An Entry-Triggering Protein ofEhrlichiaIs a New Vaccine Candidate against Tick-Borne Human Monocytic Ehrlichiosis

The incidence of tick-borne diseases has risen dramatically in the past two decades and continues to rise. Discovered in 1986 and designated a nationally notifiable disease in 1998 by the Centers for Disease Control and Prevention, human monocytic ehrlichiosis, which is caused by the bacterium Ehrlichia chaffeensis , is one of the most prevalent, life-threatening, emerging tick-borne zoonoses in the United States. We investigated the role of theE. chaffeensisprotein EtpE in transmission of the bacterium from tick to human cells and in vaccinated dogs with EtpE to assess the efficacy of vaccination againstE. chaffeensis-infected tick challenge. Our results help fill gaps in our understanding ofE. chaffeensis-derived protective antigens that could be used in a candidate vaccine for immunization of humans to counter tick-transmitted ehrlichiosis.