Ehrlichia is a genus of obligatory intracellular bacteria belonging to family Anaplasmataceae, order Rickettsiales. Until today, six formally recognized Ehrlichia species  and some Candidatus species have been reported [2-6]. They are mainly vectored by ticks and many of them are pathogenic to human or animals. E. canis, E. ruminantium and E. muris are pathogens for canines, ruminants and mice, respectively [7-9]. E. chaffeensis, E. ewingii, E. muris-like agent and E. canis have been reported to infect human and cause syndromes ranging from febrile to severe multiple organ failure [10-14]. The common symptoms of human ehrlichiosis are fever, headache, myalgia, malaise, weakness, nausea, leukopenia, vomiting, diarrhea, and abdominal pain . These uncharacteristic symptoms cause difficulties in diagnosis and may lead to misdiagnosis clinically. In China, multiple Ehrlichia species have been identified including E. chaffeensis, E. canis, E. ruminantium, etc, from ticks, mammals, mosquitoes and leeches [16-19] Until today, E. chaffeensis is the only known human Ehrlichial pathogen in China. Human granulocytic ehrlichiosis (HGE) disease caused by E. chaffeensis has been proved to be widespread in several provinces of China [16, 20-21]. Rural residents, especially farmers, are at substantially increased risk of Ehrlichia exposure .
Small mammals such as rodents have been proved to be the reservoirs of many Ehrlichia species. Ehrlichia sp. HF group has been identified in Apodemus argenteus, A. speciosus, Eothenomys smithi and Myodes rufocanus bedfordiae [23-25]. Candidatus E. khabarensis was identified and characterized from Myodes rutilus, M. rufocanus and Sorex araneus in Russian Far East . E. muris was first isolated from the tissue of a wild mouse (Eothenomys kageus) in Japan , while a human pathogenic E. muris-like agent was identified from Peromyscus leucopus in US . In the host-vector ecosystem, these Ehrlichia bacteria can be horizontally transmitted to ticks that infesting on the hosts, meanwhile, spillover into human populations may also occasionally occur. However, it is still unclear whether they pose a threat to public health. The solid evidence of their involvement in the human ehrlichiosis is still to be further studied.
Although the HGE has been common in China, the geographical distribution and genetic diversity of various Ehrlichia species have not yet been well studied. In Hainan Province, the investigations and studies on Ehrlichia have been very few . Hainan province consists of the second largest island of China locating in Southern China Sea. It has an area 33, 900 square kilometers and a population of about 9.34 million. Owing to the tropical climate and outstanding landscape, it is becoming a great tourist attraction and is receiving tens of millions of tourists each year. For better understanding on the Ehrlichia distribution and its potential risk to public health in Hainan Province, we examined the molecular evidence of Ehrlichia in wild rodents and a novel Ehrlichia species was characterized in this study.