What Are the Different Species of Babesia?
At a Glance
The most common Babesia species in the US is Babesia microti (Northeast/Midwest), while Babesia duncani is found on the West Coast. Knowing which species you have is critical because standard tests often miss B. duncani, and different species may require alternative treatments.
In this answer
3 sections
Yes, there are different species (types) of Babesia that can infect humans, and which one you might encounter depends heavily on where you live or travel. In the United States, the most common species is Babesia microti, which is primarily found in the Northeast and Upper Midwest [1][2]. On the West Coast, a different species called Babesia duncani is the main culprit [3]. Meanwhile, in Europe, the disease is most often caused by Babesia divergens [4]. The specific type of Babesia you have is important because it can affect both how the infection is diagnosed and how severe the symptoms might be.
Where Different Species Live
Babesia parasites are spread by tick bites. Because different ticks live in different regions and carry different types of parasites, the geographic breakdown looks like this (remember that travel history is just as important as your current residence when considering your risk):
- Northeast and Upper Midwest (US): This area is home to Babesia microti. It is spread by the black-legged tick (Ixodes scapularis), the same tick that carries Lyme disease [5][6].
- West Coast and Pacific Northwest (US/Canada): Babesia duncani is found here, though recent research shows its geographic footprint may be wider across North America than previously recognized [3][7].
- Europe: Babesia divergens is the most common cause of human babesiosis in Europe [4][8].
- Other US Variants: An emerging species called Babesia odocoilei has recently been identified in the US [9]. Additionally, very rare cases of a species called B. divergens-like (or MO-1) have been found in the US, typically in individuals who do not have a spleen [10][11].
How the Species Affects Testing
Knowing where you live or where you have traveled is critical for your doctor because standard blood tests do not catch all species of Babesia.
Many common diagnostic panels are designed specifically to look for Babesia microti [7]. If you have a B. duncani infection, standard B. microti tests may come back negative, even if you are actively sick [7]. To accurately diagnose species other than B. microti, specialized tests must be ordered by your doctor [7][12]. These might include:
- Specific antibody tests, such as an Immunofluorescence Assay (IFA)
- Targeted DNA tests, like a Polymerase Chain Reaction (PCR) or Fluorescence In Situ Hybridization (FISH)
- Antigen capture tests.
(Note: For newly emerging species like B. odocoilei, standard specialized tests might sometimes miss the infection, occasionally requiring advanced reference labs for detection.)
Differences in Severity and Treatment
The species of Babesia can influence how sick you feel and how your infection is treated:
- Symptom Severity: Babesia divergens in Europe is generally recognized as causing the most severe form of human babesiosis [4]. In the US, B. microti can also cause severe complications that require hospitalization, particularly in older adults or immunocompromised individuals [13][14].
- Treatment Resistance: The standard treatment for B. microti usually involves a combination of two drugs: atovaquone and azithromycin. However, research indicates that Babesia duncani has a low susceptibility to this standard regimen [15][16]. This means that if you have B. duncani, those medications might not work as effectively. Fortunately, there are well-established backup options—your doctor may prescribe an alternative combination, such as clindamycin and quinine or newer antiparasitic protocols, to successfully treat the infection [15].
- Coinfections: If you are bitten by a tick carrying multiple diseases, being co-infected with Babesia and other pathogens (like Lyme disease or anaplasmosis) can significantly increase the severity and duration of your illness [17]. However, doctors can test for and treat these coinfections simultaneously, helping to ensure a comprehensive recovery.
Common questions in this guide
What is the difference between Babesia microti and Babesia duncani?
Will standard tick-borne disease tests detect Babesia duncani?
How does the treatment differ based on the species of Babesia?
Do coinfections like Lyme disease affect babesiosis?
Questions to Ask Your Doctor
Curated prompts to bring to your next appointment.
- 1.Given my recent travel history, could my negative test be due to a different species like Babesia duncani?
- 2.Are the tick-borne disease panels we are using broad enough to detect species other than Babesia microti, or should we use species-specific IFA or FISH tests?
- 3.If my symptoms point to a Babesia duncani infection, what is your experience using alternative treatment protocols if the standard medications are ineffective?
- 4.Should we also test for common tick-borne coinfections, such as Lyme disease or anaplasmosis, at the same time?
- 5.How do my underlying health conditions (like a missing spleen or weakened immune system) affect which tests and treatments we should pursue?
Questions For You
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References
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This page provides educational information about different Babesia species and is not a substitute for professional medical advice. Always consult an infectious disease specialist or your healthcare provider regarding accurate tick-borne disease testing and treatment.
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