Babesia Coinfection Treatment When Lyme Therapy Fails
Babesia requires different treatment than Lyme disease
Atovaquone plus azithromycin is the best-studied first-line combination
Severe illness requires attention to the whole clinical picture
When Lyme disease treatment fails to resolve symptoms, a coinfection such as Babesia may be part of the explanation. Understanding Babesia treatment options can change the recovery path for patients who remain ill despite Lyme therapy.
Babesia is a protozoan parasite rather than a bacterium. Because it infects red blood cells, the medications used for Lyme disease alone may not adequately treat babesiosis.
A 2025 study of hospitalized patients with babesiosis also provides useful new information about treatment of severe disease. The findings reinforce an important principle: treatment decisions should consider the patient’s overall clinical condition and organ involvement rather than relying on the percentage of infected red blood cells alone.4
Why Babesia Treatment Matters
When patients remain ill after Lyme disease treatment, coinfections such as Babesia are one possible explanation.
Babesia is a protozoan parasite and requires treatment directed against the parasite rather than standard Lyme disease antibiotics alone.
This distinction helps explain why some patients may continue to experience symptoms despite receiving treatment directed at Lyme disease.
Persistent fatigue, sweats, chills, air hunger, headaches, dizziness, or other symptoms are not specific enough to diagnose Babesia by themselves. The diagnosis should be considered in the context of exposure, laboratory findings, clinical presentation, and appropriate testing.
For a broader overview, see Babesia Symptoms and Treatment.
First-Line Babesia Coinfection Treatment
One of the most important clinical trials of babesiosis treatment was published by Krause and colleagues in the New England Journal of Medicine.1
The researchers compared atovaquone plus azithromycin with clindamycin plus quinine in patients with non-life-threatening babesiosis.
Both regimens were effective, but atovaquone plus azithromycin was substantially better tolerated.1
The study used Mepron, an atovaquone liquid suspension, paired with azithromycin.
Atovaquone is available in different formulations used clinically:
- Mepron – liquid atovaquone, the formulation used in the original clinical trial
- Malarone – tablets containing atovaquone plus proguanil, approved for malaria and sometimes used off-label in babesiosis
Malarone was not the formulation evaluated in the original Babesia treatment trial. Its use for babesiosis therefore should not be assumed to have the same clinical evidence as atovaquone plus azithromycin.
Azithromycin can prolong the QT interval in susceptible patients, so cardiac risk and other QT-prolonging medications may need to be considered.
Important: Atovaquone absorption improves when the medication is taken with food, particularly food containing fat.
Is Malarone Used for Babesia?
Yes. Malarone contains atovaquone plus proguanil and is sometimes prescribed off-label for babesiosis.
The tablet formulation may be easier for some patients to take than liquid atovaquone.
However, it is important to distinguish clinical practice from published evidence. The landmark randomized babesiosis trial evaluated atovaquone plus azithromycin, not Malarone.1
The choice of formulation and combination should therefore be individualized based on the clinical situation, medication tolerance, and treatment history.
Dose Considerations for Sensitive Patients
Not every patient tolerates medications in the same way. Gastrointestinal sensitivity, medication interactions, autonomic symptoms, or previous adverse reactions may complicate treatment.
In selected patients, clinicians may adjust dosing based on tolerance and clinical circumstances.
Malarone is available in two commonly used tablet strengths:
- Adult tablets: 250 mg atovaquone / 100 mg proguanil
- Pediatric tablets: 62.5 mg atovaquone / 25 mg proguanil
The smaller formulation can provide additional flexibility when dosing needs to be individualized.
Patients with substantial medication sensitivity still require careful clinical monitoring because lowering or changing a dose can also affect treatment effectiveness.
Babesia Treatment Duration in Complex Cases
Many treatment recommendations for uncomplicated acute babesiosis are based on relatively short courses of therapy.
Current guidelines generally recommend 7–10 days of treatment for immunocompetent patients with uncomplicated babesiosis, while immunocompromised patients with persistent or relapsing infection may require substantially longer treatment.3
Clinical situations can become more complicated when a patient has:
- delayed diagnosis
- severe illness
- persistent or recurrent symptoms
- impaired immunity
- additional tick-borne infections
- difficulty tolerating medication
Treatment duration may therefore depend on the type of babesiosis being treated and the individual patient’s response.
For a more detailed discussion, see Babesia Treatment Duration: Why 7–10 Days May Not Be Enough.
How Is Severe Babesiosis Treated?
Severe babesiosis is different from uncomplicated outpatient infection.
Patients may develop substantial anemia, kidney injury, altered mental status, respiratory failure, abnormal chest imaging, high parasitemia, or other evidence of organ dysfunction.
A 2025 retrospective study by Williams and colleagues examined 147 adults hospitalized with confirmed babesiosis at Westchester Medical Center between 2006 and 2023.4
Sixty-three patients met the study’s criteria for severe babesiosis, 41 required intensive care, and 10 died.4
The majority of the entire cohort—75%—ultimately received azithromycin plus atovaquone. Eight percent received clindamycin plus quinine, while other combinations were used in the remaining patients.4
Importantly, among patients with severe babesiosis, the investigators did not find a statistically significant mortality difference between patients treated with clindamycin plus quinine and those treated with atovaquone plus azithromycin.4
This was an observational study rather than a randomized treatment trial, so it cannot establish that the regimens are equivalent in every form of severe babesiosis. However, it provides useful real-world evidence about how hospitalized babesiosis is currently treated.
