Babesia microti Infection Risk in MS Patients on Ocrevus

Tick-borne infection overlooked
Immunosuppression increases risk
Symptoms mimic other conditions
Diagnosis requires suspicion

Babesia microti infection risk may be higher in patients receiving immunosuppressive therapy. A case highlights how coinfections can complicate diagnosis—especially in patients with neurologic disease. :contentReference[oaicite:0]{index=0}

In this Inside Lyme Podcast, I discuss a 54-year-old man with multiple sclerosis (MS) who was ultimately diagnosed with Babesia microti after worsening symptoms and hospitalization.

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Why This Case Matters

Babesia microti is a tick-borne parasite that infects red blood cells and can cause severe illness—particularly in immunocompromised individuals.

A key pattern is vulnerability. Patients on immune-modifying therapies may be at increased risk of infection.

In this case, the patient was receiving ocrelizumab (Ocrevus™), a monoclonal antibody targeting B-cells used to treat multiple sclerosis.

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Immunosuppressive Therapy and Infection Risk

Ocrevus™ is a disease-modifying therapy that alters immune function.

It has been associated with increased risk of infections, including:

• Respiratory infections
• Gastrointestinal infections
• Herpes virus reactivation

A key concern: impaired immune response may allow tick-borne infections to persist or become more severe.

Similar therapies, such as rituximab, have been linked to severe or relapsing Babesia microti infections.

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Clinical Course: Missed Signals

The patient had a long history of multiple sclerosis and worsening symptoms over time.

After starting Ocrevus™, he developed:

• Fever
• Fatigue
• Malaise
• Syncope

He was hospitalized and initially treated for possible sepsis.

A key pattern is misattribution. Symptoms were not immediately linked to tick-borne infection.

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Diagnosis: Babesia Identified

As part of a broader evaluation, PCR testing confirmed Babesia microti.

This highlights an important point: testing for coinfections may be necessary in complex cases.

Learn more about Lyme coinfections.

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Treatment and Outcome

The patient was treated with:

• Azithromycin
• Atovaquone

After 8 weeks of therapy:

• PCR testing was negative
• Blood smear normalized
• Symptoms resolved

A key pattern is reversibility. Appropriate treatment led to recovery.

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Why Babesia Can Be Missed

Babesia infection can be difficult to diagnose because:

• Symptoms overlap with Lyme disease and other conditions
• Patients may already have complex diagnoses (e.g., MS)
• Testing is not always performed initially

A key pattern is overlap. Coinfections can complicate clinical presentation.

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Clinical Takeaway

Babesia microti infection risk should be considered in patients with unexplained symptoms—especially those on immunosuppressive therapy.

Testing for tick-borne coinfections may be critical in complex or treatment-resistant cases.

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Listen to the Episode

Inside Lyme Podcast: Babesia microti in a multiple sclerosis patient

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Key Questions Covered

1. What is Babesia microti?
2. How is Babesia diagnosed?
3. How accurate is testing?
4. Who is at risk for severe infection?
5. How does immunosuppression affect outcomes?

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Reference

1. Haberli N et al. Mult Scler Relat Disord. 2021.

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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