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Anaplasmosis

NCCID Disease Debriefs provide Canadian public health practitioners and clinicians with up-to-date reviews of essential information on prominent infectious diseases for Canadian public health practice. While not a formal literature review, information is gathered from key sources including the Public Health Agency of Canada (PHAC), the USA Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO) and peer reviewed literature.

This disease debrief was prepared by Madeleine Fisher. Questions, comments, and suggestions regarding this disease brief are most welcome and can be sent to nccid@manitoba.ca.

What are Disease Debriefs? To find out more about how information is collected, see our page dedicated to the Disease Debriefs.

Questions Addressed in this debrief:

  1. What are important characteristics of Anaplasmosis?
  2. What is happening with current outbreaks of Anaplasmosis?
  3. What is the current risk for Canadians from Anaplasmosis?
  4. What measures should be taken for a suspected Anaplasmosis case or contact?

What are important characteristics of Anaplasmosis?

Cause

Human granulocytic anaplasmosis (HGA, hereafter anaplasmosis), is a tick-borne infection caused by the gram-negative, obligate bacterium of neutrophils, Anaplasma phagocytophilum. In the 1930s, anaplasmosis was identified as a veterinary agent, affecting cattle and other ruminants; however, the veterinary disease is caused by a different strain, Anaplasma marginale. The first documented human case was identified in 1990; initially termed human granulocytic ehrlichiosis, it was renamed in 2003. As tick populations continue to grow and spread, prevalence rates of anaplasmosis in humans are increasing. Anaplasmosis is transmitted to humans primarily through bites from the blacklegged tick and the western blacklegged tick (Ixodes scapularis and I. pacificus, respectively), both of which also transmit the bacteria that causes Lyme disease, B. burgdorferi. These ticks are found throughout Canada, but predominantly in eastern and central Canada.

Signs and Symptoms

Anaplasmosis infections present with acute onset of fever, accompanied by one or more of the following symptoms or conditions: headache, malaise, myalgia, thrombocytopenia, leukopenia (initially attributed to lymphopenia in early infection) and elevated hepatic transaminases. Other less commonly observed symptoms are stiff neck, nausea, cough, anaemia, and increased serum creatine levels. The incubation period from tick bite to presenting with symptoms is between 5-21 days.

Tick bites are typically small and painless, causing many people to be unaware that they have been bitten. However, a small red bump, similar to the mark left from a mosquito bite, often appears.

Severity and Complications

In most cases, anaplasmosis is mild and self-limiting. Symptoms typically resolve within 30 days, even without treatment. However, more severe cases are observed in certain populations, such as older patients and individuals with compromised immunity, as well as those in whom diagnosis and treatment are delayed.

Complications include septic or toxic-like shock syndrome, respiratory insufficiency, invasive opportunistic infections, rhabdomyolsis, pancarditis, acute renal failure, hemorrhage, and neurological conditions. The fatality rate ranges between 0.2 and 1.2%.

Epidemiology

General:

In Canada, the vectors for anaplasmosis are the Ixodes scapularis (black-legged), I. pacificus (western black-legged), and I spinipalpis (mouse) ticks. These hard-bodied ticks are not capable of persistently supporting Anaplasma phagocytophilum, so they are not reservoir hosts. Reservoir hosts include white-footed mice, deer mice, and white-tailed deer. The bacterium can be passed to humans by ticks at any stage of life: larvae, nymph, or adult.

The typical time required for transmission between ticks and humans is 24 to 48 hours; however, a small number of infected nymphs were found to transmit the bacteria in less than 24 hours. Transmission occurs predominantly via ticks, but it has also been documented through direct handling of infected reservoirs (i.e., white-tailed deer), blood and bone marrow transfusion, and organ transplant. Transmission from non-vector animals, such as household pets, and human to human transmission has yet to be documented. 

In Canada, Manitoba is the only province where anaplasmosis is reportable, and there is limited information on the occurrence rates of infected ticks. However, established blacklegged tick populations have been identified in Nova Scotia, New Brunswick, southern Quebec, eastern, southwestern and northwestern Ontario, and southern Manitoba. The risk of contracting anaplasmosis increases in proportion to the size of the tick population. High Lyme disease risk areas carry the highest risk of anaplasmosis.

Infection can occur at any time of year, although the peak period is in the warmer months from April to September. In Manitoba, the highest risk period is from May to July, when nymphal blacklegged ticks are active. There is a second, smaller peak in October and November when adult blacklegged ticks are most active.  

The incubation period for anaplasmosis ranges between 5 to 21 days. Most symptomatic patients who can recall a tick bite report this bite to have occurred between 7 to 14 days prior to symptom onset.

