The patient is a 61 year old male in good health until about 4 weeks prior to presentation when he sustained a tick bite on his left arm. He subsequently developed chills, fatigue, loss of appetite, and weight loss. Concerned that his symptoms were not improving, the patient presented to urgent care and a CBC was ordered. His CBC was remarkable for mild anemia (RBC count 3.96, HB 12.9) and thrombocytopenia (platelet count 78,000/cmm). Review of the peripheral blood smear revealed organisms present within his neutrophils. Given his history of a tick bite, Doxycycline was initiated for 14 days with immediate improvement of his symptoms, including a notable increase in appetite over the next few days.
Within the neutrophils are purple organisms distinct from the nuclei identified as morulae. PCR testing for Anaplasma confirmed the result.
Anaplasmosis is a disease caused by the bacterium Anaplasma phagocytophilum, previously known as Ehrlichia phagocytophilum causing human granulocytic ehrlichiosis (HGE). A taxonomic change in 2001 identified that this organism belonged to the genus Anaplasma, and resulted in a change in the name of the disease to Anaplasmosis (1). These bacteria are obligate intracellular organisms in the Rickettsia family (1,2). Anaplasma cannot survive outside the cell and once it has been released, it rapidly induces uptake signals in other host cells (3). The number of Anaplasmosis cases reported to CDC has increased steadily since the disease became reportable, from 348 cases in 2000, to 5,762 in 2017(1).
Anaplasmosis is spread to people by tick bites primarily from the blacklegged tick (Ixodes scapularis) and the western black legged tick (Ixodes pacificus)(1,2). Anaplasmosis can be transmitted through blood transfusion and has been found in refrigerated blood more than a week after collection. Transfusion related infections have occurred from asymptomatic donors (1).
Signs and symptoms of Anaplasmosis typically begin within 1–2 weeks after the bite of an infected tick, which can be painless and often goes unnoticed. Early signs and symptoms (days 1-5) are usually mild or moderate and may include fever, chills, headache, muscle ache, nausea, vomiting, and lack of appetite (1,3). Rarely, if treatment is delayed or if there are other medical conditions present, Anaplasmosis can cause severe illness. Signs and symptoms of severe (late stage) illness can include respiratory failure, bleeding problems, organ failure, and death. Laboratory findings can include mild anemia, thrombocytopenia, leukopenia (characterized by relative and absolute lymphopenia and a left shift) and mild to moderate elevations in hepatic transaminases (1). Abnormal laboratory findings can appear in the first week of illness; however, normal laboratory findings do not rule out possible infection.
Co-infection with other tick borne illnesses such as Borrelia burgdorferi (Lyme disease), Babesia microti (Babesiosis), Ehrlichia muris eauclairensis (Erlichiosis), and Powassan virus can be seen so additional testing may be necessary in some patients. Methods for diagnosing Anaplasmosis include serology, molecular methods, and morphological identification. Though morphologic identification is extremely specific is lacks sensitivity making molecular methods such as PCR the diagnostic methods of choice (2). Treatment for most Rickettsial illnesses including Anaplasmosis are tetracyclines, especially doxycycline which is the drug of choice (1,3).
- Centers for Disease Control and Prevention: Anaplasmosis. https://www.cdc.gov/anaplasmosis/index.html
- Procop, Gary W., et al. Konemans Color Atlas and Textbook of Diagnostic Microbiology. 7th ed., Wolters Kluwer Health, 2017.
- Tille, Patricia M. Bailey & Scotts Diagnostic Microbiology. 13th ed., Elsevier, 2014.
-Casey Rankins, DO, is a 3rd year Anatomic and Clinical Pathology resident at the University of Vermont Medical Center.
-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Associate Professor at the University of Vermont.