Anaplasmosis: Symptoms, Testing and Treatment

Quick answer

Anaplasmosis is a bacterial infection spread mainly by blacklegged ticks, most often reported in the Northeast and upper Midwest. Symptoms usually start 1 to 2 weeks after a bite: fever, chills, severe headache and muscle aches. CDC says doxycycline is the treatment of choice for all ages, and treatment should start as soon as anaplasmosis is suspected.

What is anaplasmosis?

Anaplasmosis is an infection caused by Anaplasma phagocytophilum, a bacterium spread mainly through tick bites. It is carried by the same ticks that spread Lyme disease: the blacklegged (deer) tick in the eastern U.S. and the western blacklegged tick along the West Coast. That is why it is one of the Lyme disease co-infections.

CDC says anaplasmosis is most commonly reported in the Northeastern and upper Midwestern states. The ticks that spread it usually live in woods and areas with high brush. The IDSA/AAN/ACR guideline notes that Anaplasma may be passed on within 24 hours of a tick attaching, sooner than Lyme bacteria typically are, so removing ticks quickly matters. See ticks that carry Lyme disease.

Anaplasmosis symptoms

Symptoms usually begin within 1 to 2 weeks after an infected tick bite. Many people don’t remember being bitten.

Early illness (days 1 to 5) is usually mild or moderate, CDC says, and can include:

• Fever and chills
• Severe headache
• Muscle aches
• Nausea, vomiting, diarrhea or loss of appetite

A rash is uncommon. CDC notes that a rash may be a sign of co-infection with Lyme disease or another tickborne illness. If you have a bull’s-eye or expanding rash, see our Lyme disease rash guide.

Later illness can be severe if treatment is delayed or if a person has other medical conditions. CDC lists respiratory failure, bleeding problems, organ failure and death among the possible complications, though severe disease is rare.

Who is at higher risk of severe illness

• People whose treatment is delayed
• Adults 65 and older (CDC’s clinician page also lists children under 5)
• People with weakened immune systems, such as those getting some cancer treatments, people with advanced HIV, organ transplant recipients, and people taking certain medicines

How anaplasmosis is diagnosed

CDC describes anaplasmosis as often a clinical diagnosis: your provider may start treatment based on symptoms and exposure, then confirm it later. Tests that may be used include:

• Blood counts and liver tests. Low white blood cells, low platelets and raised liver enzymes are common. Normal results early on do not rule it out.
• PCR on whole blood. CDC calls it the most accurate way to confirm anaplasmosis early. It works best in the first week and becomes less sensitive within 48 hours of starting antibiotics.
• Antibody tests (paired). The best evidence is a rise in antibodies between a sample taken in the first two weeks and a second one 2 to 10 weeks later. A single early test is often negative. Antibodies can stay high for months, and tests can cross-react with Ehrlichia.
• Blood smear. Clusters of bacteria (morulae) are sometimes seen in white blood cells in the first week, but this test is not sensitive enough to rely on alone.

Test results can take several weeks. Tell your provider about recent tick bites, gardening or hiking in brushy areas, and travel. CDC says not to rule out a tickborne infection just because you don’t remember a bite.

Anaplasmosis treatment

We don’t give doses; your provider decides on treatment. CDC’s guidance says:

• Doxycycline is the treatment of choice for patients of all ages, including children.
• Fever usually goes away within 24 to 48 hours. If you are not improving, CDC says the illness may not be anaplasmosis, so let your provider know.
• The course CDC describes is long enough to also cover possible Lyme bacteria picked up from the same tick.
• For people with a serious doxycycline allergy, or some pregnant patients with mild illness, other antibiotics may be considered with an infectious disease expert.
• CDC does not recommend antibiotics after a tick bite to prevent anaplasmosis.

Preventing anaplasmosis

There is no vaccine for anaplasmosis. CDC’s advice focuses on avoiding tick bites, controlling ticks on pets, and reducing ticks in your yard. Our Lyme disease prevention guide covers the same steps, since the same ticks are involved. Related infections: ehrlichiosis (a close relative, mostly from the lone star tick), babesiosis and spotted fever rickettsiosis. Compare tick species on our types of ticks page.

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