Ixodes scapularisAnaplasmosis is caused by a bacterium transmitted primarily by the bite of an infected blacklegged tick (Ixodes scapularis - see photo) or western blacklegged tick (Ixodes pacificus).

Most people infected with the bacteria develop fever and mild non-specific symptoms such as chills, headache and muscle aches. In most cases Anaplasmosis infection is mild, however older individuals and those with compromised immune systems may develop more severe illness and require hospitalization. Anaplasmosis infection can be successfully treated with antibiotics. Risk of infection can be lowered by preventing tick bites.

Image Content Provider: James Gathany US CDC PHIL


Anaplasmosis symptoms generally appear 5 – 21 days following the bite of an infected blacklegged tick. The first symptom is typically fever, followed by one or more of the common symptoms including chills, headache, muscle aches and joint pain. Older individuals and those with compromised immune systems may develop more severe illness with respiratory complications, opportunistic infections, neurological complications and kidney failure. Most cases are mild and self-limiting with all symptoms typically resolving within most patients within 30 days. However, those with severe illness often require hospitalization and fatalities are possible.

Blacklegged ticks can also transmit other infections, such as Babesiosis and Lyme disease. Co-infection with either of these may result in symptoms that are more severe and/ prolonged.


Anaplasmosis infection is caused by a bacterium, Anaplasma phagocytophilum. In North America Anaplasmosis infection normally cycles between small mammals, such as mice, and blacklegged ticks. Humans can become infected when bitten by an infected blacklegged tick. The highest risk period, May – July coincides with the peak activity of blacklegged tick nymphs.

Less common transmission methods of Anaplasmosis infection include mother to child, blood and/ or blood product transfusions and from handling infected animals (i.e. deer).


Antibiotic treatment is started based on a physician’s suspicion of infection. Fever typically resolves within 24 – 48 hours after treatment is started. Most symptoms resolve within 30 days of the onset of symptoms. For those with more severe symptoms the recovery period may be longer.


Restricting exposure to potentially infected blacklegged ticks is the key to preventing Anaplasmosis.

The risk of encountering potentially infected blacklegged ticks is greatest in blacklegged tick risk areas where surveillance has revealed established tick populations. Outside of these areas the likelihood of encountering blacklegged ticks is significantly lower. Blacklegged ticks are most commonly found in wooded or forested areas, or along the fringes of such areas, as these locations provide them with a suitable humid habitat in which to survive.

When active in these areas it is important to adopt preventative measures such as:

  • Use trails, whenever possible, and stay to the centre of hiking trails or paths,
  • Wear light coloured long pants and long sleeved shirts,
  • Tuck in clothing (pants and socks) to create a barrier,
  • Use an appropriate tick repellent.

Perform a thorough tick check after spending time outdoors inspect yourself, your children and your pets for blacklegged ticks and remove any found as soon as possible. Do not stop if you find one tick, as there may be more. Bathing soon after coming indoors is a good way to find any ticks. Be sure to check clothing and items such as backpacks which may have come into contact with vegetation as well. Finding and removing ticks in a timely manner can significantly reduce the likelihood of disease transmission.

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