First detection of rickettsiae in a US chigger population and the potential risk to people

点击翻译按钮获取中文摘要

Project Summary/Abstract Trombiculid mites belonging to several genera (Ascoschoengastia, Eutrombicula, Neotrombicula, Leptotrombidium, etc.) demonstrate a unique mode of parasitism compared to other medically important arthropod vectors. Particularly, the genus Leptotrombidium is the exclusive biological vector of scrub typhus, caused by Orientia tsutsugamushi (Ot), an obligate intracellular Gram-negative bacterium closely related to the genus Rickettsia (Rickettsiales: Rickettsiaceae). This disease is a significant source of morbidity and mortality; an estimated billion people are at risk and approximately one million cases are reported each year. Scrub typhus occurs in Korea, Japan, throughout southern Asia, the Asian-Pacific region, and northern Australia. More recently, scrub typhus reports in the Middle East, southern Chile, and Africa have reshaped our thinking about the epidemiological of this disease, suggesting it has a wider geographical distribution. Despite the growing number of studies and discoveries of chigger-borne human disease outside of the Tsutsugamushi Triangle, the role of chiggers in human infection of rickettsial pathogens in the US is still a total unknown. We have preliminary data that chiggers collected from NC are infected with Rickettsia species. Examining the prevalence of rickettsiae in chiggers is significant because chiggers in the US feed on the same animal reservoirs as ticks that carry and transmit human diseases, and there is the potential that human diseases attributed to ticks might be from chiggers. In this proposal, we will detect and determine the prevalence of rickettsiae DNA in chigger samples from different rodent species and for free-living (unfed, host-seeking) chiggers in North Carolina. Also, investigate for the first time the bacterial microbiome of chiggers in the North Carolina. This study will investigate the impact of host feeding versus transovarial transmission on the chigger pathogen, the association of bacteria with specific mite and animal species, and the relationship between chigger microbiome composition, endosymbiont interactions, and vector competency. This proposal exactly fits the goal of the R03 grants program, assessing the health risk to humans of chigger bites, which is a complete black box (has never been conducted before in the US). Similar studies on other continents, including South America, have found chiggers to harbor human pathogens.