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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. People who spend more time outdoors are at a higher risk of being bitten by an infected tick.

Ticks are commonly found in areas with woods, brush, or tall grass. Ticks are most active from May to November, but it’s important to use caution year-round.

Map of Anaplasmosis cases five year aggregate

Protect yourself with Tick Bite Prevention

Anaplasmosis 101

Tick crawling on skin

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

To prevent illness, it’s important to remove ticks as soon as you find them. A tick must be attached for at least 12–24 hours to spread anaplasmosis to a person.

Most people are infected by immature ticks, called nymphs. Nymphs are very small, about the size of a poppy seed. They’re hard to see. Most people don’t feel their bites. This makes them harder to remove right away. Nymphs are most active during the spring and early summer.

Adult ticks also spread anaplasmosis. Adults are larger than nymphs. They’re more likely to be found and removed before the bacteria 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. They often are found in hard-to-see areas, such as:

  • Behind the knees.
  • In the armpits.
  • On the scalp.
  • In and around the ears.
  • Inside the belly button.
  • On the groin.

Anaplasmosis is preventable and treatable. Learn about Tick Bite Prevention and how to properly remove a tick if you’re bitten.

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

The following symptoms can be seen with anaplasmosis. However, few people will have all the symptoms listed. The combination of symptoms varies for each person.

Early signs and symptoms are usually mild. However, more severe symptoms can occur if antibiotic treatment is delayed. Severe symptoms are rare, but it’s important to get treatment as soon as possible.

Early signs and symptoms:

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

Late signs and symptoms:

  • Respiratory failure
  • Bleeding
  • Organ failure
  • Death

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

It’s important to get treatment as soon as possible after symptoms start.

Treatment recommended by the CDC (Centers for Disease Control and Prevention)

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 isn’t recommended to prevent anaplasmosis. There is no evidence this practice is effective, and it may only delay onset of the disease. Instead, if you’re bitten by a tick, be alert for the symptoms listed above. Call a doctor if you develop a fever or other symptoms.

Resources from the CDC

Partner resources

  • Information from the University of Wisconsin-Madison Medical Entomology Laboratory—Wisconsin Ticks and Tick-borne Diseases
  • Information on ticks found in the Midwest, surveillance resources, and tick biology and development from the Midwest Center of Excellence for Vector-Borne Diseases—Ticks.

Contact us

Questions about illnesses spread by ticks? We’re here to help.

Bureau of Communicable Diseases
Phone: 608-267-9003
Fax: 608-261-4976

Last revised December 22, 2022