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PubMed This is a summary of 21 peer-reviewed journal articles Updated
Infectious Disease

Validation and Orientation: Understanding Babesiosis

At a Glance

Babesiosis is a highly treatable tick-borne infection caused by microscopic parasites that target and destroy red blood cells. Unlike Lyme disease, which is bacterial, Babesiosis is parasitic and requires specific anti-parasitic medications for a full recovery.

Being diagnosed with a tick-borne illness can feel overwhelming, especially when the name is unfamiliar. While many people have heard of Lyme disease, Babesiosis (bah-BEE-zee-oh-sis) is a different type of infection caused by a microscopic parasite rather than bacteria [1]. Understanding how this parasite works and why it is manageable can help you move forward with confidence.

What is Babesiosis?

Babesiosis is an infection caused by complex, single-celled parasites [2]. Unlike Lyme disease, which is bacterial, Babesiosis is more closely related to malaria [1]. These parasites are intraerythrocytic, meaning they specifically target and live inside your erythrocytes (red blood cells) [1][3].

Inside the red blood cell, the parasite reproduces and eventually causes the cell to rupture [4]. One unique feature of Babesiosis is that it does not have a “liver stage” [1]. In diseases like malaria, the parasite hides in the liver before entering the blood; in Babesiosis, the parasite begins its work in the bloodstream immediately after infection [1][5].

The Three Main Species

While there are many types of Babesia, three species are most commonly responsible for human illness:

  • Babesia microti: The most common cause of the disease in the United States, particularly in the Northeast and Upper Midwest [6][7].
  • Babesia duncani: Found primarily on the West Coast of North America, this species can sometimes be more resistant to standard treatments than B. microti [8][9].
  • Babesia divergens: More common in Europe, this species is often associated with more severe illness, particularly in people who have had their spleen removed [10].

How It Spreads

Most people contract Babesiosis through the bite of infected ticks [1]. The specific tick responsible depends on where you live:

  • East Coast & Midwest US: The Ixodes scapularis tick (also known as the black-legged tick or deer tick) [11].
  • West Coast US: The Ixodes pacificus tick [8].
  • Europe: The Ixodes ricinus tick [12].

Because these ticks are often as small as a poppy seed, many patients do not remember being bitten.

While tick bites are the primary cause, the parasite can also be transmitted in other ways:

  • Blood Transfusions: The parasite can survive in donated blood, making transfusion-transmitted babesiosis (TTB) a known risk that blood banks now screen for in many areas [13][14]. Note: Because of this risk, individuals who have been diagnosed with Babesiosis are often permanently restricted from donating blood.
  • Maternal-Fetal Transmission: In rare cases, a pregnant person can pass the infection to their baby before or during birth (congenital transmission) [3][15].

Reassurance for the Newly Diagnosed

It is natural to feel anxious after a diagnosis, but there are several reasons for optimism:

  • Standardized Treatment: Doctors have highly effective, established protocols for treating Babesiosis [16]. (See Standard of Care Treatment).
  • High Success Rates: For most healthy individuals, a standard course of anti-parasitic medication results in a full recovery [16][17].
  • Advanced Diagnostics: Modern testing, such as PCR (which looks for the parasite’s DNA) and high-resolution blood smears, allows doctors to identify the infection accurately [18][19].
  • Clear Monitoring: Because the parasite lives in the red blood cells, doctors can often track your recovery by monitoring your blood counts and looking at samples under a microscope [18].

If you have a weakened immune system or have had your spleen removed, your care team may use a longer treatment course or different medications to ensure the infection is completely cleared [20][21].

