Human Granulocytic Anaplasmosis

Human granulocytic anaplasmosis (HGA; ICD-10 A79.2) is an emerging tick-borne infection caused by the bacterium Anaplasma phagocytophilum. Infection in humans occurs following a bite from the Ixodes scapularis tick (also known as the blacklegged or deer tick), which is the same type that can carry the pathogens causing Lyme disease, babesiosis, ehrlichiosis, Powassan virus disease. Though not as well-studied as Lyme disease, Anaplasma phagocytophilum may be transmitted after being attached for 24 hours, possibly as short as 12 hours (transmission of the etiologic agent of Lyme disease, Borrelia burgdorferi, requires the tick to be attached for at least 24-36 hours).

After an incubation of 5 to 21 days (usually 7 to 14 days), the infection typically presents with acute, undifferentiated fever, potentially with severe headache, malaise, myalgia, gastrointestinal symptoms, rash (<10%). Approximately 31% of infections are significant enough to warrant hospitalization and 3-7% of patients have life threatening complications including respiratory insufficiency, septic shock, disseminated intravascular coagulation, or renal failure.¹

• Reservoir: The mammalian hosts of A. phagocytophilum primarily include wild rodents (such as mice, rats, voles, etc.), but dogs and cats can become infected by consuming them. The Ixodes scapularis tick becomes a vector of A. phagocytophilum after feeding on these mammals.
• Modes of Transmission: Human infection can occur following a bite from an Ixodes scapularis tick. Excluding rare situations where A. phagocytophilum has been transmitted by blood transfusion² and a report of possible perinatal transmission,³ there is no person-to-person transmission. HGA has a seasonal occurrence with an incidence peak in June but continuing as long as November.¹
• Host Susceptibility and Resistance: Susceptibility is general. Infection with A. phagocytophilum is associated with outdoor activity, but there is evidence for transmission in suburban settings in the United States.^1,4,5 Importantly, up to 25% of patients with HGA will not recall a tick bite.

Blacklegged ticks in various stages of feeding:

Three nymphs of the blacklegged tick are shown in different stages of feeding.

The following image shows 5 female blacklegged ticks in different stages of feeding.

For additional photos showing blacklegged ticks in various phases of engorgement from feeding visit the Tick Encounter Resource Center website.

As climate change increases the distribution of Ixodes scapularis in Ontario, the incidence of tick-borne diseases has also increased. Ixodes scapularis ticks are present in Ottawa, and transmission of A. phagocytophilum has occurred. Regions surrounding Ottawa, including many locations where Ottawa residents visit for recreation, may also be considered risk areas for tick bites due to Ixodes scapularis. Note, however, that patients with anaplasmosis, as with other tick-borne infections, may not have noticed being bitten by a tick. At least 12 hours of attachment of a blood-feeding tick is usually required for transmission of the organism. Infrequent routes of transmission include blood transfusion, solid organ transplantation, direct contact with infected human or animal blood, inhalation of aerosol during butchering of infected host (e.g., deer carcass), and rare reports of perinatal transmission, the mechanism of which is yet to be established.

For the most current map at Lyme disease | Public Health Ontario, under “Type of Resource” click on “Surveillance Report” and look for most current year. This map can be used to extrapolate regions where Ixodes scapularis can be found. A recent tick-surveillance study (2011-2017) has identified regions where Anaplasma has been identified in captured ticks.⁶ A map of Ontario with a breakdown of Anaplasma-positive ticks by region, can be found at:

https://www.ajtmh.org/view/journals/tpmd/101/6/article-p1249.xml (Nelder MP, Russell CB, Lindsay LR, Dibernardo A, Brandon NC, Pritchard J, Johnson S, Cronin K, Patel SN. Recent Emergence of Anaplasma phagocytophilum in Ontario, Canada: Early Serological and Entomological Indicators. Am J Trop Med Hyg. 2019 Dec;101(6):1249-1258. doi: 10.4269/ajtmh.19-0166. PMID: 31628739; PMCID: PMC6896876).

For a Canadian risk map go to Lyme Disease Dashboard 2022, and for US data see Blacklegged Tick Surveillance | Ticks | CDC.

The incubation period of human granulocytic anaplasmosis (HGA) is between 5 and 21 days long (average 7 -14 days), and some infections may be asymptomatic. Common symptoms include fever (93%), headache (73%), myalgia (73%), and rigors (60%), with less common symptoms including nausea, vomiting, abdominal pain, anorexia, and cough (<30%). Rash is very infrequent and is more likely related to co-infection with Lyme disease. Lymphocytic meningoencephalitis is also very rare with HGA.

Serious complications include acute respiratory distress syndrome (ARDS), toxic shock syndrome-like illness, myocarditis, rhabdomyolysis, hemophagocytic lymphohistiocytosis (HLH), renal failure, demyelinating disorders, and opportunistic infections.

