Ehrlichiosis: The Lone Star Tick's Signature Illness
Per the CDC, ehrlichiosis is the general name for diseases caused by Ehrlichia bacteria, spread primarily through the bite of infected ticks. Most reported cases come from E. chaffeensis, carried by the lone star tick. The CDC says early treatment can reduce the risk of severe illness; see a healthcare provider if you become ill after a tick bite.
What is ehrlichiosis?
Ehrlichiosis is the general name used to describe diseases caused in the United States by three bacteria: Ehrlichia chaffeensis, E. ewingii, or E. muris eauclairensis, according to the CDC. The agency notes that the majority of reported cases are due to infection with E. chaffeensis. These bacteria are spread to people primarily through the bite of infected ticks, including the lone star tick (Amblyomma americanum) and the blacklegged tick (Ixodes scapularis).
The New York State Department of Health adds a name you may see on lab paperwork: ehrlichiosis is also called human monocytic ehrlichiosis, or HME, and is spread to humans by lone star ticks infected with E. chaffeensis. The CDC also notes that in rare cases, Ehrlichia species have been spread through blood transfusion and organ transplant.
Which ticks carry ehrlichiosis?
It depends on the species of bacteria. Per the CDC, E. chaffeensis and E. ewingii are carried by the lone star tick, found primarily in the south-central and eastern United States. A CDC MMWR report makes the same point from another angle, describing E. chaffeensis and E. ewingii as disease agents known to be transmitted by the lone star tick. Since E. chaffeensis accounts for the majority of reported cases, the lone star tick has a fair claim to this disease as its signature.
The third species travels differently. Per the CDC, E. muris eauclairensis is carried by the blacklegged tick (Ixodes scapularis), and cases have only been reported from Wisconsin and Minnesota. The Minnesota Department of Health says people most likely get E. muris eauclairensis through the bite of an infected blacklegged tick, also called a deer tick. The department notes this species was first identified in 2009, and all patients described to date have reported likely blacklegged tick exposure in Minnesota or Wisconsin.
One detail from the CDC worth sitting with: tick bites can be painless, and many people do not remember being bitten.
What are the symptoms of ehrlichiosis?
People with ehrlichiosis will often have fever, chills, headache, muscle aches, and sometimes upset stomach, according to the CDC. Signs and symptoms typically begin within 1 to 2 weeks after the bite of an infected tick.
The CDC describes early signs and symptoms, meaning the first 5 days of illness, as usually mild or moderate. They may include fever, chills, severe headache, muscle aches, nausea, vomiting, diarrhea, loss of appetite, confusion, and rash.
The rash statistics come with careful scoping, so here they are exactly as the CDC frames them: up to 1 in 3 people with ehrlichiosis report a rash; rash is more common in people with E. chaffeensis ehrlichiosis and generally occurs more often in children than adults. The rash usually develops 5 days after fever begins, and it can look like red splotches or pinpoint dots.
The CDC's advice at this stage is plain: see your healthcare provider if you become ill after being bitten by a tick or after spending time in grassy, brushy, or wooded areas.
Why does early treatment matter?
Because the cost of waiting can be steep. Per the CDC, if antibiotic treatment is delayed, ehrlichiosis can sometimes cause severe illness, and early treatment can reduce the risk of developing severe illness. The agency lists severe, late-stage outcomes that can include damage to the brain or nervous system such as meningoencephalitis, respiratory failure, uncontrolled bleeding, organ failure, and death.
On treatment itself, we report what the agency says and nothing more. The CDC states that doxycycline is the treatment of choice for adults and children of all ages with ehrlichiosis, and that early treatment with the antibiotic doxycycline can prevent severe illness or death. CDC clinical guidance says doxycycline is most effective at preventing severe complications when it is started within the first week of illness, and that when ehrlichiosis is treated with doxycycline, fever "generally subsides" within 24 to 48 hours. The CDC advises speaking with a healthcare provider to learn about treatment for ehrlichiosis, and that conversation is the place for treatment decisions.
The Minnesota Department of Health puts it just as directly: ehrlichiosis is treated with antibiotics, and treatment should not be delayed if ehrlichiosis is suspected.
The CDC also flags who faces the highest risk of severe illness: people younger than 5 years old or older than 65, and people with weakened immune systems, such as those receiving some cancer treatments, individuals with advanced HIV infection, people who have received organ transplants, or people taking certain medications.
How common is ehrlichiosis, and where?
A 2016 study in the American Journal of Tropical Medicine and Hygiene analyzed national surveillance of E. chaffeensis ehrlichiosis from 2008 to 2012. It counted 4,613 reported cases, an incidence rate of 3.2 cases per million person-years. The severity figures from that same study are the reason this disease deserves respect: the hospitalization rate was 57%, the case fatality rate was 1%, and children under 5 had the highest case fatality rate at 4%. The study also recorded 55 cases of E. ewingii infection over the same period and noted that the overall reported rate of ehrlichiosis had increased 4-fold since 2000.
