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Tick-borne condition • Bacterial

Ehrlichiosis

Ehrlichiosis is a treatable bacterial illness spread to people mainly through the bite of an infected Lone Star tick. It usually causes fever, headache, and body aches that begin about 1-2 weeks after a bite, and it responds well to the antibiotic doxycycline when treatment starts early. Most people recover fully with prompt care; delayed treatment is what raises the risk of serious illness. This page is educational and is not medical advice — only a licensed clinician can diagnose or treat ehrlichiosis.

Last reviewed: 2026-07-20 · Educational only — not medical advice.

Carried by the Lone Star tick. Spread by: Lone Star tick, Blacklegged tick.

What is ehrlichiosis?

Ehrlichiosis is the general name for illness caused by the bacteria Ehrlichia chaffeensis, E. ewingii, or E. muris eauclairensis in the United States. In most of the country the Lone Star tick (Amblyomma americanum) spreads E. chaffeensis and E. ewingii; the blacklegged tick (Ixodes scapularis) spreads the less common E. muris eauclairensis in the upper Midwest. The bacteria infect certain white blood cells, producing a flu-like illness that ranges from mild to, if untreated, severe.

Symptoms

  • Fever and chills
  • Severe headache
  • Muscle aches and general fatigue or malaise
  • Nausea, vomiting, diarrhea, or loss of appetite
  • Confusion in more serious cases
  • Rash in roughly one-third of patients (more common in children than adults), often appearing about 5 days after fever begins

How soon do symptoms appear?

Symptoms usually begin about 1-2 weeks (roughly 5-14 days) after the bite of an infected tick, according to the CDC.

Diagnosis

A clinician diagnoses ehrlichiosis based on your symptoms, recent tick exposure, and where you live or traveled, supported by blood tests. Because laboratory confirmation can take days to weeks, providers often start antibiotics before results are back when they suspect a tick-borne infection. Routine blood work may show a low white blood cell or platelet count or elevated liver enzymes, which can support the diagnosis. It cannot be self-diagnosed.

Treatment

Doxycycline is the treatment of choice for adults and children of all ages, and it works best when started early — ideally within the first week of illness. The CDC advises that antibiotics should not be delayed while waiting for laboratory confirmation if ehrlichiosis is suspected. There is no vaccine. Any treatment decision should be made by a licensed clinician.

Prevention

There is no vaccine, so prevention centers on avoiding tick bites: use EPA-registered repellents (such as DEET or picaridin), treat clothing and gear with permethrin, avoid tall grass and leaf litter, walk in the center of trails, and do a full-body tick check after being outdoors. Removing an attached tick promptly with fine-tipped tweezers, pulling straight out with steady pressure, lowers your risk of tick-borne illness.

Where it occurs

Ehrlichiosis from E. chaffeensis and E. ewingii is reported most often from the southeastern and south-central United States, from the East Coast westward to Texas — matching the range of the Lone Star tick. The rarer E. muris eauclairensis form has so far been found only in Wisconsin and Minnesota, spread by the blacklegged tick.
When to seek care: Contact a healthcare provider promptly if you develop fever, severe headache, or body aches within a few weeks of a tick bite or time spent in tick habitat — especially in the southeastern or south-central US. Early antibiotic treatment greatly reduces the risk of severe illness. Seek urgent care for warning signs such as confusion, difficulty breathing, or unusual bleeding. Young children, adults over 65, and people with weakened immune systems are at higher risk for serious illness. For emergencies such as trouble breathing or anaphylaxis, call emergency services. Educational information only — not medical advice. See our sources and disclaimer.

Ehrlichiosis — frequently asked questions

Which tick spreads ehrlichiosis?+

In most of the US it is the Lone Star tick (Amblyomma americanum), which carries Ehrlichia chaffeensis and E. ewingii. In the upper Midwest, the blacklegged tick can spread the rarer E. muris eauclairensis. Note that the Lone Star tick does NOT spread Lyme disease.

Is ehrlichiosis the same as Lyme disease?+

No. They are caused by different bacteria and spread by different ticks. Lyme disease is spread by the blacklegged (deer) tick, not the Lone Star tick, and typically causes a spreading 'bull's-eye' rash — which is not a feature of ehrlichiosis.

How is ehrlichiosis treated?+

The antibiotic doxycycline is recommended for people of all ages, and it works best when started early. Clinicians often begin treatment based on symptoms before test results return. Treatment decisions should always be made by a licensed clinician.

How soon after a tick bite do symptoms start?+

Usually about 1-2 weeks (roughly 5-14 days) after the bite of an infected tick, per the CDC.

Does ehrlichiosis always cause a rash?+

No. Only about one-third of patients develop a rash, and it is more common in children than adults. The absence of a rash does not rule out ehrlichiosis, so don't wait for one to seek care.

Sources used

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Ehrlichiosis

Ehrlichiosis is a bacterial illness spread mainly by the Lone Star tick. Learn the symptoms, the ~1-2 week (5-14 day) onset window, how it's diagnosed and treated with doxycycline, and where it occurs in the US. Educational, not medical advice.

Educational • not medical advice
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