Ehrlichiosis is a bacterial infection transmitted by the bite of a tick.
Human monocytic ehrlichiosis; HME; Human granulocytic ehrlichiosis; HGE; Human granulocytic anaplasmosis; HGA
Causes, incidence, and risk factors
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
The incubation period between the tick bite and when symptoms occur is about 7 - 14 days.
Symptoms may seem like the flu (influenza), and may include:
Other possible symptoms:
- Fine pinhead-sized areas of bleeding in the skin (petechial rash)
- Flat red rash (maculopapular rash) (uncommon)
- General ill feeling (malaise)
A rash appears in fewer than one-third of cases. Sometimes, the disease may be mistaken for Rocky Mountain spotted fever. The symptoms are often general, but patients are sometimes sick enough to see a doctor.
Signs and tests
The doctor will do a physical exam and check your vital signs, including:
- Blood pressure
- Heart rate
Other tests include:
- Complete blood count (CBC)
- Granulocyte stain
- Indirect fluorescent antibody test
- PCR testing of blood sample
Antibiotics (tetracycline or doxycycline) are used to treat the disease. Children should not take tetracycline by mouth until after all their permanent teeth have grown in, because it can permanently change the color of growing teeth. Doxycycline that is used for 2 weeks or less usually does not discolor a child's permanent teeth. Rifampin has also been used in patients who can not tolerate doxycycline.
Ehrlichiosis is rarely deadly. With antibiotics, patients usually improve within 24 - 48 hours. Recovery takes 3 weeks.
- Death (rare)
- Infection with the bacteria that cause Lyme disease
- Infection with the organism that causes babesiosis
- Kidney damage
- Lung damage
- Other organ damage
Calling your health care provider
Call your health care provider if you become sick after a recent tick bite or if you have been in areas where ticks are common. Be sure to tell your doctor about the tick exposure.
Ehrlichiosis is spread by tick bites. Preventing tick bites will prevent this, and other, tick-borne diseases. Common measures to prevent tick bites include:
- Avoiding dense brush and long grasses when hiking
- Checking yourself for ticks and removing any that you find after being outside
- Not standing under trees or bushes
- Using insect repellent
- Wearing clothing to cover skin
Studies suggest that a tick must be attached to your body for at least 24 hours to cause disease. Early removal will prevent infection.
If you are bitten by a tick, write down the date and time the bite happened. Bring this information, along with the tick (if possible), to your doctor if you become sick.
Dumler JS, Walker DH. Ehrlichia chaffeensis (human monocytotropic ehrlichiosis), anaplasma phagocytophilum (human granulocytotropic anaplasmosis), and other anaplasmataceae. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa : Churchill Livingstone Elsevier; 2009: chap 193.
Last reviewed 9/1/2013 by Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.
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