The climb has continued. In CDC national data combining anaplasmosis and ehrlichiosis, reported cases rose from 875 in 2004 to 5,750 in 2016, with 39,959 cases reported over that 13-year period.
On geography, the CDC's Vital Signs report describes ehrlichiosis, along with tularemia, as geographically widespread but more prevalent in the central United States. Per the CDC, ehrlichiosis caused by E. chaffeensis and E. ewingii is most frequently reported from the southeastern and south-central United States, from the East Coast extending westward to Texas. The Minnesota Department of Health describes the same pattern: human illness from E. chaffeensis and E. ewingii is most commonly reported from the southeastern and south-central United States, where the lone star tick is found. And the disease reaches farther north than many people expect. The New York State Department of Health reports that most New York cases have been reported on Long Island and in the Hudson Valley.
How does the CDC say to prevent tick bites?
There is no vaccine to prevent ehrlichiosis. The CDC says to prevent illness by preventing tick bites, preventing ticks on your pets, and preventing ticks in your yard. The agency calls reducing exposure to ticks the best defense against tickborne diseases, and notes that while tick exposure can occur year-round, ticks are most active during the warmer months, April through September. Our guide to tick season by region goes deeper on timing.
Know where to expect ticks. Per the CDC, ticks live in grassy, brushy, or wooded areas, or on animals, and many people get ticks in their own yard or neighborhood.
For personal protection, the CDC recommends:
- Using EPA-registered insect repellents containing DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol, or 2-undecanone.
- Treating clothing and gear with products containing 0.5% permethrin, which remains protective through several washings. Our permethrin plus picaridin system covers how treated clothing and skin repellents work together.
- Showering soon after being outdoors. Per the CDC, showering within two hours of coming indoors has been shown to reduce the risk of Lyme disease and may be effective in reducing the risk of other tickborne diseases.
- Conducting a full body tick check upon return from potentially tick-infested areas, including your own backyard.
A note on our own product, kept strictly to the label: Longsleeve is an EPA-registered picaridin lotion (EPA Reg. No. 101457-1). It repels mosquitoes and ticks for up to 14 hours. It is fragrance free, with nine disclosed ingredients.
Frequently asked questions
Can you get ehrlichiosis more than once?
Yes. The New York State Department of Health says that even if successfully treated, a person may become re-infected if bitten later by another infected tick.
Is ehrlichiosis contagious from person to person?
No. The New York State Department of Health states that ehrlichiosis is not spread from person to person.
How is ehrlichiosis diagnosed?
The Minnesota Department of Health says diagnosis is based on a history of exposure to tick habitat, a physical examination, and laboratory tests to confirm the diagnosis. If you think you were exposed, that is a conversation for your healthcare provider.
Does removing a tick quickly lower the risk?
Per the New York State Department of Health, if an attached tick is removed within 36 hours, the risk of ehrlichiosis infection is minimal. Our guide to safe tick removal covers the mechanics.
Last word, straight from the CDC: see your healthcare provider if you become ill after being bitten by a tick or spending time in grassy, brushy, or wooded areas. The agency's guidance keeps returning to the same point: an early conversation with a clinician.
Sources
- CDC, About Ehrlichiosis: https://www.cdc.gov/ehrlichiosis/about/index.html
- CDC, Signs and Symptoms of Ehrlichiosis: https://www.cdc.gov/ehrlichiosis/signs-symptoms/index.html
- CDC, Causes and Spread of Ehrlichiosis: https://www.cdc.gov/ehrlichiosis/causes/index.html
- CDC, Treatment of Ehrlichiosis: https://www.cdc.gov/ehrlichiosis/treatment/index.html
- CDC, Clinical Care of Ehrlichiosis: https://www.cdc.gov/ehrlichiosis/hcp/clinical-care/index.html
- CDC, Preventing Tick Bites: https://www.cdc.gov/ticks/prevention/index.html
- CDC, Morbidity and Mortality Weekly Report, Vital Signs, 2018: https://www.cdc.gov/mmwr/volumes/67/wr/mm6717e1.htm
- CDC, Morbidity and Mortality Weekly Report, 2023: https://www.cdc.gov/mmwr/volumes/72/wr/mm7230a2.htm
- New York State Department of Health, Ehrlichiosis Fact Sheet: https://www.health.ny.gov/diseases/communicable/ehrlichiosis/fact_sheet.htm
- Minnesota Department of Health, About Ehrlichiosis: https://www.health.state.mn.us/diseases/ehrlichiosis/basics.html
- American Journal of Tropical Medicine and Hygiene, 2016, national surveillance of ehrlichiosis 2008 to 2012: https://pmc.ncbi.nlm.nih.gov/articles/PMC4710445/
Last reviewed 2026-08-17 · every claim on this page is sourced above