Version July 2025
INTRODUCTION —
Babesiosis is an infectious disease caused by protozoa of the genus Babesia. Babesia spp are transmitted primarily by tick vectors and rarely via blood transfusion, organ transplantation, or congenitally. Babesia protozoa invade and cause lysis of red blood cells in mammalian hosts [1-5].
Babesia microti is the primary agent of human babesiosis in the United States, particularly in the Northeast and upper Midwest where it is endemic. Most cases in Europe have been attributed to Babesia divergens, but the infection is sporadic. Babesiosis also occurs in China, where B. venatorum, B. microti, and B. crassa-like organism have been identified as human pathogens.
The treatment and prevention of babesiosis will be reviewed here. The microbiology, epidemiology, pathogenesis, clinical manifestations, and diagnosis of babesiosis are discussed separately. (See "Babesiosis: Clinical manifestations and diagnosis" and "Babesiosis: Microbiology, epidemiology, and pathogenesis".)
TREATMENT OF B. MICROTI INFECTION
Immunocompetent patients
Nonpregnant adults
Asymptomatic infection — Individuals with asymptomatic infection do not warrant treatment unless parasites are detected in blood for ≥1 month [1]. For patients with persistent parasitemia (≥1 month), we administer treatment.
Mild to moderate illness — Mild to moderate babesiosis typically occurs in immunocompetent patients and is associated with parasitemia <4 percent; it does not require hospital admission. (See "Babesiosis: Clinical manifestations and diagnosis", section on 'Mild to moderate disease'.)
●Treatment - Treatment with antimicrobial therapy is warranted for symptomatic individuals with mild to moderate B. microti infection confirmed by microscopy or polymerase chain reaction (PCR).
•Preferred regimen - The preferred regimen consists of azithromycin plus atovaquone given orally; dosing is summarized in the table (table 1) [1,2,5].
Adverse effects associated with atovaquone plus azithromycin include diarrhea and rash. Azithromycin can cause QTc prolongation and cardiac arrhythmias [6].
•Alternative regimen – An alternative regimen consists of clindamycin plus quinine given orally; dosing is summarized in the table (table 1) [1,2,5].
Adverse effects associated with clindamycin plus quinine included diarrhea, rash, and symptoms of cinchonism (e.g., tinnitus, decreased hearing, and vertigo), prompting dose reduction or drug discontinuation in one-third of cases. Quinine can cause QTc prolongation and cardiac arrhythmias [6].
•Duration - The duration of therapy is 7 to 10 days.
●Supporting evidence – Treatment with atovaquone plus azithromycin is supported by a randomized trial in which 58 adults with non–life-threatening babesiosis were treated with a seven day course of either atovaquone plus azithromycin (40 patients) or clindamycin plus quinine (18 patients) [7]. Three months after completion of therapy, no parasites were seen by microscopy and no Babesia deoxyribonucleic acid (DNA) was detected by endpoint PCR in any patient. Atovaquone plus azithromycin was associated with less frequent adverse effects than clindamycin plus quinine (15 versus 72 percent, respectively).
●Clinical response - Symptoms usually abate within 48 hours after initiating antimicrobial therapy and resolve within one to two weeks [4]. Fatigue may persist but generally resolves within three months after initiating therapy. Patients with mild to moderate babesiosis seldom experience complications. Data regarding the timeframe for resolution of anemia and other laboratory parameters are limited. No follow-up is required unless the patient has persistent or recurrent symptoms.
In immunocompetent patients who complete treatment for babesiosis and subsequently undergo splenectomy or become immunocompromised, an unexplained febrile illness should raise suspicion of babesiosis and prompt immediate clinical evaluation.
Severe illness — Severe babesiosis is associated with parasitemia ≥4 percent (although it can occur with parasitemia <4 percent) and may lead to complications, including end-organ impairment, persistent or relapsing disease, and/or death [8,9]. (See "Babesiosis: Clinical manifestations and diagnosis", section on 'Severe disease'.)
Management of severe babesiosis consists of hospitalization, antimicrobial therapy, and in some cases, red blood cell exchange transfusion.
Antimicrobial therapy
●Preferred approach
•Regimen - For treatment of severe babesiosis, we favor intravenous (IV) azithromycin plus oral atovaquone (table 1) [1,2,10]
•Duration - IV therapy can be replaced with oral therapy once symptoms have abated and parasitemia has been reduced.
The usual duration of therapy for immunocompetent patients with severe babesiosis is 7 to 10 days. The duration of therapy should be extended if parasitemia and symptoms, such as fever, persist. Cessation of therapy should be guided by parasite clearance and clinical improvement. Fatigue may persist for months following completion of a standard course of antibiotic therapy, but fatigue alone does not warrant extension of therapy [11].
•Supporting evidence - There have been no prospective trials to compare the efficacy of antimicrobial regimens in patients with life-threatening babesiosis. In a retrospective study of 40 patients hospitalized for severe babesiosis, some of whom experienced life-threatening disease, all but one improved on atovaquone plus azithromycin therapy and were discharged from the hospital [10].
●Alternative regimens – An alternative regimen for treatment of severe babesiosis consists of IV clindamycin plus oral quinine (table 1) [1,2,10].
The optimal approach for treatment of severe babesiosis when the above regimens are ineffective is uncertain. Based on case reports, alternative options include IV clindamycin plus oral atovaquone or a regimen consisting of azithromycin, atovaquone, and clindamycin [3,5,12].
Chloroquine is not effective for treatment of human B. microti infection [13]. In a hamster model of B. microti infection, other antimalarials (such as pyrimethamine, pyrimethamine-sulfadoxine, quinacrine, and sulfadiazine) have been ineffective [13,14]. In that model, primaquine has shown modest and transient activity [15].
Exchange transfusion — Management of red cell exchange transfusion should be handled in close consultation with experts in apheresis [8,16-18]. Exchange transfusion can be performed manually or using apheresis equipment [19].
●Indications
•Red blood cell exchange transfusion (ie, removing patient red blood cells and replacing with allogeneic red blood cells, either partially or completely) is recommended by the American Society for Apheresis and the Infectious Disease Society of America for patients with babesiosis and high-grade parasitemia (>10 percent) and/or one or more of the following: severe hemolytic anemia or severe organ (pulmonary, renal or hepatic) compromise [1,20]. Exchange transfusion early in the course of severe B. microti infection promptly reduces parasitemia and corrects anemia [8,12,16-19,21].
•Red blood cell transfusion is also indicated for patients who do not meet the above criteria but have hemoglobin level ≤7 g/dL or symptoms attributable to anemia (eg, hemodynamic compromise, dyspnea). (See "Indications and hemoglobin thresholds for RBC transfusion in adults" and "Red blood cell transfusion in infants and children: Indications".)
•Repeat exchange transfusion may be considered when parasitemia remains elevated following initial exchange transfusion [12,18,21-23].
●Supporting evidence - The use of exchange transfusion for management of babesiosis is based on a limited number of case reports and case series [8,18,21,24]. Two retrospective studies have examined the relationship between parasitemia and clinical outcome of B. microti infection. In one study including 19 patients who underwent red blood cell exchange, higher parasitemia just prior to exchange was associated with a longer hospital stay following exchange, but had no impact on one-month mortality [18]. In another study of 91 patients hospitalized for babesiosis, parasitemia was associated with changes in laboratory parameters that denote end-organ dysfunction [21]. These data support use of parasitemia >10 percent and/or end organ impairment as criteria for exchange transfusion in severe babesiosis. In Europe, mortality from B. divergens infection in immunocompromised patients has markedly decreased since prompt use of exchange transfusion (in conjunction with antimicrobial therapy) has been recommended [25,26].
Successful management of three patients with parasitemia >10 percent without exchange transfusion has been described [23]. A retrospective review of 32 babesiosis patients referred to an apheresis service for possible exchange transfusion found no difference in morbidity or mortality between the 23 patients who received exchange transfusion and the nine patients who were not exchanged [27]. In contrast, the death of a patient with peak parasitemia of 17 percent who did not receive exchange transfusion also has been reported [28].
Monitoring — For immunocompetent patients, we suggest monitoring parasitemia using peripheral blood smears during treatment of acute illness [1]. Monitoring parasitemia once symptoms have resolved is of limited value because immunocompetent patients almost never relapse. (See 'Mild to moderate illness' above and 'Severe illness' below.)
Recurrent infection — Management of reinfection in immunocompetent patients consists of a repeat standard course of atovaquone and azithromycin, unless antimicrobial resistance is documented [29].
Pregnant patients — During pregnancy, clindamycin plus quinine is the preferred regimen for treatment of B. microti infection; this combination crosses the placenta more readily than atovaquone and azithromycin [30,31]. Atovaquone plus azithromycin is an acceptable alternative regimen; successful use of this combination has been described in case reports [31].
Neither regimen has been associated with increased risk of congenital birth defects, stillbirth, or anemia [31].
Patients with splenic rupture — For patients with splenic rupture who are hemodynamically unstable or deteriorating rapidly, emergent splenectomy is warranted.
For patients who are hemodynamically stable with persistent hemorrhage, splenic artery embolization may be considered [32,33]. A nonsurgical approach is preferable if feasible; splenectomy impedes parasite clearance and predisposes to severe babesiosis in the case of re-infection [32].
Immunocompromised patients
Acute disease
Mild to moderate illness — Immunocompromised patients with mild to moderate B. microti illness are treated as outpatients with close monitoring. Antimicrobial therapy consists of oral azithromycin (500 mg orally per day) plus oral atovaquone (750 mg orally twice daily).
Laboratory parameters (complete blood count and parasitemia) should be monitored every two to three days until the blood count normalizes and parasites are no longer seen on smear.
The duration of therapy is 7 to 10 days. In some circumstances, a longer duration of therapy may be required. The total duration of therapy depends on individual clinical circumstances and should be tailored to resolution of symptoms and parasitemia, along with marked improvement of laboratory parameters (complete blood count, liver enzymes, renal function).
Immunocompromised patients should be advised to seek immediate medical attention if they develop fever or other symptoms consistent with babesiosis within a few days or weeks following apparent successful antibiotic therapy. A thin blood smear should be obtained for identification of Babesia parasites. (See "Babesiosis: Clinical manifestations and diagnosis", section on 'Microscopy'.)
Severe illness — Severe acute babesiosis typically occurs in patients with one or more of the following conditions: age >50 years, asplenia, malignancy, HIV/AIDS, or treatment with immunosuppressive drugs. (See "Babesiosis: Clinical manifestations and diagnosis", section on 'Severe disease'.)
These patients should be managed with hospital admission for administration of antimicrobial therapy and close monitoring. Exchange transfusion is warranted in some circumstances. (See 'Exchange transfusion' above.)
●Treatment regimen
•Preferred regimen – Antimicrobial therapy for immunocompromised patients with severe disease consists of IV azithromycin (500 mg/day) plus oral atovaquone (750 mg twice daily).
Once symptoms have abated and parasitemia has diminished, azithromycin can be given orally (500 mg per day), and oral atovaquone (750 mg twice daily) should be continued. Higher doses of oral azithromycin (up to 1000 mg per day) have been used and may accelerate parasite clearance [34-36].
•Alternative regimen – An alternative antimicrobial regimen is IV clindamycin (adult dose 600 mg IV every eight hours) plus oral quinine (adult dose 650 mg orally every eight hours). IV clindamycin can be replaced with oral clindamycin once symptoms have abated and parasitemia has been reduced.
●Monitoring – Laboratory parameters (complete blood count and parasitemia) should be monitored daily until parasitemia is <4 percent and symptoms have abated. Thereafter, parasitemia should be monitored every two to three days until parasites are no longer seen on smear. End-organ function should be closely monitored until it returns to normal [1]. PCR is more sensitive than blood smear and typically remains positive for months after clinical cure (complete resolution of symptoms with no recurrence) [11].
●Duration – Antimicrobial therapy should be continued for at least 7 to 10 days and until fever has resolved, other symptoms have resolved or markedly improved, and blood smears are negative.
Relapse disease — Severe acute disease followed by relapse typically occurs in patients who are highly immunocompromised [37]. These include patients with B cell lymphoma or other conditions treated with immunosuppressive regimens, particularly those that include rituximab or other B cell-depleting agents, patients with malignancy who also are asplenic, patients with solid organ or stem cell transplantation, and patients with HIV/AIDS. Relapse usually occurs within a few days or weeks after discontinuation of antibiotics, but the interval can be longer (see "Babesiosis: Clinical manifestations and diagnosis", section on 'Relapse').
●Management – The management of relapse consists of a repeat course of antibiotic therapy until cure is achieved. The level of immunosuppression should be reduced, if possible [34,38].
•Regimen selection – The antibiotic regimen used for relapse can be the same as that used for the initial course (usually azithromycin plus atovaquone) but for a longer duration. Patients who do not respond well to atovaquone and azithromycin therapy may be switched to clindamycin plus quinine. However, because quinine often is poorly tolerated, some physicians use a combination of atovaquone, azithromycin and clindamycin. Treatment failure has been observed with these regimens, and antimicrobial resistance for atovaquone, azithromycin, and clindamycin has been documented in immunocompromised hosts [35-37,39-41].
An alternative regimen consists of azithromycin, atovaquone, and atovaquone-proguanil. Dosing for atovaquone is 750 mg twice per day; atovaquone-proguanil is administered as a fixed combination tablet (atovaquone 250 mg and proguanil 100 mg) given as one or two tablets twice a day. To provide a total of 1500 mg atovaquone per day, additional atovaquone is given in the form of suspension.
Use of tafenoquine (300 mg on day 1, 150 mg on days 2 and 3, and then 300 mg weekly) has been reported for treatment of relapsing babesiosis [40,42]. Tafenoquine was combined with one of several different antimicrobial regimens, most commonly including atovaquone/proguanil. Maintenance therapy (consisting of tafenoquine alone or in combination was continued for one to six weeks after the first definitive negative B. microti PCR). G6PD status must be assessed before initiation of tafenoquine because it can cause severe drug-related hemolytic anemia in G6PD deficient patients. (See "Glucose-6-phosphate dehydrogenase (G6PD) deficiency".)
Other antibiotic combinations have been used successfully, but there have been few reports of their use. These include atovaquone, azithromycin, clindamycin, and quinine, or azithromycin plus quinine [1,5,37,43-46].
•Duration – The optimal duration of antibiotic treatment for relapsing babesiosis is unclear. In the original case series of relapsing babesiosis (when real-time PCR assays could not be ordered from commercial laboratories), management consisted of administering the antimicrobial regimen for at least six consecutive weeks, including two consecutive weeks during which Babesia parasites were no longer detected on blood smear. The median duration of antimicrobial therapy was about 3.5 months; the success rate was about 80 percent [34,36,37].
In a subsequent case series (for which real-time PCR was used to monitor low-grade infection) treatment was given for two weeks beyond the first negative B. microti PCR [40]. The median duration of antimicrobial therapy was about 2 months; the success rate was about 80 percent. Despite the sensitivity provided by real-time PCR, cases of relapse following apparent parasite clearance (both blood smear and PCR) have been described, emphasizing the need for close follow-up [39,47,48].
Co-infection with tick-transmitted pathogens — In the United States, Ixodes scapularis ticks transmit three frequently encountered human pathogens: Borrelia burgdorferi (Lyme disease), Anaplasma phagocytophilum (anaplasmosis), and Babesia microti (babesiosis). These ticks are also capable of transmitting other pathogens, including Borrelia mayonii (Lyme disease), Borrelia miyamotoi (hard tick relapsing fever), Powassan virus (Powassan virus disease), and Ehrlichia muris eauclairensis (ehrlichiosis).
Reported human coinfection rates differ because of differences in pathogen strains, differences in climate and geography, and differences in research methods (such as case definitions) [49-52]. Approximately half of patients with babesiosis are coinfected with Lyme disease, and most of these patients present with an erythema migrans rash [49-51,53-55]. The frequency of coinfection with anaplasmosis is much lower [51,54].
Patients with known or suspected babesiosis should be evaluated carefully for erythema migrans rash. Testing for Lyme disease and anaplasmosis is warranted in areas where these diseases are endemic and when clinical manifestations suggest anaplasmosis or Lyme disease.
In settings where Lyme disease and anaplasmosis are highly endemic, empiric treatment with doxycycline (for coinfection with Lyme disease and/or anaplasmosis) may be considered pending definitive diagnostic data regarding coinfection. For patients treated for babesiosis whose symptoms worsen or do not resolve within the first 48 hours of therapy, we suggest initiating empiric doxycycline therapy, pending laboratory diagnostic data. (See "Clinical manifestations of Lyme disease in adults" and "Diagnosis of Lyme disease" and "Human ehrlichiosis and anaplasmosis".)
TREATMENT OF INFECTION DUE TO OTHER SPECIES
B. crassa-like organisms — In a case series of 31 patients infected with B. crassa-like organisms in northeastern China, all experienced a mild to moderate illness [56]. None was treated with antimicrobial regimens recommended for babesiosis caused by B. microti; three patients received clindamycin alone. None of the patients died.
Two case reports from Europe indicate that B. crassa-like organisms can cause severe disease in immunocompromised patients [57,58]. Both patients were treated with oral clindamycin plus oral quinine. One was discharged after 6 days of therapy; the other required intensive care for shock but eventually recovered.
B. divergens — Clinical information about treatment of B. divergens infections is limited to case reports. Infection due to B. divergens frequently causes fulminant illness; therefore, illness attributed to this species should be considered a medical emergency and treated with a combination of antimicrobial therapy and exchange transfusion.
The antimicrobial regimen of choice has been intravenous (IV) clindamycin (in adults: 600 mg IV every 6 to 8 hours; in children: 7 to 10 mg/kg IV every 6 to 8 hours [maximum 600 mg/dose]) combined with oral quinine (in adults: 650 mg orally every 8 hours; in children: 8 mg/kg orally every 8 hours [maximum 650 mg/dose]). The duration of therapy is at least 7 to 10 days [1,59]. Other regimens have included clindamycin monotherapy and, in one case, IV pentamidine plus oral trimethoprim-sulfamethoxazole [25,60].
Following clearance of B. divergens parasitemia, anemia that is severe enough to warrant transfusion of red blood cells may persist for >1 month [25].
B. divergens-like organisms — Clinical experience with treatment of infection due to B. divergens–like organisms is limited to case reports [61-65]. Oral quinine or quinidine (650 mg three times daily) plus IV clindamycin (650 to 900 mg three times daily or 1200 mg twice daily) have been used. Quinidine is no longer available in the United States.
B. divergens-like organisms often cause severe disease in immunocompromised hosts, as reported in a patient with severe hemolytic anemia and multi-organ failure. Cure was achieved after pressor support, mechanical ventilation, renal replacement therapy, a double volume red blood cell exchange and five weeks of antimicrobial therapy consisting mostly of clindamycin, plus atovaquone plus azithromycin [65]. Another case described severe hemolytic anemia and multi-organ failure; a red cell exchange was performed and cure was achieved after a two week treatment with atovaquone plus azithromycin [66].
B. duncani — Clinical experience with treatment of infection due to B. duncani is limited [67-71]. All reported cases of B. duncani infection have been treated with a course of clindamycin (600 mg three to four times per day or 1200 mg twice daily) plus quinine (600 to 650 mg three times daily). In one case, symptoms relapsed and were successfully treated with IV clindamycin (1200 mg twice daily). In severe cases, red blood cell exchange transfusion and hemodialysis were instituted.
B. venatorum — Clinical experience with treatment of infection due to B. venatorum is derived from cases in Europe and China [72-76].
A mild case was cured with IV clindamycin (600 mg three times daily) [73]. A more severe case was treated successfully with IV clindamycin (600 mg three times daily) plus oral quinine (650 mg three times daily). Hemolytic anemia required the transfusion of 11 units of packed red blood cells [73]. Another severe case complicated by acute renal failure was successfully treated with oral clindamycin (600 mg three times daily) plus oral quinine (500 mg three times daily) [74].
A fourth case had received rituximab prior to the diagnosis of babesiosis and relapsed following a course of oral clindamycin plus oral quinine. Because of intolerance to quinine, the second course consisted of oral atovaquone (750 mg twice daily) plus oral azithromycin (500 mg once daily). Atovaquone was continued for five months to treat persistent parasitemia in the absence of symptoms [72].
A child from northwestern China experienced severe B. venatorum disease and was cured with a course of oral atovaquone (20 mg/kg twice daily) plus oral azithromycin (12 mg/kg once daily) [75]. In a case series of B. venatorum infection from northeastern China, 4 of 48 patients were treated with clindamycin alone; the other cases resolved despite receiving antibiotics that are not commonly used for babesiosis.
PREVENTION —
Prevention of babesiosis consists of personal protective measures that minimize exposure to ticks [3,5]. Patients at risk of severe babesiosis (asplenic individuals and other immunocompromised individuals) should avoid Babesia endemic areas during the tick transmission season (late spring, summer, and early fall), particularly those where ticks abound. (See "Prevention of Lyme disease", section on 'Personal protection'.)
If it is not possible to avoid such exposure, the risk of babesiosis can be reduced by wearing long pants and long-sleeved shirts, applying tick repellants to skin (such as N,N-diethyl-metatoluamide [DEET]) and clothing (Permethrin), and performing tick checks after possible exposure. (See "Prevention of arthropod bites: Repellents and other measures".)
Environmental management also may be helpful. Interventions include keeping lawns mown, placing stone or wood chip barriers between lawn and woods, spraying property with an acaricide, placing cotton balls impregnated with permethrin in yards where mice bring them to their nests, and culling the local deer herd.
There is no antibiotic regimen for prophylaxis of babesiosis. There is no vaccine available for human use.
SOCIETY GUIDELINE LINKS —
Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Tick-borne infections (including Lyme disease, ehrlichiosis, babesiosis, rickettsial infections, and others)".)
