Orientia tsutsugamushi Bacteremia and Cytokine Levels in Vietnamese Scrub Typhus Patients

Abstract

Scrub typhus, caused by the intracellular bacterium Orientia tsutsugamushi , is a major cause of febrile illness in the Asia/Pacific region. Here, we implemented a novel real-time PCR and determined the relation of DNA target gene concentration with serum cytokine levels. The limit of detection of the novel real-time PCR was 1,062 DNA copies per ml of EDTA whole blood. Specificity was excellent as determined on a panel of blood- and skin-borne bacteria, including Rickettsia spp. as well as healthy Vietnamese blood donors. Bacterial DNA concentrations after 9 to 12 days from symptoms onset were significantly higher than in earlier or later periods ( P < 0.05). Significantly higher concentrations of gamma interferon (IFN-γ) and interleukin-10 (IL-10) occurred during the acute phase of disease (<10 days from onset) as opposed to the convalescent phase ( P < 0.05). No significant differences were observed between the acute and the convalescent phases for tumor necrosis factor alpha (TNF-α) and IL-1β concentrations. Regression analysis of DNA concentrations and cytokine levels identified a significant positive relationship for IL-10 ( P < 0.0182) but not for IFN-γ, TNF-α, and IL-1β. In conclusion, proinflammatory cytokines and IL-10 were differentially related to human bacteremia. They may thus be induced by different constituents of O. tsutsugamushi . As a future prospect in a clinical diagnostic laboratory, quantitative real-time PCR may serve as a reliable tool to monitor therapy and to detect treatment failure.