Ehrlichiosis and Lyme Disease: Symptoms and Treatment
Ehrlichiosis and Lyme disease can occur together after tick exposure, producing an acute illness with high fever, severe headache, and characteristic laboratory abnormalities.
The same environments that expose patients to Lyme disease may also involve ticks carrying Ehrlichia bacteria. When present, this coinfection can lead to a more acute and severe illness than expected with Lyme disease alone.
For a broader overview, see our coinfections hub.
What Is Ehrlichiosis?
Ehrlichiosis is caused by Ehrlichia species, primarily Ehrlichia chaffeensis and Ehrlichia ewingii in the United States. These organisms are transmitted by the lone star tick (Amblyomma americanum) and infect white blood cells.
The infection shares similarities with anaplasmosis, including acute febrile illness, laboratory abnormalities, and response to doxycycline. Differences in tick vectors and geographic distribution help distinguish the two.
In earlier clinical practice, infections now recognized as anaplasmosis were often grouped under ehrlichiosis, reflecting how terminology and classification have evolved over time.
This overlap in terminology contributes to ongoing confusion when comparing anaplasmosis and ehrlichiosis, as the two infections share clinical features but differ in epidemiology and vector patterns.
Ehrlichiosis Symptoms
Ehrlichiosis typically presents as an acute illness with rapid onset.
- High fever (often 102–104°F)
- Severe headache
- Muscle aches and fatigue
- Nausea or vomiting
- Confusion or altered mental status in severe cases
A rash may occur in some patients—more commonly in children—but is usually nonspecific and does not resemble the erythema migrans rash of Lyme disease.
For a broader overview of symptom patterns, see our Lyme disease symptoms guide.
Laboratory Findings
Laboratory abnormalities often provide important diagnostic clues.
- Low white blood cell count (leukopenia)
- Low platelet count (thrombocytopenia)
- Elevated liver enzymes
- Low sodium (hyponatremia)
The combination of acute fever and these laboratory findings in a patient with tick exposure should raise suspicion for ehrlichiosis.
These challenges reflect broader issues discussed in Lyme testing limitations.
Ehrlichiosis vs. Anaplasmosis
Ehrlichiosis and anaplasmosis have overlapping clinical presentations and similar treatment approaches.
Ehrlichiosis is more common in the southeastern and south-central United States, while anaplasmosis predominates in the Northeast and upper Midwest.
In practice, distinguishing between the two is often less important than recognizing either as a tick-borne bacterial infection requiring doxycycline.
Why Ehrlichiosis Is Often Missed
Ehrlichiosis is frequently mistaken for viral illness due to its acute onset, high fever, and systemic symptoms.
Diagnosis may also be missed when clinicians do not consider tick exposure or coinfection in patients who appear more systemically ill than expected.
Serology may be negative early, PCR testing is not always available, and blood smear identification can be insensitive. Because of these limitations, diagnosis often depends on recognizing clinical patterns rather than relying on a single test result.
Ehrlichiosis and Lyme Disease Coinfection
Although ehrlichiosis and Lyme disease are transmitted by different primary tick vectors, geographic overlap allows for coinfection.
In these cases, the acute symptoms of ehrlichiosis may overlap with or obscure Lyme disease, complicating diagnosis.
Other coinfections, such as Babesia, Bartonella, or Anaplasmosis, may also contribute to a more complex presentation.
Treatment and Complications
Ehrlichiosis typically responds quickly to doxycycline, with many patients improving within 24–48 hours.
Early treatment is important because delayed recognition can increase the risk of more severe illness.
Delayed treatment can lead to complications such as respiratory failure, kidney injury, neurologic complications, or bleeding disorders, though these are uncommon with prompt care.
When to Suspect Ehrlichiosis
Consider ehrlichiosis in patients with acute fever, tick exposure, and characteristic laboratory findings—especially in endemic areas.
When clinical suspicion is high, treatment with doxycycline is typically started while awaiting confirmatory testing.
Clinical Perspective
Ehrlichiosis is an acute tick-borne infection that may be overlooked when symptoms are attributed to viral illness.
Recognizing the combination of fever, leukopenia, and thrombocytopenia in a patient with possible tick exposure can help guide early diagnosis and treatment.
Patients may benefit from understanding coinfections, recognizing Lyme disease symptoms, and considering testing limitations when symptoms evolve rapidly.
Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.
Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention
