- May 9, 2017
- HUMAN PARASITES
Babesiosis is a tickborne zoonotic disease that is caused by intraerythrocytic protozoa of the genus babesia. In the northeastern and upper midwestern regions of the United States, where Babesia microti is endemic, the incidence of babesiosis has increased dramatically in the past 10 years, particularly in New England.1,2 The severity of babesiosis varies from asymptomatic infection to life-threatening disease. The most common clinical presentation is a viral-like illness with fever and laboratory abnormalities including anemia.3 Risk factors for the development of severe babesiosis include older age, asplenia, immunodeficiency due to malignant or nonmalignant disease, human immunodeficiency virus (HIV) infection, and immunosuppressive therapy, such as B-cell depletion caused by rituximab.4-8
Patients with babesiosis frequently have clinical hemolysis. Intraerythrocytic protozoa replicate asexually and leave red cells to invade other erythrocytes by disrupting the cell membrane and lysing the cell.1 Non–immune-mediated hemolysis associated with babesiosis resolves with appropriate antimicrobial treatment and clearing of the parasitemia. Autoimmune hemolytic anemia, on the other hand, is caused by autoantibodies produced against the patient’s own erythrocytes, which leads to premature elimination of these cells from the circulation. Warm-antibody autoimmune hemolytic anemia (also known as warm autoimmune hemolytic anemia [WAHA]) is a type of anemia that is frequently seen in patients who have lymphoproliferative disorders or autoimmune conditions or who use certain medications.9
Autoimmune hemolytic anemia is associated with certain infections, including HIV8 and malaria.10There have been sporadic cases reported of immune hemolysis complicating babesiosis in patients with ongoing parasitemia or a history of autoimmune hemolysis.11-14 We present six cases of asplenic patients without previous autoimmune hemolytic anemia in whom WAHA developed 2 to 4 weeks after diagnosis of babesiosis despite antimicrobial treatment and resolution of B. microti parasitemia.
All the patients with a diagnosis of babesiosis who received care at Brigham and Women’s Hospital between January 1, 2009, and June 30, 2016, were identified through the hospital Research Patient Data Registry and a review of parasitology laboratory records. The Partners HealthCare Human Research Committee approved this study and waived the requirement for written informed consent.
Data on covariates of interest were extracted from the medical records, including patient demographic characteristics, underlying disease and coexisting conditions, level of B. microti parasitemia, antimicrobial treatment, transfusions of blood products, blood counts, and the results of blood-bank testing, including antibody screening, Coombs’ test (direct antiglobulin test), and antibody identification. We collected data on all hematologic complications and treatments that occurred in the ensuing 3 months after the diagnosis of babesiosis.
A warm autoantibody was identified if the following standard criteria were met: 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. Clinical and Laboratory Standards Institute recommendations were followed for assessment of parasitemia: thick and thin blood smears were evaluated by examination of a minimum of 300 oil-immersion fields per blood film to determine the presence of babesia parasites.
A total of 86 patients had a diagnosis of babesiosis during the 7.5-year period, with confirmation by blood smear or polymerase-chain-reaction (PCR) assay. Of the 86 patients, 18 were asplenic. Blood-bank testing was performed in 20 patients (23%) after the diagnosis of babesiosis, and 12 (14%) had direct antiglobulin tests performed. Nine of 12 direct antiglobulin tests were positive. Seven asplenic patients had warm autoantibodies identified, 6 of whom had clinical post-babesiosis WAHA and no alternative or additional explanations for clinical hemolysis.
The sentinel case involved a 43-year-old woman who had undergone splenectomy for Hodgkin’s lymphoma 15 years before the onset of babesiosis. She was hospitalized in 2009 with low-grade fevers and fatigue 2 weeks after receiving a tick bite. The level of B. microti parasitemia was 11%, and the hematocrit was 33%. Serologic tests for anaplasmosis, ehrlichiosis, and Lyme borreliosis were negative at that time. She was treated with azithromycin, atovaquone, and clindamycin. At discharge, the parasitemia level was 0.2% and the hematocrit was 34%. Four weeks after the diagnosis of babesiosis, the hematocrit declined to 25%, although no parasites were detected on smears. She had evidence of hemolysis with a lactate dehydrogenase (LDH) level of 773 U per liter, a reticulocyte count of 11%, and undetectable haptoglobin. Blood-bank testing was notable for a positive direct antiglobulin test for both IgG and complement component 3 (C3). A warm autoimmune antibody was identified. She received 4 weeks of prednisone treatment for WAHA, and antiparasitic treatment was continued for a total of 12 weeks because of uncertainty about the cause of her recrudescent hemolysis. The hemolysis resolved within 2 weeks after the initiation of prednisone.
Cases of Post-Babesiosis WAHA
Characteristics of the six cases of post-babesiosis WAHA are summarized in Patients had various underlying medical conditions but no history of autoimmunity. All had undergone splenectomy, five at least 1 year before presentation. B. microti was confirmed by PCR assay, and the parasitemia level ranged from 2.5% to 11.8%. All the patients had clinical and laboratory responses to antimicrobial treatment. All six patients were hospitalized for the initial management of babesiosis, and one required intensive care for the acute respiratory distress syndrome and intracranial hemorrhage. None of the six patients had evidence of coinfection with anaplasmosis, ehrlichiosis, or Lyme borreliosis.
At 2 to 4 weeks after diagnosis, acute anemia, characterized by an elevated mean corpuscular volume (MCV), reticulocytosis, an undetectable haptoglobin level, and an increased LDH level, developed in all six patients (Figure 1B). Although B. microti PCR tests remained positive in five of the six cases, parasitemia was undetectable on smears in all the cases. Direct antiglobulin tests for IgG and C3 were positive, eluates were panreactive (panagglutinins) without any antigen specificity, and a warm autoantibody was present. Only one patient had received a blood transfusion within 2 months before the development of WAHA. In one patient, idiopathic thrombocytopenic purpura developed in addition to WAHA (the Evans syndrome). The other five patients did not have additional autoimmune phenomena other than WAHA.
The severity of WAHA varied, as did the medical management of the condition. Four of the six patients required immunosuppressive treatment. Three patients received glucocorticoids alone for 3 to 6 weeks, and one patient received prednisone for 5 months and cyclophosphamide for 8 months. WAHA resolved within a few weeks without intervention in two patients. In the three cases in which blood-bank testing was repeated, the time to a negative direct antiglobulin test ranged from 10 days to 5.5 months.
An additional patient with a history of thalassemia major, previous splenectomy, and erythrocyte transfusions every 2 weeks had a weakly positive direct antiglobulin test result starting 4 weeks after the diagnosis of babesiosis, after the resolution of parasitemia on blood smear. A warm autoantibody was not identified until 11 weeks after babesiosis was diagnosed. Given the confounding factors of chronic hemolytic anemia and frequent transfusion requirements, the contribution of the warm autoantibody to her underlying clinical hemolysis could not be assessed; therefore, her case was not included among the cases of post-babesiosis WAHA.
Risk Factors for Post-Babesiosis WAHA
All the case patients had undergone splenectomy, as compared with 12 of the 80 patients in whom the syndrome did not develop (P<0.001 by Fisher’s exact test). No patient with post-babesiosis WAHA underwent exchange transfusion for the treatment of babesiosis, whereas 6 of the other 80 patients in the cohort did undergo transfusion (P=1.0); only 2 of the 18 splenectomized patients underwent exchange transfusion (P=0.74).
Persons who have undergone splenectomy are at higher risk for severe and relapsing babesiosis and, like other immunocompromised persons, typically receive longer courses of antiparasitic medications than otherwise healthy persons.7 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 post-babesiosis WAHA syndrome occurred in 7% of all the patients with babesiosis during the study period and in one third of asplenic patients. Although four patients required immunosuppressive treatment owing to the severity of their clinical hemolysis, there were no deaths as may occur in severe cases of autoimmune hemolytic anemia, especially when there are delays in the administration of immunosuppressive treatment or the transfusion of blood products.15
We have described here a clinical syndrome of post-babesiosis WAHA in patients without a history of immune-mediated hemolysis. Although the development of autoimmunity to red cells in asplenic patients with babesiosis has been noted previously in seven cases, there was ongoing parasitemia in five of these cases at the time of positivity on direct antiglobulin tests.11-14 In one of these cases, immune hemolysis developed in the context of transfusion-related alloantibodies.11 Two of the seven patients had a history of autoimmune hemolytic anemia before acquiring babesiosis and subsequently had the Evans syndrome.14 The cases in the current report are distinct in that WAHA developed despite the clearance of B. microti parasitemia, and none of the patients had a history of autoimmune hemolytic anemia. An asplenic patient recently received a diagnosis of post-babesiosis WAHA at Nantucket Cottage Hospital, Massachusetts, and has required immunosuppression with glucocorticoids and rituximab (Pearl D: personal communication). The infrequency of asplenia in the general population may explain why post-babesiosis WAHA had not been recognized previously in endemic areas.
