Can Babesiosis Look Like Sepsis?

Babesiosis can resemble a severe systemic infection
Fever, low platelets, and hemolysis can provide important clues
Severe cases can progress to sepsis and organ dysfunction

Can babesiosis look like sepsis? Yes. Babesiosis can initially resemble sepsis because both can present with fever, chills, weakness, abnormal laboratory findings, and evidence of organ dysfunction. Severe babesiosis can also progress to a clinical syndrome diagnosed as sepsis.^1,2

A 2025 case illustrates how easily the diagnosis can be missed. A 52-year-old woman with recent tick exposure presented with fever, chills, body aches, malaise, and poor oral intake. She was initially treated for suspected sepsis before a blood smear revealed organisms consistent with Babesia and parasitemia greater than 5%.¹

A larger 2026 multicenter study provides additional evidence that sepsis is an important complication of babesiosis. Among 1,566 adults with PCR-confirmed babesiosis, 159, or 10.2%, were identified as having sepsis. Those patients had higher rates of acute kidney injury, shock, hemolytic anemia, and mortality.²

The findings reinforce an important clinical point: after a tick bite, a severe febrile illness should not automatically be assumed to be Lyme disease or routine bacterial sepsis.

Why Can Babesiosis Resemble Sepsis?

Babesia is a parasite that infects red blood cells. Symptomatic infection can cause fever, chills, sweats, fatigue, headache, and body aches. More severe disease can produce hemolytic anemia, thrombocytopenia, kidney or liver dysfunction, respiratory complications, shock, and other manifestations of systemic illness.³

Many of these findings overlap with illnesses that commonly lead clinicians to consider sepsis. The diagnosis may be particularly difficult when the patient does not initially know that a tick bite occurred or when attention is focused on more familiar causes of fever.

For a broader discussion of the range of symptoms associated with this infection, see Babesia symptoms and treatment.

What Laboratory Findings May Point Toward Babesiosis?

Routine laboratory testing can provide useful clues. IDSA notes that characteristic abnormalities in babesiosis can include anemia, thrombocytopenia, elevated liver enzymes, and evidence of intravascular hemolysis, including elevated lactate dehydrogenase, increased bilirubin, and reduced haptoglobin.³

The patient described by Haymov and colleagues had several of these abnormalities. Her platelet count was 37,000/µL on admission and fell to 20,000/µL. Her hemoglobin declined from 11.0 to 8.7 g/dL, haptoglobin was below 10 mg/dL, lactate dehydrogenase was elevated, and AST and ALT were elevated.¹

These findings are not specific to babesiosis. However, the combination of fever, tick exposure, thrombocytopenia, anemia, and evidence of hemolysis should raise consideration of babesiosis in the appropriate geographic and clinical setting.

A Negative Lyme Test Does Not Exclude Another Tick-Borne Infection

Another useful feature of the 2025 case was that the patient’s Lyme IgM and IgG tests were negative.¹

That result did not answer the broader question of whether she had a tick-borne infection. The same blacklegged ticks associated with Lyme disease can transmit Babesia microti, and the diagnostic tests used for Lyme disease do not diagnose babesiosis.

This is one reason clinicians may need to consider more than one tick-borne illness when symptoms and laboratory abnormalities do not fit Lyme disease alone. A broader overview is available in the Lyme disease coinfections guide.

How Is Acute Babesiosis Confirmed?

Current IDSA guidelines recommend confirming acute babesiosis with a peripheral blood smear or polymerase chain reaction (PCR), rather than relying on antibody testing alone.³

A blood smear may directly demonstrate parasites inside red blood cells. The classic Maltese cross configuration is highly characteristic, although it is not always seen. PCR can be particularly useful when parasite levels are too low to be readily detected on a smear.³

In the Haymov case, a smear initially performed while evaluating for malaria revealed intracellular organisms resembling Babesia, with parasitemia reported above 5%. The diagnosis was subsequently confirmed by pathology.¹

Testing still needs to be interpreted in the clinical context. Exposure history, symptoms, blood counts, evidence of hemolysis, immune status, and illness severity all contribute to determining how strongly babesiosis should be considered.

Babesiosis Can Resemble Sepsis — and Can Also Cause Sepsis

There is an important distinction between a patient whose presentation looks like sepsis and a patient who develops babesiosis-related sepsis.

