, myalgias, leukopenia, thrombocytopenia, and transaminasemia. Although antibodies to Bartonella are cross-reactive, high-titer seroconversions to rodent-associated Bartonella antigens in adults with common clinical characteristics should stimulate the search for additional Bartonella human pathogens.

The discovery of hantavirus pulmonary syndrome and its high death rate in the southwestern United States resulted in greater vigilance in evaluating patients with acute febrile illness, particularly those with thrombocytopenia. Clinicians soon became aware of substantial numbers of hospitalized patients with a severe flulike prodrome and thrombocytopenia. In spite of conventional culture and serologic analysis for known pathogens and diseases, including hantaviruses, plague, tularemia, relapsing fever, spotted fever, murine typhus, and Q fever, no diagnosis could be made. To assist physicians in identifying treatable pathogens, we submitted serum to reference laboratories for diagnostic seroassays directed at known pathogens and organisms not previously associated with human disease. A concept of the role of rodent-associated bartonellae as a cause of unexplained febrile illness in the western United States has been recently developed (M. Kosoy, pers. comm.). We considered the possibility that some cases in our study were caused by Bartonella species.

Among at least 20 known species and subspecies of Bartonella, 5 have been identified as causes of human disease in North America.B. henselae causes cat-scratch disease with regional lymphadenitis and occasionally hepatosplenic disease in the immunocompetent host, and bacillary angiomatosis, cerebritis, or peliosis hepatis in the immunocompromised host. Louseborne B. quintana causes trench fever, aseptic meningitis, bacteremia, endocarditis, or bacillary angiomatosis. Recently isolated cases of infection with B. elizabethae,B. vinsonii subsp. arupensis, and B. washoensis suggest that the spectrum of Bartonella infections may continue to expand.

Many mammals, including numerous species of rodents, are commensally infected with Bartonella species in North America. We sought serologic evidence for human bartonellae infection in serious febrile illnesses in the Four Corners region, using diverse Bartonella antigens in an indirect immunofluorescence assay (IFA). We report 7 years' cumulative experience in diagnostic referrals, including 5 cases showing seroconversion, and 4 cases with a single high titer, to Bartonella antigens derived from strains isolated from rodents, particularly the white-throated woodrat (Neotoma albigula) captured in New Mexico.