Ehrlichia chaffeensis andEhrlichia ewingii are transmitted by the lonestar tick in the southeastern and southcentral United States. In addition, a thirdEhrlichia species provisionally called Ehrlichia muris-like (EML) has been identified in a small number of patients residing in or traveling to Minnesota and Wisconsin; a tick vector for the EML organism has not yet been established. The symptoms caused by infection with these Ehrlichia species usually develop 1-2 weeks after being bitten by an infected tick. The tick bite is usually painless, and about half of the people who develop ehrlichiosis may not even remember being bitten by a tick.
Treatment: Doxycycline is the first line treatment for adults and children of all ages and should be initiated immediately whenever ehrlichiosis is suspected. Use of antibiotics other than doxycycline and other tetracyclines is associated with a higher risk of fatal outcome for some rickettsial infections.
Doxycycline is most effective at preventing severe complications from developing if it is started early in the course of disease. Therefore, treatment must be based on clinical suspicion alone and should always begin before laboratory results return. If the patient is treated within the first 5 days of the disease, fever generally subsides within 24-72 hours. In fact, failure to respond to doxycycline suggests that the patient?s condition might not be due to ehrlichiosis. Severely ill patients may require longer periods before their fever resolves. Resistance to doxcycline or relapses in symptoms after the completion of the recommended course have not been documented. Recommended Dosage Doxycycline is the first line treatment for adults and children of all ages: Adults: 100 mg every 12 hours Children under 45 kg (100 lbs): 2.2 mg/kg body weight given twice a day Patients should be treated for at least 3 days after the fever subsides and until there is evidence of clinical improvement.
Standard duration of treatment is 7 to 14 days. Some patients may continue to experience headache, weakness and malaise for weeks after adequate treatment. Statistics: E. ewingii infections are impossible to distinguish from E. chaffeensis infections based on clinical signs alone, and some proportion of cases currently reported as E. chaffeensis infection may actually be due to E. ewingii. There is no currently available serologic test that can distinguish these agents, and surveillance for E. ewingii is currently based on detection of the organism through molecular-based diagnostic tests. Beginning in 2008, a new separate reporting category was established for E. ewingii infection. A total of 28 cases of E. ewingii were reported to CDC from 2008?2010. Major research In 2009, an Ehrlichia species that appears to be closely related to Ehrlichia muris, and which has been provisionally called E. muris-like (or EML), was identified as a cause of human illness for the first time in the United States. Since its initial identification, at least six persons residing in Wisconsin and Minnesota have been confirmed with infection with the EML organism.