Anaplasmosis: What It Is, How It Spreads, and How It's Treated
Anaplasmosis is a bacterial illness spread to people through the bite of an infected blacklegged (deer) tick. It usually causes flu-like symptoms such as fever, chills, headache, and muscle aches, and it responds well to a common antibiotic (doxycycline) when treated early. It is most often reported in the Northeastern and upper Midwestern United States, with a smaller number of West Coast cases. Importantly, anaplasmosis is not spread by the Lone Star tick.
Last reviewed: 2026-07-20 · Educational only — not medical advice.
Not transmitted by the Lone Star tick. This illness is spread by Blacklegged tick (deer tick), Western blacklegged tick — a different tick. If a Lone Star tick bit you, this is generally not the concern.
What is anaplasmosis?
Anaplasmosis is an infection caused by the bacterium Anaplasma phagocytophilum. It belongs to the same family of tick-borne bacterial diseases as ehrlichiosis and behaves similarly. In the United States the bacteria are carried mainly by the blacklegged tick (Ixodes scapularis) in the eastern half of the country and, less commonly, by the western blacklegged tick (Ixodes pacificus) along the West Coast. These are the same ticks that can spread Lyme disease and babesiosis, so occasional co-infections happen. In rare cases, anaplasmosis has also been passed through blood transfusion. Most people who get anaplasmosis recover fully, especially when it is recognized and treated promptly. This page is for general education and is not medical advice.
Symptoms
Fever and chills
Severe headache
Muscle aches (myalgia)
Malaise and fatigue
Nausea, vomiting, or diarrhea
Loss of appetite
Cough (less common)
Laboratory findings a clinician may see: low white blood cell count (leukopenia), low platelets (thrombocytopenia), and mildly elevated liver enzymes
How soon do symptoms appear?
Symptoms typically begin about 5–14 days (roughly 1–2 weeks) after the bite of an infected tick. Many people do not remember being bitten.
Diagnosis
Anaplasmosis is diagnosed based on symptoms, possible tick exposure, and where you live or have traveled, supported by blood tests. Routine blood work may show low white-blood-cell and platelet counts and elevated liver enzymes, which can offer early clues. Confirmatory antibody tests may take days to weeks to become positive, so clinicians generally start treatment based on clinical suspicion rather than waiting for lab confirmation. A rash is not typical of anaplasmosis; if a rash is present, a clinician may consider co-infection with another tick-borne illness such as Lyme disease.
Treatment
Doxycycline is the recommended antibiotic for anaplasmosis in adults and children of all ages, and the CDC notes it is most effective when started early. Because early treatment can prevent severe illness, clinicians usually begin doxycycline as soon as anaplasmosis is suspected rather than waiting for test results. Alternative antibiotics are less effective. Most people improve within a day or two of starting the right antibiotic. Any decision about medication should be made with a healthcare provider.
Prevention
Prevention focuses on avoiding tick bites, since there is no vaccine. Use EPA-registered insect repellents (such as those containing DEET or picaridin), treat clothing and gear with permethrin, and stick to the center of trails to avoid brushy, wooded areas where ticks wait. After being outdoors, do a full-body tick check, shower within about two hours, and tumble dry clothes on high heat for at least 10 minutes to kill any ticks. Check pets regularly and talk with a veterinarian about tick control. Prompt, careful tick removal lowers the chance that a bite leads to illness.
Where it occurs
Anaplasmosis is most commonly reported in the Northeastern and upper Midwestern United States, matching the range of the blacklegged tick. A smaller number of cases occur along the West Coast, where the western blacklegged tick is the vector. Most infections are acquired in late spring and summer, with a peak around June and July. It is not a disease associated with the Lone Star tick's main range in the Southeast and South-Central states.
When to seek care: Contact a healthcare provider if you develop fever, chills, headache, or muscle aches within a few weeks of a tick bite or time spent in tick habitat—even if you never saw a tick. Let the provider know about any possible tick exposure, since early treatment works best. Seek prompt medical attention for warning signs such as trouble breathing, confusion, unusual bruising or bleeding, or symptoms that rapidly worsen. This information is educational and not a substitute for professional medical care. For emergencies such as trouble breathing or anaphylaxis, call emergency services. Educational information only — not medical advice. See our sources and disclaimer.
Anaplasmosis — frequently asked questions
Does the Lone Star tick cause anaplasmosis?+
No. Anaplasmosis is spread by blacklegged (deer) ticks in the East and western blacklegged ticks on the West Coast. The Lone Star tick is not a recognized vector of anaplasmosis; it is instead linked to ehrlichiosis, STARI, Heartland and Bourbon viruses, tularemia, and alpha-gal syndrome.
How soon do symptoms appear after a tick bite?+
Usually about 5–14 days (roughly 1–2 weeks) later, though many people never notice the bite. If flu-like symptoms follow possible tick exposure, mention it to your healthcare provider.
Is anaplasmosis the same as ehrlichiosis?+
They are closely related tick-borne bacterial diseases with similar symptoms and the same antibiotic treatment, but they are caused by different bacteria and carried by different ticks. Anaplasmosis is caused by Anaplasma phagocytophilum via blacklegged ticks; ehrlichiosis is caused by Ehrlichia species, often via the Lone Star tick.
How serious is anaplasmosis?+
Most cases are mild to moderate and respond well to early antibiotic treatment. Severe illness—including respiratory, bleeding, or organ problems—can occur, especially when treatment is delayed or in people with weakened immune systems, which is why prompt care matters.
Is there a vaccine for anaplasmosis?+
No. There is no vaccine, so preventing tick bites is the best protection—use repellent, treat clothing with permethrin, and check for ticks after being outdoors.
Spread by blacklegged (deer) ticks — NOT the Lone Star tick. Early sign is often an expanding erythema migrans rash.
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Anaplasmosis: What It Is, How It Spreads, and How It's Treated
Anaplasmosis is a treatable bacterial tick-borne illness spread by blacklegged (deer) ticks, not Lone Star ticks. Learn the symptoms, onset window, and doxycycline treatment.
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