Clindamycin and Quinine Are No Longer the Only Option for Severe Disease
Historically, clindamycin plus quinine was commonly used for severe babesiosis.
However, quinine can be difficult to tolerate. Adverse effects can include tinnitus, hearing changes, dizziness, nausea, vomiting, and other symptoms.
Current guidelines favor atovaquone plus azithromycin for most patients, including many hospitalized patients, while clindamycin plus quinine remains an alternative regimen.3
The Westchester investigators observed that treatment practices changed during the long study period. Earlier in the cohort, clinicians were more likely to use clindamycin plus quinine for severe disease. Later practice increasingly favored atovaquone plus azithromycin because of its tolerability and clinical effectiveness.4
Treatment still needs to be individualized when a patient is critically ill, unable to tolerate first-line therapy, or failing to respond adequately.
Does High Parasitemia Determine How Severe Babesiosis Is?
Parasitemia—the percentage of red blood cells containing Babesia parasites—is an important measurement in acute babesiosis.
Higher parasitemia was associated with severe disease in the Westchester study. But parasite percentage did not tell the entire story.4
Most patients in the study had parasitemia below 10%, and severe disease could occur without parasite levels exceeding that threshold.
The investigators concluded that organ dysfunction, severe dyspnea, and abnormal chest imaging were associated with worse outcomes regardless of the parasitemia level.4
This means that parasitemia should be interpreted together with the patient’s overall clinical condition rather than used as the only measure of severity.
When Is Exchange Transfusion Considered?
Red blood cell exchange transfusion has traditionally been considered for selected patients with severe babesiosis, particularly those with high parasitemia or significant organ dysfunction.
In the Westchester study, 31 of 147 patients underwent red blood cell exchange transfusion.4
Among patients with severe disease, the researchers did not find a statistically significant mortality difference between those who received exchange transfusion and those who did not.4
That finding does not establish that exchange transfusion is ineffective. The study was retrospective, and the patients selected for exchange transfusion may have differed substantially from those who did not receive it.
Instead, the study adds to an important clinical question: should the decision to perform exchange transfusion be driven by a fixed parasite percentage, or by the patient’s overall clinical condition?
Current guidelines recommend considering exchange transfusion in selected patients with severe babesiosis, particularly when there is high-grade parasitemia or severe pulmonary, renal, or hepatic compromise.3
The 2025 findings reinforce the importance of considering organ dysfunction and clinical severity alongside parasitemia.4
Alternative Babesia Treatment Approaches
Atovaquone plus azithromycin remains the primary evidence-supported combination for uncomplicated babesiosis.1,3
Other combinations may be considered in selected circumstances when standard therapy cannot be used or when another tick-borne infection also requires treatment.
For example, atovaquone plus doxycycline has not been established as a standard Babesia regimen in randomized treatment trials. A clinician might nevertheless use doxycycline when Anaplasma or Ehrlichia infection also needs to be treated or when another medication cannot be used.
Such combinations should be distinguished from regimens supported by clinical babesiosis treatment trials.
Emerging Options for Refractory Babesia
Tafenoquine is an antimalarial medication that has demonstrated activity against Babesia microti in experimental studies.
A 2022 case report described an immunocompromised patient with relapsing babesiosis and clinical and molecular evidence of resistance to azithromycin and atovaquone. Tafenoquine was used as part of the treatment strategy, and the patient improved.2
That report is encouraging but represents a single patient rather than a clinical trial.
Tafenoquine therefore remains an off-label and emerging option rather than an established first-line treatment for babesiosis.
Important safety consideration: G6PD testing is required before tafenoquine because patients with G6PD deficiency are at risk for hemolytic anemia.
What Improvement May Look Like
Recovery from babesiosis does not look identical in every patient.
Symptoms that may improve as the illness responds to treatment include:
- air hunger
- night sweats
- fever or chills
- fatigue
- sleep disruption
- reduced stamina
- exercise intolerance
- cognitive complaints
In acute severe babesiosis, objective findings such as anemia, thrombocytopenia, parasitemia, kidney dysfunction, or other organ abnormalities may also require monitoring.
Persistent symptoms after treatment should not automatically be assumed to represent ongoing Babesia infection. Treatment response, repeat testing when appropriate, coinfections, post-infectious effects, medication complications, and unrelated conditions may all need consideration.
Clinical Monitoring During Treatment
Monitoring depends on the severity of illness and the medications being used.
Evaluation may include:
- complete blood count to monitor anemia and other blood cell changes
- blood smear or PCR in selected patients with acute or severe babesiosis
- liver function testing
- kidney function testing when clinically indicated
- parasitemia monitoring in severe acute disease
- EKG monitoring in selected patients receiving azithromycin or other QT-prolonging medications
Monitoring becomes particularly important when a patient has severe illness, impaired immunity, substantial anemia, organ dysfunction, or persistent parasitemia.