Clinical and Laboratory Diagnosis:

Early recognition is important in preventing severe illness. Anaplasmosis should be treated based on clinical suspicion; antibiotic treatment should not be delayed pending the results of a laboratory test.

A thorough history should be taken to determine if the patient has had a recent tick bite, exposure to wooded or brushy areas, or had travelled to areas where anaplasmosis is prevalent. If anaplasmosis is suspected based on this history and the signs and symptoms previously listed, treatment should not be delayed while awaiting confirmatory test results. It is not possible to determine whether the illness will be self-limiting in every patient, so all patients demonstrating symptoms should receive treatment.  

There are multiple diagnostic tests available for anaplasmosis, including PCR amplification, serology testing, antibody testing, blood-smear microscopy, and IHC and culture testing. The optimal test depends on the timing of the illness. PCR amplification is most sensitive in the first week of illness, with sensitivity rapidly decreasing after administration of antibiotics. Serology and antibody testing requires two tests, taken 2-4 weeks apart; and it is often negative in the first week of illness. Blood smear testing cannot be solely relied upon as it is relatively insensitive compared to the other tests. Lastly, culture isolations can only be conducted in specialized laboratories; routine hospital cultures cannot detect the organism. False negative test results can occur in the first 7-10 days of illness; healthcare practitioners should not rule out negative tests that occur within this period, but instead administer treatment based on clinical symptoms. Blood test results showing low platelet count, low white blood cell count, or elevated liver enzymes may also be indicative of infection.

Prevention and Control

Avoiding tick bites is the primary means of prevention for anaplasmosis. Education about the risk of tick-borne illnesses, personal protection measures, and what to do when bitten by a tick will all aid in minimizing the number and severity of anaplasmosis cases.

Tips for spending time outdoors:

  • Know where to expect ticks
    • Ticks live in grassy, brushy, and wooded areas
    • Areas with high grass and leaf litter should be avoided
  • Check your clothing and body after spending time outside
  • Consider treating your clothing with permethrin before heading outside or purchasing permethrin-treated clothing and gear
  • Bathe/shower within two hours of coming indoors
  • Walk in the middle of trails
  • Wear full coverage clothing; tuck your shirt into your pants and your pants into your socks
  • Take measures to prevent ticks from entering the house via pets
  • Take measures to reduce ticks in your yard

If a tick is found attached to the skin:

  1. Use tweezers to grasp the tick as close to the skin’s surface as possible
  2. Pull upward with one steady motion, avoid twisting or crushing the tick
  3. Cleanse the area with soap and water
  4. Mark your calendar for future reference

Vaccination

There is no vaccination for prevention of anaplasmosis in humans. At present there are no veterinary vaccines approved in Canada, although one is in use in the United States.

Treatment

There are multiple antibiotic treatments available including doxycycline, tetracycline, and rifampin. Doxycycline is currently the recommended first line treatment for adults and children of all ages. A failure to respond to treatment with 48 to 72 hours may indicate another tick-borne infection or a secondary opportunistic infection. Rifampin has shown to be an effective alternative to Doxycycline in patients who are allergic to Doxycycline.  

The majority of symptoms typically will resolve within 30 days of onset, even without antibiotic treatment. There have been no reports of active clinical illness persisting beyond 60 days. 

What is happening with current outbreaks?

The number of infections reported around the world have been steadily increasing since the first reported case of anaplasmosis in 1990. Ticks carrying Anaplasma phagocytophilum have been identified in North America, Europe, and Asia, with the highest incidence in North America. In the United States, the most recent data reported 5,655 annual cases in 2019.

What is the current risk for Canadians?

In Canada, the first locally recorded case occurred in 2009, in an Alberta resident. Manitoba is the only province in Canada that mandates reporting of anaplasmosis. Between the years 2015 and 2019, annual confirmed cases in Manitoba were 2, 11, 6, 14, and 4. In 2018, the first case of anaplasmosis in Ontario was detected.

Risk level across Canada is assumed to be relatively low but increasing. Risk is highest in areas with established vector populations, particularly Nova Scotia, New Brunswick, southern Quebec, eastern, southwestern, and northwestern Ontario and southern Manitoba.

What measures should be taken for a suspected case or contact?

Manitoba

Clinical cases are to be reported to Manitoba Health, Healthy Living and Seniors using the Tick-Borne Diseases Clinical Case Report form (link below) and submitted by fax to the Communicable Disease Control Unit.

Canada

There is no protocol for suspected cases in the other provinces and territories.