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Ehrlichiosis is a bacterial illness transmitted by ticks that causes flu-like symptoms. The signs and symptoms of ehrlichiosis range from mild body aches to severe fever and usually appear within a week or two of a tick bite. If treated quickly with appropriate antibiotics, ehrlichiosis generally improves within a few days.
Another tick-borne infection anaplasmosis is closely related to ehrlichiosis. But the two have distinct differences and are caused by different microorganisms.
The best way to prevent these infections is to avoid tick bites. Tick repellents, thorough body checks after being outside and proper removal of ticks give you the best chance of avoiding ehrlichiosis.
Symptoms of Ehrlichiosis
In the United States, the term “ehrlichiosis” may be broadly applied to several different infections. Ehrlichia chaffeensis and Ehrlichia ewingii are transmitted by the lonestar tick in the southeastern and southcentral United States. In addition, a third Ehrlichia 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.
The following is a list of symptoms commonly seen with this disease, however, it is important to note that the combination of symptoms varies greatly from person to person.
- Muscle pain
- Nausea / Vomiting / Diarrhea
- Conjunctival injection (red eyes)
- Rash (in up to 60% of children, less than 30% of adults)
Ehrlichiosis is a serious illness that can be fatal if not treated correctly, even in previously healthy people. Severe clinical presentations may include difficulty breathing, or bleeding disorders. The estimated case fatality rate (i.e. the proportion of persons who die as a result of their infection) is 1.8%. Patients who are treated early may recover quickly on outpatient medication, while those who experience a more severe course may require intravenous antibiotics, prolonged hospitalization or intensive care.
Causes of Ehrlichiosis
Ehrlichiosis is caused by bacteria that belong to the family called Rickettsiae. Rickettsial bacteria cause a number of serious diseases worldwide, including Rocky Mountain spotted fever and typhus. All of these diseases are spread to humans by a tick, flea, or mite bite.
Scientists first described ehrlichiosis in 1990. There are two types of the disease in the United States:
- Human monocytic ehrlichiosis (HME) is caused by the rickettsial bacteria Ehrlichia chaffeensis.
- Human granulocytic ehrlichiosis (HGE) is also called human granulocytic anaplasmosis (HGA). It is caused by the rickettsial bacteria called Anaplasma phagocytophilum.
Ehrlichia bacteria can be carried by the:
- American dog tick
- Deer tick (Ixodes scapularis) which can also cause Lyme disease
- Lone Star tick
In the United States, HME is found mainly in the southern central states and the Southeast. HGE is found mainly in the Northeast and upper Midwest.
Risk factors for ehrlichiosis include:
- Living near an area with a lot of ticks
- Owning a pet that may bring a tick home
- Walking or playing in high grasses
Treatment for Ehrlichiosis
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.
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.