SUMMARY AND RECOMMENDATIONS
●Immunocompetent patients
•Mild to moderate illness – For immunocompetent individuals with mild to moderate Babesia microti illness, we suggest treating with oral azithromycin plus oral atovaquone (Grade 2C). Treatment is administered orally for 7 to 10 days. Dosing is summarized in the table (table 1). For individuals with asymptomatic B. microti infection, we suggest no antimicrobial therapy unless parasites are detected in blood for ≥1 month (Grade 2C). (See 'Mild to moderate illness' above and 'Asymptomatic infection' above.)
•Severe illness
-Antimicrobial therapy – For immunocompetent individuals with severe B. microti infection, we suggest treatment with intravenous (IV) azithromycin plus oral atovaquone (Grade 2C). An alternative regimen consists of intravenous clindamycin plus oral quinine (table 1) (see 'Severe illness' above).
The usual duration of antimicrobial therapy for immunocompetent patients with severe B. microti infection is 7 to 10 days. In some circumstances, a longer duration of therapy may be needed. Intravenous therapy can be replaced with oral therapy once symptoms have abated and parasitemia has been reduced. (See 'Antimicrobial therapy' above.)
-Exchange transfusion – Patients with severe B. microti infection may warrant exchange transfusion. We suggest exchange transfusion for patients with high-grade parasitemia (>10 percent), severe hemolytic anemia, or end-organ (eg, pulmonary, renal, or liver) impairment (Grade 2C). (See 'Exchange transfusion' above.)
●Immunocompromised patients
•Acute disease
-Mild to moderate illness – For immunocompromised patients with mild to moderate B. microti illness, we suggest initial treatment with oral azithromycin plus oral atovaquone (Grade 2C) as well as close monitoring. The duration of therapy is 7 to 10 days; in some circumstances, a longer duration may be required. The total duration depends on individual clinical circumstances and should be tailored to resolution of symptoms and improvement of laboratory parameters including parasitemia. For patients who do not improve within 48 hours, we hospitalize and treat as for severe illness. (See 'Mild to moderate illness' above.)
-Severe illness – Immunocompromised patients with severe B. microti infection should be managed with hospital admission. We suggest treatment with IV azithromycin plus oral atovaquone (Grade 2C); IV clindamycin plus oral quinine is an alternative regimen. (See 'Severe illness' above.)
Antimicrobial therapy should be continued for at least 7 to 10 days and until fever has resolved, other symptoms have resolved or markedly improved, and blood smears are negative.
More prolonged antimicrobial therapy should be considered for patients with high risk of relapsing babesiosis; these include with B cell lymphoma or other conditions treated with an immunosuppressive regimen (particularly a regimen that includes rituximab or another B cell-depleting agent), patients with malignancy who also are asplenic, patients with solid organ or stem cell transplantation, and patients with HIV/AIDS. For these patients, we administer antimicrobial therapy for at least six consecutive weeks, including two final weeks during which parasites are no longer seen on blood smear.
•Relapse disease — Management of relapsing B. microti infection consists of a repeat course of antibiotic therapy. The antibiotic regimen used for the repeat course can be the same as that used for the initial course (usually azithromycin plus atovaquone).
The duration of antimicrobial therapy is the same as for acute severe illness in patients at high risk of relapsing babesiosis (antimicrobial therapy for at least six consecutive weeks, including two final weeks during which parasites are no longer seen on blood smear).
If relapse occurs despite this approach, the addition of tafenoquine may be considered. (See 'Relapse disease' above.)
●Other babesia species – Regimens for treatment of babesiosis due to B. crassa-like organisms, B. divergens, B. divergens-like organisms, B. duncani, and B. venatorum are discussed above. (See 'Treatment of infection due to other species' above.)
●Coinfection with tick-transmitted pathogens – In the United States, Ixodes scapularis ticks transmit other human pathogens, including Lyme disease and anaplasmosis. Patients with known or suspected babesiosis should be examined carefully for an erythema migrans rash; if present, treatment for Lyme disease is warranted. In addition, for patients treated for babesiosis whose symptoms worsen or do not resolve within the first 48 hours of therapy, we suggest initiating empiric doxycycline therapy, pending laboratory diagnostic data (Grade 2C). (See 'Co-infection with tick-transmitted pathogens' above.)
●Prevention – Prevention of babesiosis consists of personal protective measures that minimize exposure to ticks. (See 'Prevention' above.)
ACKNOWLEDGMENT —
The UpToDate editorial staff acknowledges Jeffrey A Gelfand, MD, FACP, who contributed to earlier versions of this topic review.
