About Anaplasmosis

Anaplasmosis is an illness spread by ticks. In Wisconsin, it is spread by the deer tick, also known as the black-legged tick.

Anaplasmosis is caused by the bacterium Anaplasma phagocytophilum.

Anyone can get anaplasmosis, but people who spend more time outdoors are at a higher risk of being bitten by an infected tick. Ticks can be found in areas with woods, brush, or tall grass. Ticks are most active from May to September, but it is important to use caution year-round.

Map of Anaplasmosis cases per 100,000 residents 2018

 How is anaplasmosis spread to humans?

Anaplasmosis is spread to humans through the bite of an infected deer tick.

Tick crawling on skin

  • A tick must be attached for at least 24 hours to spread anaplasmosis to a person. It is important to remove ticks as soon as they are found to prevent illness.
  • Most people are infected by immature ticks, called nymphs.
    • Nymphs are very small, about the size of a poppy seed. They are difficult to see, and most people may not feel their bite. This makes them harder to remove promptly.
    • Nymphs are most active during the spring and early summer.
  • Adult ticks also spread anaplasmosis.
    • Adults are much larger than nymphs, and are more likely to be found and removed before the bacteria are spread to the person. The image to the right shows an adult deer tick.
    • Adult ticks are most active during the cooler months in early spring and fall.
  • Ticks can attach to any part of the body but are often found in hard-to-see areas, such as:
    • Behind the knees
    • Armpits
    • Scalp
    • In and around the ears
    • Inside the belly button
    • Groin

Anaplasmosis is preventable and treatable. Visit our Tick Bite Prevention page to learn how to prevent tick bites, and how to properly remove a tick if you are bitten.

 What are the signs and symptoms of anaplasmosis?

Symptoms can show up one to two weeks after being bitten by an infected tick.

The following symptoms can be seen with anaplasmosis. However, it is important to keep in mind that few people will have all symptoms listed, and the combination of symptoms varies greatly depending on the person. Early signs and symptoms are usually mild. However, if antibiotic treatment is delayed, more severe symptoms can occur, but this is rare. It is important to get treatment as soon as possible to avoid more serious illness.

Early signs and symptoms:

  • Fever
  • Chills
  • Severe headache
  • Muscle aches
  • Tiredness
  • Nausea, vomiting, diarrhea

Late signs and symptoms:

  • Respiratory failure
  • Bleeding
  • Organ failure
  • Death

 How is anaplasmosis treated?

Anaplasmosis can be treated with antibiotics. Doxycycline is the antibiotic of choice for adults and children of all ages. Treatment should be started whenever anaplasmosis is suspected. Most people treated with oral antibiotics during the early stages of anaplasmosis recover completely.

It is important to get treatment as soon as possible after symptoms start. The following table shows current treatment recommendations from the Centers for Disease Control and Prevention (CDC) for anaplasmosis in adults and children.

Treatment for Anaplasmosis
Age Category Drug Dosage Maximum Duration, Days
Adults Doxycycline 100 mg, twice per day 100 mg/dose 7–14
Children under 45 kg (100 lbs) Doxycycline 2.2 mg/kg body weight, twice per day 100 mg/dose 7–14


Antibiotic treatment following a tick bite is not recommended to prevent anaplasmosis. There is no evidence this practice is effective, and this may only delay onset of disease. Instead, if you get bitten by a tick, be alert for symptoms listed above and call your doctor if fever or other symptoms develop.

 Resources

DHS resources
CDC resources
Partner resources
Anaplasmosis is preventable and treatable. Visit our Tick Bite Prevention page to learn how to protect yourself from illnesses spread by ticks.

Questions about illnesses spread by ticks? Contact us!
Phone: 608-267-9003 | Fax: 608-261-4976

Last Revised: September 27, 2021