IgM to Bartonella henselae in cat-scratch disease and during acute Epstein-Barr virus infection

The diagnostic value of IgM to Bartonella henselae was evaluated in 20 children with cat-scratch disease (CSD) and controls consisting of 20 blood donors and 20 children with enlarged lymph nodes without CSD by two indirect immunofluorescence assays (IFA). One was based on B. henselae cocultivated with Vero cells (host cell-associated IFA), and the other on B. henselae grown on agar (host cell-free IFA). With the host cell-associated IFA, 18 of 20 children with CSD revealed IgM, whereas only 14 did so with the host cell-free IFA. Sera of two blood donors as well as sera from three children with enlarged lymph nodes without CSD showed also positive IgM to cell-associated B. henselae. This study reveals that the IFA applied had sensitivities of 70-90% and specificities of 87.5-100% for detecting IgM to B. henselae. Additionally, 20 patients with IgM to Epstein-Barr virus (EBV) capsid antigen were tested for IgM to B. henselae. Sera of 16 and 9 of these patients revealed IgM to B. henselae with the host cell-associated and the host cell-free IFA, respectively. Using Western blot these sera were demonstrated to react against linearized proteins of Vero cells and of B. henselae. Thus, since acute EBV infection may substantially reduce the specificity of B. henselae-specific IgM tests, we conclude that diagnosis of CSD should be confirmed by a significant IgG titer to B. henselae or by detection of this pathogen.