When Treating Babesia Changes Recovery
Patients who remain ill after Lyme disease treatment may improve when an unrecognized Babesia infection is identified and appropriately treated.
However, persistent symptoms following Lyme treatment have multiple possible explanations. Babesia should be considered when the clinical presentation supports it rather than assumed to be present solely because Lyme treatment did not resolve every symptom.
For more on the interaction between these infections, see Babesia and Lyme Disease: Why Coinfection Makes Recovery Harder.
Clinical Perspective
Babesia coinfection can be one reason a patient remains ill despite treatment directed at Lyme disease because the two infections require different treatment strategies.
The 2025 Westchester study adds an important lesson for patients with severe babesiosis: the parasite percentage is important, but it should not be the only factor used to judge severity.4
Severe dyspnea, abnormal chest imaging, kidney injury, mental status changes, anemia, and other evidence of organ dysfunction may provide important information about how sick a patient is.
Treatment decisions therefore require integration of the infection, the patient, the severity of illness, medication tolerance, laboratory findings, organ involvement, and response to therapy.
Clinical Takeaway
Babesia requires treatment distinct from Lyme disease, which is why an unrecognized coinfection may contribute to persistent illness after Lyme therapy.
Atovaquone plus azithromycin remains the best-supported and generally better-tolerated treatment combination for uncomplicated babesiosis.1,3
A 2025 study of hospitalized babesiosis also found that atovaquone plus azithromycin was commonly used in severe disease and that clinical severity could not be determined by parasitemia alone.4
For severe babesiosis, the patient’s organ function, respiratory status, laboratory abnormalities, parasitemia, and overall clinical condition all matter when treatment decisions are made.
Frequently Asked Questions
What is the most common treatment for Babesia?
Atovaquone combined with azithromycin is the preferred treatment for most patients with babesiosis and was shown in a randomized clinical trial to be effective and substantially better tolerated than clindamycin plus quinine.
Can Malarone be used for Babesia?
Malarone contains atovaquone plus proguanil and is sometimes used off-label for babesiosis. However, the landmark clinical trial evaluated liquid atovaquone combined with azithromycin rather than Malarone.
How is severe babesiosis treated?
Severe babesiosis generally requires hospitalization and close monitoring. Atovaquone plus azithromycin or alternative therapy may be used depending on the clinical situation. Selected patients with high parasitemia or severe organ dysfunction may also be considered for exchange transfusion.
Does parasitemia determine how severe Babesia is?
No. Higher parasitemia can be associated with severe babesiosis, but the percentage of infected red blood cells does not capture the entire clinical picture. Organ dysfunction, respiratory problems, kidney injury, anemia, mental status changes, and other findings also matter.
Does every patient with more than 10% parasitemia need exchange transfusion?
Not necessarily. Parasitemia is one consideration, but current recommendations also consider severe pulmonary, renal, or hepatic compromise. A 2025 retrospective study adds to evidence that clinical status should be considered alongside parasite percentage.
Can Babesia explain why Lyme treatment did not work?
Sometimes. Lyme disease and babesiosis require different treatments, so an unrecognized Babesia infection can contribute to persistent symptoms after Lyme therapy. However, persistent symptoms have many possible causes and do not by themselves establish Babesia infection.
Related Articles
These articles provide additional information about Babesia symptoms, treatment duration, Lyme disease coinfection, and treatment response.
- Babesia Symptoms and Treatment
- Babesia Treatment Duration: Why 7–10 Days May Not Be Enough
- Babesia and Lyme Disease: Why Coinfection Makes Recovery Harder
- Night Sweats Babesia: The Symptom Doctors Miss
- Babesia Treatment: Why Doxycycline Doesn’t Work
References
- Krause PJ, Lepore T, Sikand VK, et al. Atovaquone and azithromycin for the treatment of babesiosis. N Engl J Med. 2000;343(20):1454-1458. doi:10.1056/NEJM200011163432004.
- Marcos LA, Leung A, Kirkman L, Wormser GP. Use of tafenoquine to treat a patient with relapsing babesiosis with clinical and molecular evidence of resistance to azithromycin and atovaquone. IDCases. 2022;27:e01460. doi:10.1016/j.idcr.2022.e01460.
- Krause PJ, Auwaerter PG, Bannuru RR, et al. Clinical Practice Guidelines by the Infectious Diseases Society of America (IDSA): 2020 Guideline on Diagnosis and Management of Babesiosis. Clin Infect Dis. 2021;72(2):e49-e64. doi:10.1093/cid/ciaa1216.
- Williams G, Tatem L, Ghosh K, Pascual AG, Kapinos P, Mordue DG, El Khoury MY. Pulmonary Manifestations of Babesiosis and Predictors of Mortality from a Quaternary Care Center in Westchester, New York. Pathogens. 2025;14(4):376. doi:10.3390/pathogens14040376.
This article is for educational purposes and is not a substitute for individualized medical advice, diagnosis, or treatment.
Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.
Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention
