Postbabesiosis Hemolytic Anemia: Asplenic Patients at Risk

Tara Haelle

March 09, 2017

Contracting the tick-borne parasitic disease babesiosis puts people at risk for warm autoimmune hemolytic anemia (WAHA) after the infection resolves, particularly if they are asplenic, a retrospective cohort study found. The patients who developed WAHA also lacked any history of autoimmunity.

"Although prolonged antimicrobial treatment may prevent relapsing babesiosis, the cases presented here show a unique syndrome of recrudescent clinical hemolysis 2 to 4 weeks after the initiation of antiparasitic treatment, in the absence of parasitemia on peripheral-blood smear," the authors write.

Ann E. Woolley, MD, from Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, and colleagues published their findings in the March 9 issue of the New England Journal of Medicine.

Babesiosis, caused by the intraerythrocytic protozoa Babesia microti, is mostly prevalent in the northeastern and upper midwestern regions of the United States, with rates increasing during the last decade, especially in New England. Individuals most susceptible to a severe babesiosis infection include older adults, patients with asplenia, those with HIV, those taking immunosuppressive therapy, and patients with disease-related immunodeficiency.

Although non-immune-mediated hemolysis is common during a babesiosis infection, it usually stops after the patient receives antibiotics and clears the parasite. WAHA, meanwhile, is typically seen in patients with autoimmune conditions or a lymphoproliferative disorder, but has been seen periodically in patients after recovery from babesiosis.

To explore the frequency of these cases, the researchers examined the medical records of the 86 patients seen at their center for babesiosis between January 2009 and June 2016. The researchers used the standard criteria to confirm presence of a warm autoantibody: "antibody screening was positive; all cells on the red-cell panel were reactive with patient plasma, including autologous red cells; the direct antiglobulin test was positive; and eluate from patient red cells reacted with all cells tested."

Six patients developed WAHA between 2 and 4 weeks after their babesiosis diagnosis, and all of them were among the 18 patients who were asplenic. The six patients would have already received antibiotics and would have cleared the parasite by the time they developed WAHA.

All six patients had warm autoantibodies and tested positive for direct antiglobulin tests for immunoglobulin G and complement component 3. "We considered alternative explanations for WAHA in our patients, but none seemed plausible," the authors write.

Although all the patients had some kind of preexisting condition, none had a history of autoimmune diseases or evidence of a concurrent infection with anaplasmosis, ehrlichiosis, or Lyme borreliosis. Only one of the six splenectomies had been performed in the previous year before babesiosis infection.

Four of the six patients received immunosuppressive treatment to treat the WAHA, three received glucocorticoids alone for 3 to 6 weeks, and one took prednisone for 5 months and cyclophosphamide for 8 months. Two patients did not require any treatment, and the WAHA resolved after a few weeks.

The researchers identified a history of splenectomy as a risk factor for postbabesiosis WAHA, as all six patients had one, and only 12 of the 80 patients who did not develop WAHA were asplenic.

"[T]he post-babesiosis WAHA syndrome can be a hematologic complication of babesiosis," the researchers write. "Immune-mediated hemolysis and screening for WAHA should be considered in patients with worsening or recrudescent hemolytic anemia after treatment of babesiosis, especially in asplenic patients." They note that immunosuppressive treatment, instead of antiparasitic therapy, adequately treats postbabesiosis WAHA.

No external funding was reported for the study. The authors have disclosed no relevant financial relationships.

N Engl J Med. 2017;376:939-946. Abstract

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