Improved sensitivity of PCR for diagnosis of human granulocytic ehrlichiosis using epank1 genes of Ehrlichia phagocytophila-group Ehrlichiae

The agent of human granulocytic ehrlichiosis (HGE), Ehrlichia phagocytophil a, and Ehrlichia equi probably comprise variants of a single Ehrlichia spec ies now called the Ehrlichia phagocytophila genogroup, These variants share a unique 153-kDa protein antigen with ankyrin repeat motifs encoded by the epank1 gene. The epank1 gene was investigated as an improved target for PC R diagnosis of HGE compared with the currently used 16S rRNA gene target. P rimers for epank1 flanking a region that spans part of the 5' ankyrin repea t coding region and part of the unique 3' region were synthesized. Blood sa mples from 31 patients with suspected HGE who were previously tested by 16S rRNA gene (16S) PCR and indirect immunofluorescent antibody test (IFA) wer e retrospectively tested with the epank1 primers. Eleven patients were 16S PCR positive and had a seroconversion detected by IFA (group A), 10 patient s were 16S PCR negative but had a seroconversion detected by IFA (group B), and 10 patients were 16S PCR negative and seronegative (group C), Ten of t he 11 group A patients were epank1 PCR positive, all 10 of the group B pati ents were epank1 PCR positive, and all of the PCR-negative and seronegative patients (group C) were epank1 PCR negative. The epank1 primers are more s ensitive than the previously used 16S rRNA gene primers and therefore may b e more useful in diagnostic testing for HGE.