We considered alternative explanations for WAHA in our patients, but none seemed plausible. Although Hodgkin’s lymphoma and acute myeloid leukemia are rarely associated with autoimmune hemolytic anemia, our two patients with these cancers were in remission at the time of presentation. The one patient in whom the syndrome developed 3 years after allogeneic stem-cell transplantation had a self-limited course without the need for immunosuppression, making a graft-versus-host disease–like phenomenon unlikely. Only one patient with the syndrome had received a transfusion in the 3 months before presentation, and no alloantibodies were detected. Drug-induced autoimmune hemolytic anemia is unlikely, because only one patient received quinine,16 and autoimmune hemolytic anemia has not been associated with atovaquone, azithromycin, or clindamycin.17 Although PCR testing for B. microti remained positive in five of the six cases at the time of the diagnosis of WAHA, there was no evidence of parasitemia on peripheral-blood smears. Microscopic examination of Giemsa-stained thick and thin blood smears has a detection limit of 10 to 100 parasites per microliter (0.0002 to 0.002% parasitemia), whereas PCR testing for B. microti lowers the limit of detection to 5 parasites per microliter (approximately 0.0001% parasitemia).18Such a low parasite burden cannot clinically explain the degree of hemolytic anemia that developed in these patients at the time of the diagnosis of WAHA.
A plausible mechanism for post-babesiosis WAHA in asplenic patients is immune-complex–mediated, or type III, hypersensitivity. In type III hypersensitivity, the antibody response to foreign antigens leads to the overproduction of immunoglobulins and increased amounts of insoluble immune complexes. These immune complexes are removed inefficiently by phagocytosis, particularly in asplenic patients, and can trigger the classical complement cascade and intense release of inflammatory mediators and subsequent lysis of red cells.19 In the absence of a spleen to maintain red-cell surfaces free of immune complexes, accumulation of these complexes may occur to a critical threshold, leading to clinically significant red-cell phagocytic clearance and complement-mediated destruction.19
An alternative explanation for the development of post-babesiosis WAHA is antibody-mediated, or type II, hypersensitivity, in which cross-reacting antibodies initially elicited against B. microti antigens that have been adsorbed onto red cells are subsequently elicited against similar human antigens. Splenectomy would facilitate the persistence of these erythrocytic surface antigens, which otherwise would be removed rapidly by the spleen, and the subsequent development of autoreactive antibodies. The time needed to stimulate and accumulate autoreactive antibodies may account for the delay of a few weeks that we observed for the development of WAHA after the initial diagnosis of babesiosis. A postinfectious delayed autoimmune hemolytic anemia has also been described with malaria,20 including in a few cases that occurred 1 to 4 weeks after the treatment of severe malaria with parenteral artesunate, by which time the patients had clinical improvement and resolution of parasitemia.21,22
The pathogenesis of post-babesiosis WAHA seems distinct from that of autoimmune hemolytic anemia in general. Splenectomy is a treatment for autoimmune hemolytic anemia, whereas in this syndrome, asplenia is a risk factor. In addition, in typical autoimmune hemolytic anemia, direct binding of antibody or complement to red-cell membranes leads to clearance by reticuloendothelial system cells rather than immune-complex deposition on the surface of red cells.23
In summary, the post-babesiosis WAHA syndrome can be a hematologic complication of babesiosis, and asplenic patients appear to be particularly at risk. 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. Post-babesiosis WAHA responds to immunosuppressive treatment rather than antiparasitic treatment. Understanding the activation of the immune response to babesiosis may elucidate the mechanisms of other causes of autoimmune hemolytic anemias.
Petz LD, Garratty G. Immune hemolytic anemias. 2nd ed. Philadelphia: Churchill Livingstone, 2004.
Janeway CA, Travers P, Walport M, Shlomchik M. Immunobiology: the immune system in health and disease. 5th ed. New York: Garland, 2001.
Sharma V, Samant R, Hegde A, Bhaja K. Autoimmune hemolysis in malaria: a report of three cases. J Assoc Physicians India 2012;60:129-131
Berentsen S, Sundic T. Red blood cell destruction in autoimmune hemolytic anemia: role of complement and potential new targets for therapy. Biomed Res Int 2015;2015:363278-363278
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From the Divisions of Infectious Diseases (A.E.W., M.W.M., K.D., S.V., J.H.M., F.M.M.), Transfusion Medicine (W.J.S.), and Hematology (M.O.A.), Brigham and Women’s Hospital, Harvard Medical School (A.E.W., M.W.M., W.J.S., M.O.A., J.H.M., F.M.M.), and Dana–Farber Cancer Institute (A.E.W., M.O.A., F.M.M.) — all in Boston.
Address reprint requests to Dr. Woolley at the Division of Infectious Diseases, Brigham and Women’s Hospital, 75 Francis St., Boston, MA 02115, or at email@example.com.