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.


If a tick carrying the bacterium that causes ehrlichiosis has been feeding on you for at least 24 hours, the following flu-like signs and symptoms may appear — usually within seven to 14 days of the bite:

  • Mild fever
  • Headache
  • Chills
  • Muscle aches
  • Nausea
  • Vomiting
  • Diarrhea
  • Fatigue
  • Loss of appetite
  • Joint pain
  • Confusion
  • Rash
  • Cough

Some people infected with ehrlichiosis may have symptoms so mild that they never seek medical attention, and the body fights off the illness on its own. But untreated ehrlichiosis with persistent symptoms can result in an illness serious enough to require hospitalization.

When to see a doctor

It may take as long as 14 days after a tick bite for you to begin showing signs and symptoms of ehrlichiosis. If you get symptoms within two weeks of a tick bite, see your doctor.

If you experience any of the above symptoms soon after you've been in an area known to have ticks, see your doctor. Be sure to tell your doctor that you recently received a tick bite or visited an area with a high population of ticks.


Ehrlichiosis is caused by ehrlichia bacteria and is transmitted primarily by the Lone Star tick.

Ticks feed on blood, latching onto a host and feeding until they're swollen to many times their normal size. During feeding, ticks that carry disease-producing bacteria can transmit the bacteria to a healthy host. Or they may pick up bacteria themselves if the host, such as a white-tailed deer or a coyote, is infected.

Usually, to get ehrlichiosis, you must be bitten by an infected tick. The bacteria enter your skin through the bite and eventually make their way into your bloodstream.

Before bacteria can be transmitted, a tick must be attached and feeding for at least 24 hours. An attached tick with a swollen appearance may have been feeding long enough to have transmitted bacteria. Removing ticks as soon as possible may prevent infection.

It's also possible that ehrlichiosis may be transmitted through blood transfusions, from mother to fetus, and through direct contact with an infected, slaughtered animal.

Risk factors

Risk factors

Ehrlichiosis spreads when an infected tick, primarily the Lone Star tick, bites you and feeds on you for 24 hours or longer. The following factors may increase your risk of getting tick-borne infections:

  • Being outdoors in warm weather. Most cases of ehrlichiosis occur in the spring and summer months when populations of the Lone Star tick are at their peak, and people are outside more often.
  • Living in or visiting an area with a high tick population. You are at greater risk if you are in an area with a high Lone Star tick population. In the United States, Lone Star ticks are most common in southeastern, eastern and south-central states.
  • Being male. Ehrlichiosis infections are more common in males, possibly because of increased time outdoors for work and recreation.


Without prompt treatment, ehrlichiosis can have serious effects on an otherwise healthy adult or child.

People with weakened immune systems are at an even higher risk of more-serious and potentially life-threatening consequences. Serious complications of untreated infection include:

  • Kidney failure
  • Respiratory failure
  • Heart failure
  • Seizures
  • Coma


The best way to steer clear of ehrlichiosis is to avoid tick bites.

Most ticks attach themselves to your lower legs and feet as you walk or work in grassy, wooded areas or overgrown fields. After a tick attaches to your body, it usually crawls upward to find a location to burrow into your skin. You may find a tick on the back of your knees, groin, underarms, ears, back of your neck and elsewhere.

If you remove a tick in the first 24 hours after attachment, you reduce your risk of infection. While you may not be able to avoid going into areas where ticks are present, the following tips can make it easier to discover and remove ticks before they attach to your skin:

  • Wear light-colored clothing. Ticks are dark-colored. Light clothing helps you and others notice ticks on your clothing before they can attach themselves to your skin.
  • Avoid open-toed shoes or sandals. Ticks generally live in grassy areas or fields and can attach themselves to your feet and legs when you brush by. Wearing open-toed shoes or sandals increases the risk of a tick attaching to your bare skin and working its way under your clothes, out of sight from detection.
  • Apply repellent. Products containing DEET (Off! Deep Woods, Repel) or permethrin (Repel Permanone) often repel ticks. Permethrin is for use on clothing only. You can use DEET on your skin or clothing, but follow recommendations on the label.

    For children, use a DEET repellent containing less than 30 percent DEET, and use the product with caution. Don't use DEET on your or your children's hands or faces.

  • Wear long pants and a long-sleeved shirt. The less skin you expose, the less area a tick has to bite. For added protection, wear shirts, pants and socks with permethrin impregnated in the fabric.
  • Tuck your shirt into your pants and your pants into your socks. By doing this, ticks will be less able to crawl onto exposed skin. However, be aware that if ticks get on your clothing, they'll climb upward until they reach exposed skin. Check your clothing often while you're outdoors.
  • Stay on clear trails whenever possible. Ticks prefer grassy areas and may be less common on well-beaten paths.
  • Inspect your body. Do a complete visual inspection of your body. Be sure to check your head and neck because ticks will continue to climb upward until they find a suitable burrowing site. Use your hands to feel through your hair and in areas you can't see when you return from your outing or garden.

    Ticks can be as small as a strawberry seed, and they usually attach to hidden skin. Be sure to check all the possibilities. A shower alone will rarely dislodge attached ticks from your head and body.

  • Inspect your clothes and gear. Check your clothes, backpacks and other gear when you get home to look for ticks that hitched a ride. Spinning your clothes in the dryer for about an hour will kill any ticks you missed.
  • Don't forget your pets. Do a daily inspection for ticks on any pet that spends time outdoors.

Mayo medical institution Minute: Ways to avoid ticks

While you're enjoying a hike, ticks are looking for a ride.

"They get themselves in a position. And they will climb up the nearest object, like this blade of grass here." It's called questing. "It sticks out its legs, and that allows it to grab on to hosts as they walk by." You can lessen the chances you'll become a host. "Using insect repellents is a good idea."

Mayo medical institution parasitic diseases expert Dr. Bobbi Pritt suggests permethrin for your clothing and gear.

"You can really saturate your gear. Leave them out to dry, and, then, the next day, wear them."

Use permethrin on materials and DEET on skin. Spray the DEET repellent on exposed skin, including your legs and hands. Avoid your face, but be sure to protect your neck. Then, tuck your pants into your socks. And, on your hike, remember to avoid areas where those questing ticks may be perched.

"That's why you want to stay away from the tall grasses. Stay in the middle."

For the Mayo medical institution News Network, I'm Jeff Olsen.

July 13, 2019
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  3. Ferri FF. Ehrlichiosis and anaplasmosis. In: Ferri's Clinical Advisor 2016. Philadelphia, Pa.: Mosby Elsevier; 2016. https://www.clinicalkey.com. Accessed June 10, 2015.
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