A disease caused by bacteria in the Ehrlichia genus that is carried and transmitted to humans by ticks, probably the dog tick or Lone Star tick. For many people, exposure to the bacteria does not cause symptoms. Other people who are infected may have mild symptoms including fever, severe headaches, malaise, muscle pains, chills, and a rash. Nausea, vomiting, confusion, and joint pain may also occur. Symptoms usually improve on their own without treatment.