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What is ehrlichiosis?

Ehrlichiosis ("air-lick-ee-oh-sus") is a tick-borne disease of white blood cells caused by very small bacteria. The bacteria invade white blood cells called "monocytes" and so ehrlichiosis is also called human monocytic ehrlichiosis (HME).

How is ehrlichiosis transmitted?

The bacteria that cause ehrlichiosis are carried by certain kinds of ticks and can be transmitted to a person when a tick bites them. In the U.S., the lone star tick (Amblyoma americanum) is known to carry and transmit the agent of ehrlichiosis. This tick does not occur in California.

How common is ehrlichiosis?

About 800 – 900 cases of ehrlichiosis are reported each year in the U. S. Ehrlichiosis does not occur in California because we do not have the tick species that transmits it. Most cases of HME occur in the eastern U.S., particularly in the south central U.S. Californians may be diagnosed with HME after exposure to areas where the tick vector occurs.

What are the symptoms of ehrlichiosis?

Most individuals infected with the bacteria that cause ehrlichiosis experience no or mild symptoms. When symptoms occur, they resemble influenza, with fever, headache, fatigue, muscle aches, and nausea. Some individuals may also have vomiting, cough, or a rash. More severe illness may occur in some patients, particularly elderly persons or those with weakened immune systems. The disease is rarely fatal (1% - 2% of cases).

How is ehrlichiosis treated?

Ehrlichiosis can be successfully treated with antibiotics. Persons with ehrlichiosis generally begin to feel better within one to two days of starting antibiotic treatment.

How do I know if I have ehrlichiosis?

If you experience flu-like symptoms within two to three weeks after receiving a tick bite, or after having been in an area where ticks are prevalent, consult your health care provider. Several different blood tests are available to your physician to help determine whether your illness is ehrlichiosis.

What can be done to prevent tick bites?

Taking appropriate precautions to avoid tick bites can reduce the risk of infection with ehrlichiosis, as well as other diseases transmitted by ticks.
  • Avoid areas where ticks are known to occur.
  • Use an EPA-registered repellent for use against ticks. Repellents with at least 20% DEET are effective and can be applied to the skin and clothing. Always follow directions on the container. 
  • Apply permethrin to clothing (only) to kill ticks. 
  • Thoroughly check yourself and others for ticks during and up to three days after activities in tick-infested areas. 
  • Shower soon after returning from tick habitat.
  • Before laundering, place clothing worn while in tick habitat in a hot dryer for 10 minutes to kill ticks crawling on clothing. 
  • Keep grass along trails, buildings, and camping areas mown.

How should attached ticks be removed?

Note: Prompt tick removal can prevent disease transmission. 
  •  Using tweezers, grasp the tick's mouthparts as close to the skin as possible. 
  • Gently pull the tick straight out, using a firm steady motion.
  • Wash your hands and the bite site with soap and water.
  • Apply an antiseptic to the bite site. 
  • See a healthcare provider if you develop any symptoms within 30 days of the tick bite.

Where can I find more information on ehrlichiosis?

The U.S. Centers for Disease Control and Prevention (CDC) has information available on their ehrlichiosis webpage. ​​
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