Laboratory findings include leukopenia (57-80%) with neutropenia, thrombocytopenia (38-93%), mild anemia (14-48%), neutrophilic inclusion bodies on blood smear (20-80%), and mild to severe elevation in hepatic transaminases (40-50%). Hyponatremia and elevated C-reactive protein are present in most cases. Disseminated intravascular coagulation has also been reported.

The diagnosis of human granulocytic anaplasmosis (HGA) can be challenging due to patients’ non-specific symptoms and delayed laboratory confirmation but should be suspected in cases of fever of unknown origin especially if there is a history of outdoor activities in a region where Ixodes scapularis is found. When Anaplasma is suspected, consultation with an infectious diseases specialist is recommended and treatment with doxycycline based on clinical signs and symptoms should be initiated before the diagnosis is confirmed (but not before blood specimens have been obtained to avoid compromising the sensitivity of the PCR assay).

Diagnosis of HGA can be achieved with the following tests:

• Complete Blood Count and Differential and Smear – notify your local hematopathologist or hematopathology technician of your suspicion for HGA, and they will review a blood smear for the presence of neutrophilic inclusions (morulae in granulocytes), which may be seen in HGA.

• Serologic Testing – Serology tends to become positive 1-2 weeks after the onset of illness, making it less useful for diagnosis in the acute setting. Turnaround time reported by Public Health Ontario Laboratory (PHOL) is up to 42 days from receipt of specimen by PHOL, as the samples are sent to the National Microbiology Laboratory (NML) in Winnipeg. Acute and convalescent serology should be done 2-4 weeks apart.⁷
  • A downloadable requisition form is available from the Public Health Ontario Laboratory’s website. Note, the request will be rejected unless a clinical and travel history is provided. 
• Blood PCR testing – Specimens are sent to the NML. This test is generally positive in the first 1-2 weeks of illness and is the most useful test in the acute setting.⁸ However, the turn-around time for this test tends to be about 21 days and so when there is sufficient clinical suspicion of HGA, treatment should be initiated prior to the confirmation of the diagnosis (but after specimen collection). 

Consideration may need to be given to testing for co-infection with other diseases carried by blacklegged ticks including Lyme disease, babesiosis, and Powassan virus disease.

For further information about human diagnostic testing, the following resources are available:

• Refer to the Public Health Ontario Laboratory Services webpage
• Contact the Public Health Ontario Laboratories

Suspected or confirmed cases of human granulocytic anaplasmosis are reportable to local public health under the Health Protection and Promotion Act.

Monday to Friday from 8:30 am to 4:30 pm: Call 613-580-2424, extension 24224 and leave a detailed, confidential message including your contact information; or fax 613-580-9640. 

After hours, on weekends, or holidays: Call 3-1-1 and ask to speak to Public Health on call. 

For more details on how to report, please visit Reporting a communicable disease. 

Prevention of tick bites is a cornerstone of human granulocytic anaplasmosis (HGA) prevention. There is no vaccine to prevent anaplasmosis. Patients are advised to adopt the following practices:

• Application of a Health Canada approved insect repellent containing DEET or icaridin to exposed skin and to clothing
• Wearing long pants, a long-sleeved shirt, shoes and socks to cover exposed skin
• Tucking pants into socks
• Wearing light coloured clothing so it is easier to spot ticks
• If possible, staying on the trails when hiking in the woods or walking in long grass

Performing a "full body" check (also on children, and pets if applicable) for ticks. Ticks often attach in areas such as between toes, behind knees, in the groin, armpits and scalp.

Suspected and confirmed cases of human granulocytic anaplasmosis are reportable to local public health under the Health Protection and Promotion Act.

For Provincial surveillance case definitions and disease-specific direction for the public health management of human granulocytic anaplasmosis, please see the Ontario Ministry of Health’s Appendix 1 - Case Definitions and Disease Specific Information. 

For more details on how to report, please visit Reporting a communicable disease. 

• Anaplasmosis, U.S. Centers for Disease Control and Prevention (CDC)
• Ehrlichiosis and anaplasmosis, Mayo Clinic

Lab Testing

• Lab Requisition form, Public Health Ontario
• Anaplasma (Anaplasma phagocytophilum) – Serology, Public Health Ontario Laboratory
• Tick Identification, Public Health Ontario (PHO will continue to accept ticks for identification from members of the public through health care providers.  Ottawa Public Health does not accept ticks for identification.)

General information on Anaplasma phagocytophilum

• Anaplasmosis Fact Sheet, Canada Food Inspection Agency
• Summary: Tick Species in Ontario (in English only), Public Health Ontario: This report brings together the scientific literature and surveillance information on ticks of Ontario into a single source. Explore the tick species reported from Ontario in the last 120 years, with information on their distribution, establishment status and medical and veterinary importance.
• Surveillance for Ixodes scapularis and Ixodes pacificus ticks and their associated pathogens in Canada, 2020, Canada Communicable Disease Report (CCDR). 
• Anaplasmosis, National Collaborating Centre for Infectious Diseases

International Resources on Anaplasma phagocytophilum 

• Anaplasmosis, U.S. Centers for Disease Control and Prevention (CDC)