Human Infection withCandidatus Rickettsia tarasevichiae

Abstract

From May through August 2012, a total of 251 patients who had recent tick bites sought treatment at Mudanjiang Forestry Central Hospital in northeastern China and were tested for tickborne infections. Polymerase-chain-reaction testing followed by sequencing of eschar and blood samples showed that 5 patients were infected with Candidatus Rickettsia tarasevichiae, a new species of rickettsiae of the spotted fever group. Phylogenetic analysis based on either the citrate synthase gene or the outer-membrane protein A gene showed that the agent was genetically close to R. canadensis (see Fig. 1 in the Supplementary Appendix, available with the full text of this letter at NEJM.org), one of several “ancestral” rickettsiae that are suspected to be endosymbionts and nonpathogens.¹ In an indirect immunofluorescence assay, IgM or IgG antibodies reacted to two endemic species of rickettsiae of the spotted fever group, R. heilongjiangensis and R. sibirica.²