Common questions in this guide

What is the difference between Babesiosis and Lyme disease?
While both are transmitted by ticks, Lyme disease is caused by bacteria, whereas Babesiosis is caused by a microscopic parasite. Because of this difference, they require completely different types of medications for treatment.
How do you catch Babesiosis?
Most people get Babesiosis from the bite of an infected tick, often a deer tick or black-legged tick. It can also be transmitted through contaminated blood transfusions or, very rarely, passed from a pregnant mother to her baby.
What are the common symptoms of a Babesia infection?
Because the parasite attacks your red blood cells and can cause anemia, common warning signs include unusual fatigue, dark urine, and jaundice, which is a yellowing of the skin. If you notice these signs, especially after tick exposure, contact your healthcare provider.
Is Babesiosis curable?
Yes. For most healthy individuals, doctors use standardized, highly effective anti-parasitic medications that lead to a full recovery. Your care team will monitor your blood counts to ensure the parasite is completely cleared from your system.
Why is having my spleen removed a risk factor for Babesiosis?
The spleen is a critical organ for filtering damaged red blood cells and fighting off infections in the bloodstream. Individuals who have had their spleen removed or who have a weakened immune system face a higher risk of severe illness and often require a longer course of treatment.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Which specific species of Babesia (such as B. microti or B. duncani) was found in my tests?
  2. 2.Since this was transmitted by a tick, should I also be screened for co-infections like Lyme disease or Anaplasmosis?
  3. 3.Does my medical history, specifically the health of my immune system or my spleen, change how we approach my treatment?
  4. 4.What signs of anemia should I watch for as the parasite interacts with my red blood cells?
  5. 5.How will we monitor my progress to ensure the infection is fully cleared?

Questions For You

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References

References (21)
  1. 1

    Superior real-time polymerase chain reaction detection of Babesia microti parasites in whole blood utilizing high-copy BMN antigens as amplification targets.

    Grabias B, Clement J, Krause PJ, et al.

    Transfusion 2018; (58(8)):1924-1932 doi:10.1111/trf.14642.

    PMID: 29664114
  2. 2

    Vesicular mechanisms of drug resistance in apicomplexan parasites.

    Haldar K, Bhattacharjee S

    Microbiology and molecular biology reviews : MMBR 2025; (89(1)):e0001024 doi:10.1128/mmbr.00010-24.

    PMID: 39853128
  3. 3

    Transfusion-transmitted and community-acquired babesiosis in New York, 2004 to 2015.

    Linden JV, Prusinski MA, Crowder LA, et al.

    Transfusion 2018; (58(3)):660-668 doi:10.1111/trf.14476.

    PMID: 29383735
  4. 4

    Babesia divergens host cell egress is mediated by essential and druggable kinases and proteases.

    Elsworth B, Keroack CD, Rezvani Y, et al.

    Nature microbiology 2026; (11(2)):492-506 doi:10.1038/s41564-025-02238-7.

    PMID: 41593365
  5. 5

    [Clinical characteristics, diagnosis and treatment of human babesiosis: a review].

    Wang F, Jiang JF, Tian J, Du CH

    Zhongguo xue xi chong bing fang zhi za zhi = Chinese journal of schistosomiasis control 2020; (33(2)):218-224 doi:10.16250/j.32.1374.2020168.

    PMID: 34008373
  6. 6

    Prevalence of Babesia in Canadian blood donors: June-October 2018.

    Tonnetti L, O'Brien SF, Grégoire Y, et al.

    Transfusion 2019; (59(10)):3171-3176 doi:10.1111/trf.15470.

    PMID: 31385317
  7. 7

    Spreading of Human Babesiosis in China: Current Epidemiological Status and Future Challenges.

    Chen M, Liu Q, Xue J, et al.

    China CDC weekly 2020; (2(33)):634-637 doi:10.46234/ccdcw2020.176.

    PMID: 34594726
  8. 8

    First record of locally acquired human babesiosis in Canada caused by Babesia duncani: a case report.

    Scott JD

    SAGE open medical case reports 2017; (5()):2050313X17725645 doi:10.1177/2050313X17725645.

    PMID: 28890784
  9. 9

    Establishment of a continuous in vitro culture of Babesia duncani in human erythrocytes reveals unusually high tolerance to recommended therapies.

    Abraham A, Brasov I, Thekkiniath J, et al.

    The Journal of biological chemistry 2018; (293(52)):19974-19981 doi:10.1074/jbc.AC118.005771.

    PMID: 30463941
  10. 10

    Establishment of a stable transfection and gene targeting system in Babesia divergens.

