What is Ehrlichia ewingii, and how does it differ from other tick-borne diseases?

Ehrlichia ewingii is a bacterium transmitted through the bite of the lone star tick, Amblyomma americanum. It causes ehrlichiosis, a bacterial infection affecting white blood cells. Unlike Ehrlichia chaffeensis, the more commonly known cause of ehrlichiosis, Ehrlichia ewingii has been historically considered less prevalent. However, recent studies suggest a wider distribution and a higher percentage of cases than previously thought, challenging prior assumptions about its impact.

What are the common symptoms of an Ehrlichia ewingii infection, and how soon after a tick bite do they appear?

Symptoms of Ehrlichia ewingii infection typically appear within 1-2 weeks after a tick bite. Common symptoms include fever, headache, muscle aches (myalgia), malaise, thrombocytopenia (decreased platelets), and leukopenia (decreased white blood cells). Some individuals may also experience nausea, vomiting, diarrhea, or a rash. These symptoms are often similar to those of other illnesses, making early diagnosis important.

What regions are most affected by Ehrlichia ewingii, and has its geographic distribution changed recently?

Ehrlichia ewingii is primarily spread by the lone star tick, common in the eastern and southeastern United States. Recent studies indicate an expanding geographic range, with cases now identified in states like New Jersey and Indiana, where the disease was previously considered rare. This suggests that the risk of exposure to Ehrlichia ewingii might be more widespread than previously understood.

How is Ehrlichia ewingii diagnosed and treated, and what are the potential complications if left untreated?

Diagnosis of Ehrlichia ewingii involves recognizing symptoms and potentially undergoing blood tests to detect the presence of the bacteria. Treatment typically involves antibiotics. If left untreated, ehrlichiosis caused by Ehrlichia ewingii can lead to more severe complications, particularly in individuals with weakened immune systems. Therefore, early diagnosis and treatment are crucial for a full recovery.

What preventative measures can be taken to reduce the risk of contracting Ehrlichia ewingii, and why are these steps important?

Preventative measures to reduce the risk of contracting Ehrlichia ewingii include wearing long sleeves and pants, using insect repellent containing DEET, and performing thorough tick checks on yourself, your children, and your pets, especially when spending time outdoors in wooded or grassy areas. The increasing prevalence and expanding geographic range of Ehrlichia ewingii emphasize the importance of these preventive steps, as they are crucial for avoiding tick bites and reducing the risk of infection.

Lone star tick over a map of the US, symbolizing the spread of Ehrlichia ewingii.

Tick-Borne Diseases: Are You at Risk? Understanding Ehrlichia ewingii and Its Expanding Reach

Lena Voss in Health & Wellness December 2025 • 4 min read.

"New research reveals a higher prevalence of Ehrlichia ewingii infections, challenging previous assumptions about its geographic distribution and potential dangers."

Ehrlichiosis, a bacterial infection transmitted through tick bites, is a growing concern in the United States. While Ehrlichia chaffeensis has been recognized as the primary culprit, recent studies highlight the increasing presence and wider distribution of another species: Ehrlichia ewingii. This lesser-known bacterium is now appearing in regions where it was previously considered rare, prompting a reassessment of its potential impact on public health.

A recent study published in Emerging Infectious Diseases sheds light on this evolving situation. Researchers retrospectively analyzed data from an 18-month study of ehrlichiosis cases across the country. Their findings revealed that Ehrlichia ewingii was present in a significant percentage of cases, surpassing previous estimates. Even more surprising, the infection was identified in patients from New Jersey and Indiana, states not traditionally associated with this particular disease.

This discovery raises important questions about the true prevalence of Ehrlichia ewingii infections in the U.S. and underscores the need for greater awareness among healthcare providers and the public. Understanding the symptoms, risk factors, and diagnostic challenges associated with this emerging threat is crucial for timely diagnosis and effective treatment.

What is Ehrlichia ewingii and Why Should You Care?

Lone star tick over a map of the US, symbolizing the spread of Ehrlichia ewingii.

Ehrlichia ewingii is a type of bacteria that lives inside the cells of its host. It's primarily spread through the bite of the lone star tick (Amblyomma americanum), a common species found throughout the eastern and southeastern United States. The bacteria infect white blood cells, leading to a range of symptoms that can often be mistaken for other illnesses.

While Ehrlichia ewingii was first identified as a cause of human ehrlichiosis in the late 1990s, it has historically been considered less common than Ehrlichia chaffeensis. However, the recent study suggests this might not be the case. The researchers found that E. ewingii accounted for 9.2% of ehrlichiosis cases in their study, a significantly higher rate than previously reported nationwide.

Fever: Often the first and most common symptom.
Headache: Can range from mild to severe.
Muscle Aches (Myalgia): Pain and stiffness in muscles.
Malaise: A general feeling of discomfort, illness, or lack of well-being.
Thrombocytopenia: A decrease in platelets, which are essential for blood clotting. This can lead to easy bruising or bleeding.
Leukopenia: A decrease in white blood cells, which are crucial for fighting infection.

In some cases, people may also experience nausea, vomiting, diarrhea, or a rash. Symptoms typically appear within 1-2 weeks after a tick bite. If left untreated, ehrlichiosis can lead to more severe complications, particularly in individuals with weakened immune systems.

Staying Safe: Prevention and Actionable Steps

The increasing prevalence and expanding geographic range of Ehrlichia ewingii highlight the importance of taking preventive measures to avoid tick bites. When spending time outdoors, especially in wooded or grassy areas, remember to wear long sleeves and pants, use insect repellent containing DEET, and perform thorough tick checks on yourself, your children, and your pets. If you develop symptoms of ehrlichiosis after a tick bite, seek medical attention promptly. Early diagnosis and treatment with antibiotics are crucial for a full recovery.