People get ehrlichiosis from the bite of an infected tick. The deer tick also spreads Lyme disease and babesiosis. The disease is similar to Rocky Mountain spotted fever and can be severe and life-threatening. The most common symptoms are sudden high fever, tiredness, major muscle aches, severe headache, and, in some cases, a rash. Symptoms usually appear 3 to 16 days after a tick bite.
Diagnosis is difficult, even in severe cases.
Special laboratory tests can detect recent infection with Ehrlichia bacteria. Because diagnostic tests are not widely available, the diagnosis of ehrlichiosis is usually based on symptoms and a history of exposure to ticks. Anyone can get ehrlichiosis, although most cases have been in adults. The risk of severe illness and complications is probably highest in older persons. People who spend time outside in tick-infested areas during the spring and summer are also at increased risk for exposure.