    Cubillos EFG, Snebergerova P, Borsodi S, et al.

    Frontiers in cellular and infection microbiology 2023; (13()):1278041 doi:10.3389/fcimb.2023.1278041.

    PMID: 38156314
  11. 11

    Deployment of a Reservoir-Targeted Vaccine Against Borrelia burgdorferi Reduces the Prevalence of Babesia microti Coinfection in Ixodes scapularis Ticks.

    Vannier E, Richer LM, Dinh DM, et al.

    The Journal of infectious diseases 2023; (227(10)):1127-1131 doi:10.1093/infdis/jiac462.

    PMID: 36416014
  12. 12

    Autochthonous Human Babesiosis Caused by Babesia venatorum, the Netherlands.

    Spoorenberg N, Köhler CF, Vermeulen E, et al.

    Emerging infectious diseases 2024; (30(9)):1934-1938 doi:10.3201/eid3009.240556.

    PMID: 39174031
  13. 13

    Transfusion related babesiosis in a non-endemic region (Western New York).

    Aladeen J, Wadhawan P, Pendyala R, et al.

    Oxford medical case reports 2024; (2024(11)):omae133 doi:10.1093/omcr/omae133.

    PMID: 39575087
  14. 14

    Transfusion-Transmitted Babesiosis.

    Villatoro T, Karp JK

    Archives of pathology & laboratory medicine 2019; (143(1)):130-134 doi:10.5858/arpa.2017-0250-RS.

    PMID: 30376376
  15. 15

    Congenital Babesiosis After Maternal Infection With Borrelia burgdorferi and Babesia microti.

    Saetre K, Godhwani N, Maria M, et al.

    Journal of the Pediatric Infectious Diseases Society 2018; (7(1)):e1-e5 doi:10.1093/jpids/pix074.

    PMID: 28992325
  16. 16

    A Five-Week-Old Twin With Profound Anemia: A Case Report of Asymmetric Congenital Babesiosis.

    Walker S, Coray E, Ginsberg-Peltz J, Smith L

    Cureus 2022; (14(3)):e22774 doi:10.7759/cureus.22774.

    PMID: 35382190
  17. 17

    Management strategies for human babesiosis.

    Smith RP, Hunfeld KP, Krause PJ

    Expert review of anti-infective therapy 2020; (18(7)):625-636 doi:10.1080/14787210.2020.1752193.

    PMID: 32268823
  18. 18

    Case Report: Diagnosis of Hemolytic Anemia from Babesia and Secondary Multi-Pathogen Pneumonia Using a Metagenomic Next-Generation Sequencing Approach.

    Lu Y, Zhang D, Han D, et al.

    Infection and drug resistance 2024; (17()):3785-3791 doi:10.2147/IDR.S472861.

    PMID: 39247756
  19. 19

    A Fluorescence in Situ Hybridization (FISH) Test for Diagnosing Babesiosis.

    Shah JS, Mark O, Caoili E, et al.

    Diagnostics (Basel, Switzerland) 2020; (10(6)) doi:10.3390/diagnostics10060377.

    PMID: 32517217
  20. 20

    Broad Antimicrobial Resistance in a Case of Relapsing Babesiosis Successfully Treated With Tafenoquine.

    Rogers R, Krause PJ, Norris AM, et al.

    Clinical infectious diseases : an official publication of the Infectious Diseases Society of America 2023; (76(4)):741-744 doi:10.1093/cid/ciac473.

    PMID: 35684960
  21. 21

    Clinical and Molecular Evidence of Atovaquone and Azithromycin Resistance in Relapsed Babesia microti Infection Associated With Rituximab and Chronic Lymphocytic Leukemia.

    Simon MS, Westblade LF, Dziedziech A, et al.

    Clinical infectious diseases : an official publication of the Infectious Diseases Society of America 2017; (65(7)):1222-1225 doi:10.1093/cid/cix477.

    PMID: 28541469

This page provides educational information about Babesiosis and its causes. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your infectious disease specialist or primary care doctor for specific health concerns.

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