The 2025 case primarily illustrates the first problem: the patient initially appeared to have a systemic illness concerning enough for clinicians to begin cefepime and vancomycin for suspected sepsis before babesiosis was recognized.¹

The 2026 study by Long and colleagues addressed the second issue more directly. Researchers used a large multicenter database to identify adults with PCR-confirmed babesiosis between 2010 and 2024. Of 1,566 patients, 159 were identified as having sepsis based on diagnostic codes.²

Older age and several cardiac or renal comorbidities were associated with babesiosis-related sepsis. Patients classified as having sepsis also experienced more acute kidney injury, shock, and hemolytic anemia and had higher mortality at 30 days, 90 days, and one year.²

Because this was a retrospective database study using diagnostic codes to define sepsis, it cannot determine precisely why individual patients became critically ill or establish that the identified risk factors caused sepsis. Nevertheless, the findings show that sepsis is an important recognized presentation and complication of babesiosis.

Who Is at Greater Risk for Severe Babesiosis?

Babesiosis ranges from asymptomatic infection to life-threatening illness. Older adults, people without a functioning spleen, and immunocompromised patients are among those at increased risk for severe disease.³

The 2026 study adds to this picture by finding associations between babesiosis-related sepsis and older age as well as predominantly cardiac and renal comorbidities.²

Risk factors can help clinicians judge severity, but they should not be used to assume that an otherwise healthy patient cannot become seriously ill. The clinical presentation and laboratory findings still matter.

Frequently Asked Questions

Can babesiosis look like bacterial sepsis?

Yes. Babesiosis can cause fever, chills, weakness, thrombocytopenia, hemolytic anemia, elevated liver enzymes, kidney dysfunction, and other abnormalities that can resemble severe bacterial infection. Some patients with babesiosis also develop sepsis.

What blood test findings suggest babesiosis?

Babesiosis may be associated with anemia, low platelets, elevated liver enzymes, increased lactate dehydrogenase or bilirubin, and reduced haptoglobin from hemolysis. These abnormalities are not specific to Babesia and must be interpreted with the clinical history.

Can you have babesiosis with a negative Lyme test?

Yes. Lyme disease and babesiosis are different infections and require different diagnostic tests. A negative Lyme disease test does not exclude Babesia infection.

How is acute babesiosis confirmed?

Acute babesiosis is generally confirmed by identifying Babesia on a peripheral blood smear or detecting Babesia DNA with PCR. Antibody testing alone cannot reliably distinguish active from past infection.

Can babesiosis become life-threatening?

Yes. Severe babesiosis can be associated with hemolytic anemia, kidney or liver dysfunction, respiratory complications, shock, sepsis, and other serious complications, particularly in higher-risk patients.

Clinical Takeaway

Babesiosis can initially resemble sepsis because fever, systemic illness, low platelets, anemia, abnormal liver tests, and organ dysfunction can occur with both conditions. Severe babesiosis can also progress to a syndrome diagnosed as sepsis.

The combination of tick exposure, thrombocytopenia, anemia, and evidence of hemolysis should raise consideration of babesiosis, even when Lyme disease testing is negative. Blood smear and PCR are the principal methods used to confirm acute infection.

When a patient becomes seriously ill after tick exposure, the diagnostic question should extend beyond Lyme disease alone.

Related Articles

Babesiosis can present in several different ways, and these articles explore adjacent clinical patterns and complications.

Babesia Symptoms Can Vary: 5 Cases That Show Why It’s Missed
Can Babesia Cause Long-Term Fatigue and Neurological Symptoms?
Babesia Air Hunger: Why Breathing Feels Manual

References

1. Haymov A, Baloch S, Girardin CR. Diagnosing and Managing Babesiosis: A Case Study of Timely Intervention in a Tick-Borne Illness. Cureus. 2025;17(2):e79658.
2. Long J, Henao-Martínez AF, Rau N, Vorkas CK, Marcos LA. Babesiosis-Related Sepsis: Clinical Characteristics and Outcomes from a Multicenter Retrospective Global Research Network Analysis. Am J Trop Med Hyg. 2026;114(4):711-715.
3. Krause PJ, Auwaerter PG, Bannuru RR, et al. Clinical Practice Guidelines by the Infectious Diseases Society of America: 2020 Guideline on Diagnosis and Management of Babesiosis. Clin Infect Dis. 2021;72(2):e49-e64.

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