Serologic Evidence of Human Exposure to Ehrlichiosis Agents in Japan

Abstract

In retrospective analyses, we report 3 febrile patients in Japan who had seroconversion to antibodies against Ehrlichia chaffeensis antigens detected by using an immunofluorescence and Western blot. Our results provide evidence of autochthonous human ehrlichiosis cases and indicate ehrlichiosis should be considered a potential cause of febrile illness in Japan.

Keywords: Ehrlichia sp.; Japan; P28 outer membrane proteins; antibody; bacteria; ehrlichiosis; parasites; seroconversion; vector-borne infections; zoonoses.

Figure

Western blots using serum samples from a febrile patient (case 1) in Wakayama Prefecture in study showing serologic evidence of human exposure to ehrlichiosis agents in Japan. Serum samples were collected from the patient on day 2 and 17 after onset of illness. Human THP-1 and canine DH82 cells were uninfected or infected with Ehrlichia chaffeensis . THP-1 cells were also infected with Anaplasma phagocytophilum. Cell lysates were separated and Western blot was performed as described (Appendix). We used uninfected THP-1 and DH82 cells as negative lysate controls. We used rabbit serum against recombinant P44 antigens specific for A. phagocytophilum and recombinant P28 antigens specific for E. chaffeensis (1:10,000 dilution) as positive serum controls. We used serum from a healthy donor as a negative control serum (Precision for Medicine, https://www.precisionbiospecimens.com). The patient’s serum samples and negative control serum were diluted 1:250 and used to probe the blots. We used alkaline-phosphatase-conjugated goat anti-human IgM μ-chain and anti-human IgG γ-chain (Thermo Fisher Scientific, https://www.thermofisher.com) as secondary antibodies. Arrows indicate E. chaffeensis-specific P28 antigens (encoded by a p28 multigene family). Arrowhead shows A. phagocytophilum-specific P44 antigen (encoded by a p44 multigene family).