Babesia duncani emerges in Eastern U.S. and may go undetected

The tick-borne illness Babesia duncani (B. duncani) was initially identified in the western regions of the United States. The disease has always been presumed to be confined to the West Coast, while its counterpart – Babesia microti (B. microti) has been well established on the East Coast.


New research indicates, however, there may no longer be a division of babesial strains between the East Coast and the West Coast. In their article “Babesia microtiBorrelia burgdorferi Co-infection,” Parveen reports that B. duncani has now been identified in eastern USA and Canada.¹

“Since B. duncani is widespread in Canada, its southern spread into northeastern U.S., an area already endemic for Lyme disease, makes co-infections with B. duncani and B. burgdorferi [Lyme disease] a possibility that needs to be carefully investigated.”

“While this review focuses on co-infection with B. microti and B. burgdorferi, there is some evidence that co-infections with a different Babesia species, B. duncani, and B. burgdorferi may be more common than previously suspected,” writes Parveen.

Babesia duncani emerges as a threat on the East Coast and in Canada. Click To Tweet

The authors raise concerns regarding treatment given that, “Antibiotics used against B. microti are less effective against B. duncani, making treatment of B. duncani potentially more challenging.”

“Clinical cases caused by Babesia duncani have been associated with high parasite burden, severe pathology, and death,” writes Abraham in The Journal of Biological Chemistry²

Animals fared worse. “In both mice and hamsters, the parasite causes uncontrolled fulminant infections, which ultimately lead to death,” writes Abraham.

Treatment for B. microti was not as effective for B. duncani in vitro culture, explains Abraham.

“Using this in vitro culture assay, we found that B. duncani has low susceptibility to the four drugs recommended for treatment of human babesiosis, atovaquone, azithromycin, clindamycin, and quinine.”

“These data suggest that current practices are of limited effect in treating the disease [B. duncani],” writes Abraham.

Editor’s note: I have diagnostic concerns. B. duncani is not routinely tested for in Canada and the Eastern USA. Individuals with B. duncani may go undiagnosed.


  1. Parveen N, Bhanot P. Babesia microti-Borrelia Burgdorferi Coinfection. Pathogens. 2019 Jul 31;8(3). pii: E117. doi: 10.3390/pathogens8030117. Review.
  2. Abraham A, Brasov I, Thekkiniath J, Kilian N, Lawres L, Gao R, DeBus K, He L, Yu X, Zhu G, Graham MM, Liu X, Molestina R, Ben Mamoun C. Establishment of a continuous in vitro culture of Babesia duncani in human erythrocytes reveals unusually high tolerance to recommended therapies. J Biol Chem. 2018 Dec 28;293(52):19974-19981.
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12 Replies to "Babesia duncani emerges in Eastern U.S. and may go undetected"

  • Shari Damaso
    01/02/2021 (10:45 am)

    So what is an effective treatment for Babesia Duncani?

    • Dr. Daniel Cameron
      01/03/2021 (7:58 am)

      I start my patients with the same medications I use for Babesia microti e.g. azithromycin and atovaquone. I hope this research into Babesia duncani offers new insights.

  • Joel P.
    01/23/2020 (4:12 pm)

    I have been diagnosed with B. Duncani twice. I live in NYC, travel north on the summer only. I believe I’ve had it with me for many years & is only showing it’s ugly face now. Seem to be responding to Malarone & Mepron, but symptoms come back within 36 hours of stopping the medication. Doing this for 3 months.

    • Dr. Daniel Cameron
      01/23/2020 (8:17 pm)

      I have a similar experience in some patients in my practice.

      • Joel P.
        03/05/2020 (3:27 pm)

        How are you treating Duncani if Malarone & Mepron dont seem to kick it?

        • Dr. Daniel Cameron
          03/05/2020 (7:59 pm)

          I have had the same issues with Babesia microti. Sometimes I need to make sure other tick-borne infections are being treated. I have to make sure there is no other illness. I have tried clindamycin and quinine in a few cases. I have always had an interest in Flagyl or Tindamax as they work for parasites.

          • Henry
            03/28/2020 (7:52 pm)

            I tested positive for Babesia Duncani and I believe I contracted it in Northern VA. My doctor have me do 30 days of Mepron and Azithromycin. I then did 3 days of heavy Tinidazole/Tindamax. Im now starting my 2nd round of Mepron and Azithromycin. Has anyone had success with this regiment?

        • Angela
          01/11/2021 (5:33 pm)

          I’m wondering the same thing.
          My daughter is 12 and has tested positive for b.duncani. She was born in Fl and we have lived in NC since she was 5 months old. We have never been to the west coast so it’s definitely in the east. I’m looking for a good LLD here. She has also tested positive for borrellia miyamotoi.

    • Eric
      09/20/2020 (8:41 am)

      How are you doing now Joel? I start treatment tomorrow for same thing

  • Lynn
    11/09/2019 (1:29 am)

    I was once tested for Babesia duncani at a California Dept of Public Health Lab. Everyone was shocked it came back positive given I’d been infected on the East Coast. The lab director who seemed quite competent swore up and down that this test is accurate and that duncani is a very different species than microti (true). He said there couldn’t possibly be cross reactivity between the two organisms. I did find him believable. The test was repeated and came back positive again. This was back around 2001, so arguably I must have been one of the early victims of this parasite. But if you are looking for a test for this, you might look to the California Dept of Public Health Lab.

  • Beth
    10/23/2019 (3:07 am)

    Is the test for b. ducani reliable?

    • Dr. Daniel Cameron
      10/23/2019 (1:25 pm)

      I have my concerns. I have not seen reliability data in actual practice.

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