Ehrlichiosis is an infectious disease transmitted by the bite of a tick.

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, and have identified two types in the United States:

• Human monocytic ehrlichiosis (HME) is caused by the rickettsial bacteria called Ehrlichia chaffeensis.
• Human granulocytic ehrlichiosis (HGE) is also called human granulocytic anaplasmosis (HGA). It is caused by the rickettsial bacteria called Anaplasma phagocytophilum (once called Ehrlichia equi or Ehrlichia phagocytophila).

Ehrlichia bacteria can be carried by the Lone Star tick, the American dog tick, and the deer tick, which can also cause Lyme disease.

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 time between the tick bite and when symptoms occur is about 7 - 9 days. This is called the incubation period.

Symptoms may seem like the flu (influenza), and may include:

• Chills
• Fever
• Headache
• Muscle aches
• Nausea

Other possible symptoms:

• Diarrhea
• Fine pinhead-sized areas of bleeding in the skin (petechial rash)
• Flat red rash (maculopapular rash)
• Malaise

A rash appears in less than half of the cases. Sometimes, the disease may be mistaken for Rocky Mountain spotted fever. The symptoms are often quite general, but patients are sometimes sick enough to see a doctor.

The doctor will do a physical exam and check your vital signs, including:

• Blood pressure
• Heart rate
• Temperature

Other tests include:

• Complete blood count (CBC)
• Granulocyte stain
• Fluorescent antibody test

Antibiotics (tetracycline or doxycycline) are used to treat the disease. Young children should not take tetracycline by mouth until after all their permanent teeth have grown in, because it can permanently discolor growing teeth.

Ehrlichiosis is rarely deadly. With antibiotics, patients usually improve within 24 - 48 hours. Recovery takes 3 weeks.

• Death (rare)
• Kidney damage
• Lung damage
• Other organ damage

Call your health care provider if you become sick after a recent tick bite or if you've 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 condition, as well as other tick-borne diseases. Common measures 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 in order to cause disease, so early removal will prevent infection. If you are bit by a tick, write down the date and time the bite happened, and bring this information to your doctor if you become sick.

Bratton RL. Tick-borne disease. Am Fam Physician. 2005; 71(12): 2323-30.

Mandell GL, Bennett JE, Dolin R. Principles and Practice of Infectious Diseases. 5th ed. London: Churchill Livingstone; 2000:2310-2315.