Anaplasmosis is a rare, tick-borne bacterial infection transmitted to humans by bites from blacklegged ticks. Illnesses are typically reported in the late summer and fall. There is no vaccine to protect people from anaplasmosis. Taking personal protection steps to prevent tick bites, such as using an EPA-registered repellent and dressing appropriately, is important. Effective treatments are available. In rare cases, a person may contract anaplasmosis from a blood transfusion.

Ticks That Carry Anaplasmosis

  • Blacklegged Tick
    Blacklegged Tick
    In the United States, anaplasmosis is carried primarily by the blacklegged tick found in the Northeast and Upper Midwest. This tick also transmits Lyme disease and can infect people with more than one disease at a time.
  • In rare instances, anaplasmosis has been reported along the Pacific Coast, eastern Oregon, western Utah, and Arizona where it is transmitted by the Western blacklegged tick.
  • The majority of cases occur during the summer when ticks are most active.
  • When an infected blacklegged or Western blacklegged tick bites a person, bacteria enter person’s the bloodstream and attack the red blood cells.
  • Generally, the tick must stay attached for 24 to 48 hours in order to transmit anaplasmosis, so removing a tick soon after a bite occurs can help prevent the likelihood of disease transmission.
  • Western Blacklegged Tick
    Western Blacklegged Tick
    Blacklegged tick bites are usually painless, and many people are unaware of their having been bitten.
  • Blacklegged ticks can carry more than one pathogen that can be transmitted to humans by the same bite (Lyme disease, anaplasmosis, babesiosis and others).


  • In 2018, there were approximately 4000 cases of anaplasmosis in the United States.
  • Deaths from anaplasmosis are rare
  • Health experts believe that cases of anaplasmosis are under-reported
  • Half of the individuals who experience symptoms require hospitalization

Where Anaplasmosis Is Found

Anaplasmosis is most frequently reported from the upper midwestern and northeastern United States with more than 70% of the cases occurring in five states: Massachusetts, Minnesota, New York, Pennsylvania, and Wisconsin.

Blacklegged tick territory has expanded in recent years, and cases of anaplasmosis have been reported more recently in Michigan and Virginia.

Anaplasmosis Incidence
Source: Centers for Disease Control and Prevention, National Notifiable Diseases Surveillance System


  • Usually occur 1–2 weeks after the bite of an infected tick
  • Most people will have mild or moderate illness, though severe illness and death have occurred
  • Symptoms will vary from person to person. Not all people will have the same symptoms

Early Symptoms (days 1-5) are usually mild or moderate and can include:

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

Late stage illness can include

  • Difficulty breathing/gasping for air
  • Excessive Bleeding
  • Heart, kidney, and/or liver failure
  • Brain-related issues such as confusion, seizures, or coma
  • Life-threatening internal infection
  • Death

Who Is Most at Risk?

Anaplasmosis is most often reported in

  • Males
  • Individuals over 40 years of age
  • People with weakened immune systems ( associated with cancer treatments, advanced HIV infection, prior organ transplants, or some medications)
  • People who live near or spend time in known tick habitats
  • Those who do not receive early treatment