Can Babesiosis Relapse After Treatment?

For most healthy adults, completing a standard frontline treatment—typically a 7-to-10-day course of atovaquone and azithromycin—successfully cures babesiosis ^[1]. However, relapse is a significant risk for specific groups of high-risk patients. When the immune system is severely compromised, it may fail to fully clear the Babesia parasites from the bloodstream, allowing them to multiply again once the medication is stopped ^[2][3].

Understanding who is at risk, why treatments sometimes fail, and what to do if your symptoms return is crucial for a complete recovery.

Who is at Risk for a Relapse?

Relapsing babesiosis primarily affects individuals whose immune systems cannot mount a strong enough defense to eliminate the parasite alongside standard medications. You are considered at much higher risk for a relapse if you fall into one of the following categories ^[4][5][6]:

• Asplenic patients: Individuals who have had their spleen removed (splenectomy) or whose spleen does not function properly. The spleen acts as the body’s primary blood filter, and without it, clearing infected red blood cells is extremely difficult ^[5][7].
• Highly immunocompromised individuals: This includes people undergoing cancer treatments, those living with advanced HIV, or those taking immunosuppressive drugs for autoimmune conditions ^[8][9].
• Patients on B-cell depleting therapies: Medications like rituximab specifically target B-cells, which are vital for creating the antibodies needed to fight off Babesia. Relapses are heavily associated with these therapies ^[10][6].
• The elderly: Age-related weakening of the immune system can also increase the risk of severe, persistent, or relapsing infections ^[11][4].

For these vulnerable groups, standard short-term treatments are often insufficient. The Infectious Diseases Society of America (IDSA) recommends that highly immunocompromised patients receive antimicrobial therapy for at least 6 weeks, continuing until blood smears show no parasites for at least two consecutive weeks ^[9][12].

Why Does Babesiosis Relapse? The Role of Drug Resistance

Sometimes, a relapse occurs not just because the immune system is weak, but because the Babesia microti parasite has mutated to survive the medications. This is known as drug resistance.

During treatment, the parasites can develop specific genetic changes (point mutations) that render frontline therapies ineffective:

• Atovaquone resistance: Mutations in the parasite’s cytochrome b (cytb) gene alter the target site of atovaquone, preventing the drug from working ^[3][13][14].
• Azithromycin and Clindamycin resistance: Mutations in the 23S rRNA gene have been linked to resistance against these standard antibiotics ^[3].

When these mutations occur, you may initially feel better, only to experience a return of symptoms—such as fever, extreme fatigue, and night sweats—after finishing the standard drugs ^[3][6]. While specialized research labs can sequence the parasite’s DNA to find these exact mutations, in everyday practice, doctors usually diagnose treatment failure and suspected resistance based on your returning symptoms and rising parasite counts on routine blood smears and PCR (Polymerase Chain Reaction, a DNA test) tests ^[8].

What to Do If You Suspect a Relapse

If you have finished your babesiosis medication and begin experiencing returning symptoms, do not wait. Contact your infectious disease specialist or primary care doctor immediately. They will need to order a new blood smear and a PCR test to check if the parasite has returned ^[8]. If your symptoms are severe (such as difficulty breathing, severe jaundice, or extreme weakness), seek emergency medical care.

Salvage Therapies: Treating a Relapse

If babesiosis relapses due to a weakened immune system or drug resistance, doctors must turn to “salvage therapies”—alternative treatment plans designed to clear stubborn infections ^[1].

• Tafenoquine: Originally developed as an antimalarial drug, tafenoquine has emerged as a powerful adjunct therapy for treating relapsing, drug-resistant Babesia microti infections ^[2][15]. It is often prescribed alongside atovaquone-proguanil (Malarone) to effectively target the parasite ^[2][16]. Because tafenoquine is prescribed “off-label” for babesiosis, your doctor may need to submit a prior authorization to your insurance company.
• Safety Note on Tafenoquine: Before starting tafenoquine, you must be tested for an enzyme deficiency known as G6PD deficiency. Giving tafenoquine to someone with a G6PD deficiency can trigger a rapid and severe breakdown of red blood cells (hemolytic anemia) ^[17][18].
• Adjusting Immunosuppression: For patients on immune-suppressing drugs, doctors may temporarily lower the dosage or pause the medication (if safely possible) to give your immune system a chance to fight the infection ^[6].
• Emergency Interventions (Exchange Transfusion): In rare, life-threatening cases where the parasite load is dangerously high or your organs begin to fail, doctors may perform an exchange transfusion. This is not a standard relapse treatment, but an emergency procedure that manually removes infected red blood cells and toxins from your body and replaces them with healthy donor blood ^[19][20][21].