Babesia duncani: Symptoms, Treatment, and East Coast Spread
Babesia duncani may occur beyond the West Coast
Symptoms can resemble other forms of babesiosis
Testing and treatment remain challenging
Babesia duncani is a tick-borne parasite that infects red blood cells and can cause babesiosis. Although it was initially associated primarily with the western United States, reports and surveillance findings have raised questions about whether its geographic distribution may extend beyond the West Coast.
Symptoms of Babesia duncani can overlap with those caused by Babesia microti. Laboratory studies also suggest that B. duncani may respond differently to commonly used babesiosis medications, making accurate identification and treatment important.
Babesiosis should be considered in patients with compatible symptoms who have been evaluated for Lyme disease and other tick-borne coinfections, particularly when symptoms include unexplained sweats, chills, fatigue, anemia, or shortness of breath.
What is Babesia duncani?
Babesia duncani, formerly called WA1, is an intraerythrocytic parasite, meaning it lives and reproduces inside red blood cells. It is genetically distinct from Babesia microti, the species responsible for most reported babesiosis cases in the northeastern United States.
Babesia parasites are typically transmitted through the bite of an infected tick. Transmission through donated blood is also possible. A review of transfusion-transmitted babesiosis noted that B. duncani has been transmitted through blood transfusion, although only a small number of cases had been reported.7
Researchers can continuously grow B. duncani in human red blood cells in the laboratory. This has allowed investigators to study its genome, virulence, drug susceptibility, and potential treatment targets.3,4
Babesia duncani symptoms
Babesia duncani infection may range from mild or unnoticed illness to severe disease. Symptoms can develop gradually and may resemble influenza or other tick-borne infections.
Reported symptoms of babesiosis, including infections attributed to B. duncani, may include:
- Fever or chills
- Night sweats or daytime sweats
- Profound fatigue
- Headache
- Muscle or body aches
- Shortness of breath, sometimes described by patients as air hunger
- Dizziness
- Poor appetite or nausea
- Hemolytic anemia
- Low platelet counts
Severe babesiosis can involve marked anemia, respiratory distress, organ dysfunction, or death. The risk is generally greater in older adults, people without a functioning spleen, and individuals who are immunocompromised. Nevertheless, the first recognized WA1 infection occurred in a patient without the usual risk factors for severe babesiosis.3,4,6
Is Babesia duncani found on the East Coast?
Historically, B. microti was associated with the Northeast and upper Midwest, while B. duncani was viewed primarily as a West Coast parasite. Newer reports have challenged such a strict geographic division.
In their review of Babesia microti and Borrelia burgdorferi coinfection, Parveen and Bhanot noted evidence suggesting that B. duncani infections may occur more widely than previously suspected, including reports involving Canada and the eastern United States.1
A Canadian surveillance study reported patients with positive B. duncani testing across multiple provinces, with the largest numbers in British Columbia, Ontario, and Québec.5 However, the study relied on aggregate reports from a limited number of clinicians and did not independently verify every case through national public health surveillance.
A subsequent review noted that most molecularly confirmed human cases reported in the United States had occurred in western states and called for additional molecular evidence to clarify the parasite’s geographic range.6
The available evidence suggests that B. duncani may occur beyond the West Coast, but its prevalence in the eastern United States and Canada remains uncertain.
How is Babesia duncani different from Babesia microti?
B. duncani and B. microti both infect red blood cells and can produce similar symptoms, but they are genetically and biologically distinct parasites.
| Feature | Babesia microti | Babesia duncani |
|---|---|---|
| Traditional geographic association | Northeastern and upper midwestern United States | Western United States |
| Current geographic understanding | Well established in multiple endemic states | Reports suggest a broader range, but the distribution remains uncertain |
| Human evidence | Substantial clinical and surveillance data | Fewer confirmed cases and less population-level data |
| Drug susceptibility | Standard treatment regimens are better studied | Laboratory studies suggest lower susceptibility to several commonly used medications |
How is Babesia duncani diagnosed?
Diagnosing B. duncani can be difficult because routine Babesia testing may focus primarily on B. microti. A negative B. microti test does not necessarily exclude infection with another Babesia species.
Diagnostic methods may include:
- Microscopic examination of a peripheral blood smear
- Polymerase chain reaction testing for Babesia DNA
- Species-specific antibody testing
- Blood counts and markers of hemolysis
Babesia species can look similar under the microscope. Molecular testing or DNA sequencing may therefore be needed to identify the species reliably.6
Testing may also be negative when the number of circulating parasites is low. Diagnosis may require consideration of symptoms, exposure history, immune status, laboratory abnormalities, and the limitations of available assays. For some patients, Babesia remains a clinical diagnosis despite inconclusive testing.
Babesia duncani treatment
There is no widely established treatment regimen based on controlled human trials specifically involving B. duncani. Treatment has generally been adapted from regimens used for other forms of babesiosis.
Treatment approaches used for human babesiosis include:
- Atovaquone with azithromycin
- Clindamycin with quinine in selected severe cases
Individualized regimens may be considered in selected persistent, severe, or relapsing cases based on immune status, treatment tolerance, laboratory findings, and clinical response.
Abraham and colleagues established a continuous laboratory culture of B. duncani and found low in vitro susceptibility to atovaquone, azithromycin, clindamycin, and quinine.2
These findings raise concern that medications commonly used for B. microti may have reduced activity against B. duncani. However, an in vitro study cannot establish how consistently a medication will succeed or fail in patients.
New Babesia duncani treatment research
A 2022 study identified two investigational endochin-like quinolone prodrugs, ELQ-331 and ELQ-468, that showed activity against B. duncani and B. microti in laboratory and mouse models.4
A 2023 multi-omics study mapped the B. duncani genome and identified possible virulence factors, diagnostic antigens, metabolic pathways, and drug targets. Laboratory testing identified the antifolates pyrimethamine and WR-99210 as potent inhibitors of parasite development in red blood cells.3
Tafenoquine has also shown activity against B. duncani in laboratory and mouse studies. In experimental models, tafenoquine combined with atovaquone prevented recrudescence.8
Human tafenoquine evidence has primarily involved highly immunocompromised patients with relapsing B. microti infection, not confirmed human B. duncani infection.9 Tafenoquine is therefore not an established treatment for human B. duncani.
Tafenoquine requires quantitative glucose-6-phosphate dehydrogenase testing before use because it can cause clinically significant hemolysis in patients with G6PD deficiency. More information is available in my discussion of tafenoquine for relapsing Babesia.
Babesia duncani and Lyme disease coinfection
Patients can be exposed to both Babesia and Borrelia burgdorferi. A patient with Lyme disease who also has babesiosis may experience sweats, chills, air hunger, anemia, or persistent fatigue that is not fully explained by Lyme disease alone.
Parveen and Bhanot focused primarily on B. microti and Lyme disease coinfection but raised concern that coinfections involving B. duncani may be more common than previously suspected.1
The frequency of B. duncani-Lyme disease coinfection remains uncertain because species-specific testing is not routinely performed in many regions.
Editor’s note: I remain concerned that B. duncani may be underrecognized because it is not routinely included in many diagnostic evaluations in the eastern United States and Canada. Patients with compatible symptoms may therefore go undiagnosed. More independent molecular and public health studies are needed to define its true geographic distribution.
Frequently Asked Questions
What is Babesia duncani?
Babesia duncani is a tick-borne parasite that infects red blood cells and can cause babesiosis. It was formerly called WA1 and was initially associated primarily with the western United States.
What are the symptoms of Babesia duncani?
Symptoms may include fever, chills, sweats, fatigue, headache, body aches, dizziness, shortness of breath, anemia, and low platelet counts. Some infections may be mild or asymptomatic, while others can become severe.
Is Babesia duncani found on the East Coast?
Reports suggest that B. duncani may occur outside the western United States, including parts of Canada and possibly the eastern United States. However, its true East Coast prevalence has not been established.
How is Babesia duncani treated?
Treatment is generally based on regimens used for other forms of babesiosis, such as atovaquone with azithromycin. Laboratory studies suggest that B. duncani may have lower susceptibility to several commonly used medications, but controlled human treatment studies are limited.
Does tafenoquine treat Babesia duncani?
Tafenoquine has shown activity against B. duncani in laboratory and mouse studies, particularly when combined with atovaquone. Human reports have primarily involved relapsing B. microti, so tafenoquine is not yet an established treatment for human B. duncani infection.
Clinical Takeaway
Babesia duncani is a distinct Babesia species that may be more geographically widespread than once believed, although its true distribution remains uncertain. Routine testing may not identify every infection, and laboratory studies suggest it may differ from B. microti in drug susceptibility.
Patients with compatible symptoms should be evaluated using clinical findings, exposure history, laboratory abnormalities, and appropriate Babesia testing rather than geography alone.
Related Articles
These articles provide additional information about Babesia symptoms, diagnosis, treatment, and emerging Babesia species.
Babesia symptoms, diagnosis, and treatment
Case series examines the complexity of Babesia
Different clinical presentations of Babesia
References
- Parveen N, Bhanot P. Babesia microti–Borrelia burgdorferi coinfection. Pathogens. 2019;8(3):117.
- Abraham A, Brasov I, Thekkiniath J, et al. Establishment of a continuous in vitro culture of Babesia duncani in human erythrocytes reveals unusually high tolerance to recommended therapies. J Biol Chem. 2018;293(52):19974-19981.
- Singh P, Lonardi S, Liang Q, et al. Multi-omics analysis of Babesia duncani identifies virulence factors and therapeutic targets. Nat Microbiol. 2023;8(5):845-859.
- Pal AC, Renard I, Singh P, et al. Babesia duncani as a model organism to study development, virulence, and drug susceptibility in vitro and in vivo. J Infect Dis. 2022;226(7):1267-1275.
- Scott JD, Scott CM. Human babesiosis caused by Babesia duncani has widespread distribution across Canada. Healthcare (Basel). 2018;6(2):49.
- Yang Y, Christie J, Köster L, Du A, Yao C. Emerging human babesiosis with “ground zero” in North America. Microorganisms. 2021;9(2):440.
- Levin AE, Krause PJ. Transfusion-transmitted babesiosis: Is it time to screen the blood supply? Curr Opin Hematol. 2016;23(6):573-580.
- Vydyam P, Singh P, Renard I, et al. Tafenoquine-atovaquone combination achieves radical cure and confers sterile immunity in experimental models of human babesiosis. J Infect Dis. 2024;243:125-136.
- Krause PJ, Rogers R, Shah MK, et al. Tafenoquine for relapsing babesiosis: A case series. Clin Infect Dis. 2024;79(1):130-137.
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
Is the test for b. ducani reliable?
I have my concerns. I have not seen reliability data in actual practice.
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.
So weird. I believe I was infected in the state of Washington…in the Chuckanuts(foothills) outside of Bellingham. I didn’t think that, until I was talking to my next door neighbor…he was always working on his landscaping. Suddenly, his yard wasn’t looking as beautiful…we were talking one day. He told me he was dealing with Babesia Duncani, and he was exhausted. I told him I was diagnosed as well. I don’t know where he was tested, but we both seemed to have been infected that same spring. He was using a lot of herbals as the medication recommended did nothing. My situation is that I’m allergic to that whole class of antibiotics used to treat the infection. I was on Malarone for along time, but my last test(I now live in a different state) shows the infection is worse. Not really sure there is anything else that can be done, as long as most medical establishments could care less. Clinics that actually treat Lyme and co-infections around here are shysters.
Babesia Duncani was initially diagnosed on the west coast of the USA. I have patients in USA also test positive for Babesia Duncani. The challenge is to determine if it is a true positive.
Interesting. I always thought LLMD doctors find IGENEX testing the most reliable. I’ve tested positive for Duncani twice. Is it because you don’t know a treatment, that you are challenging their testing methods? Wow! I guess I don’t hold out for healing from this.
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.
I have a similar experience in some patients in my practice.
How are you treating Duncani if Malarone & Mepron dont seem to kick it?
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.
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?
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.
I don’t think anyone knows. The Malarone and antibiotics don’t work. I tried this for a long time, but I’m allergic to the antibiotics that end with “mycin”. In my last IGENEX test this year, the B. Duncani went from 60 to 90, and I have another Borrelia infection called B. Hermsii. if I thought doctors were clueless before, now they are just completely uneducated about these infections.
The tests are not as reliable as I would like no manner who is running them. I find it important to include a reevaluation for another illness
With B. Duncani would you typically find muscle pain/burning, exhaustion and elevated lactate levels (flu like symptoms but no fever)?
I find it hard to be sure what tick borne infection is the cause of symptoms. I also check to make sure another illness is the cause
Henry, Chris,
I had B. duncani and B. burgdorferi for years without fever or any other typical blood indicator of infection. I first tested positive for Babesia by smear then by antibody for B. duncani (after the cure). I was successfully treated with Mepron and Azithromycin but it took several (3) treatments. There is NO reason to be parsimonious with antibiotics when treating tick borne illness so if your doctor has those propensities, find another. When you are cured, you will know it.
How are you doing now Joel? I start treatment tomorrow for same thing
So what is an effective treatment for Babesia Duncani?
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.
Kathleen,
I’m from PA and experienced a very similar situation as you, but that seems to be the norm when dealing with infectious disease specialists and tick borne diseases. I’ve always been really fit and healthy, then some strange things started happening out of nowhere that ramped up over a 3 year period. Then one day I developed severe afib, and was off to the hospital by ambulance. A huge list of other symptoms grew from there (POTS, panic attacks, sweats, palpitations, head pain, unstable BP, tinnitus, air hunger, fevers, vertigo, etc.). I’m not sure how I survived summer 2020. Eventually I came to terms that the medical system wasn’t going to help me, and turned to my own research. I sincerely thank Dr. Daniel Cameron and Dr. Wayne Anderson for putting babesia on my radar, as I had never heard of it before… but their articles made more sense of my symptoms than anything else I was considering (cancer, lupus, MS, brain tumor, etc.). The information they posted may have very well saved my life. My condition progressively worsened, and I was several weeks bedridden before finally starting treatment with an LLMD. Initial IGeneX testing showed positive for Lyme and babesia sp. were visible on blood smear but no microti or duncani antibodies were detected. Within 3 days of starting malarone + azithromycin, I was 50% better and could start walking around the house… and start interacting with my wife and young kids again. Unfortunately, after about 2 months the malarone effectiveness seemed to decrease, and at 4 months it was obviously not working anymore. I was switched to primaquine, hydroxychloroquine, tinidazole (4 days on, 3 days off), and ceftin. I stayed on that combo for 6 months and my issues resolved one by one… and stayed gone. Babesia became undetectable on (>30 minute) blood smear inspections, but repeat IGeneX testing now showed positive IgG antibodies for duncani. The Lyme ImmunoBlot turned negative. New IGeneX testing showed I also have IgM and IgG antibodies to bartonella, and my RTL urine test was highly positive for multiple types of mycotoxins… so I still have some things to deal with. Today I’m feeling about 90% recovered… but some milder head pain, tinnitus, and intermittent vertigo remain. Babesia duncani was my worst infection, and it was a huge fight beating it back. If your ID docs in NH are like the ones in PA… I can’t stress strongly enough the importance of finding a good LLMD.
BTW, my liver was affected by this. I was diagnosed with NAFLD with no plausible explanation. The liver damage even showed up on my first CT scan the day of afib. Follow up testing showed my liver is now completely healed after a year of treating tick borne infections.
I read all of what you wrote and realize this was a year ago that you posted. I am looking for answers for my 17 yr old. Pediatrician is of NO help and I have tested her for EVERYTHING. A tick borne panel was done in Dec of 2021 and showed equivocal results which the pediatrician didn’t blink an eye at. Since then, I have come to know that there is Babesia Microti and Babesia Ducani. She was only tested on the panel for Microti. She has had severe fatigue, weight loss, hair loss, severe hormonal imbalances, panic attacks, headaches…you name it. We are a family that travels to Central America quite often and we live in the Northeast. I am wondering how your gut fared with all of the antibiotics you took and if you ever considered any herbal treatments in lieu of the antibiotic route. Also how were you eventually diagnosed? Was it all thru bloodwork? Reason I am asking is because I am reading that a negative result, does not necessarily mean infection isn’t present. Thank you for any response…….
That is a wild story Dan. I too live in PA and our stories are extremely similar. I was fit and healthy, then got a tick bite one day. Five days later I had the highest fever of my life and almost got hit by a car on my way into the doctor’s office I was so out of it. I told the doctor about the tick bite and was told that I probably have the flu, I had never had the flu in my life at that point and dismissed it, flu test was negative. I then repeated to the doctor that I had pulled a tick off myself five days earlier. He seemed reluctant, but put me on 10 days of doxycycline, and I felt much better very quickly.
Years went by and symptoms started creeping in that I did not understand. Fatigue was the first, I thought I needed more exercise and stricter diet, both of which seemed to make me feel worse. I saw dozens of doctors and got the same ” your bloodwork looks good.” again and again. Then came the chest pain and palpitations, saw a half dozen cardiologists, then boom AFIB and a ambulance ride to the ER. All the symptoms you name and then some over the years, and then finally bed ridden. Fatigue that I can only explain as “If the house were burning down around me, I would just lay there and burn with it.” Finally I met an LLMD that was willing to treat me. It took 3.5 years of treatment and being on 3 antibiotics and an antiparasitic at the same time, but I felt much better, however symptoms would always come and go and I feared they would someday come back, and they have. I am not nearly as bad as I was years ago, but I did not wait and sought treatment from my LLMD before things got out of hand. This time we ran the full tick bourn illness battery of tests, and I was positive for both Lyme and Babesia. I hope with this new information me and my doctor can come up with a good game plan and knock this out for good. It has stolen over a decade of my life, in what is supposed to be my prime, and I am beyond tired of these diseases.
Good luck to all.
How long do you typically treat? I tested positive for B. Duncani recently (Virginia) with no other parasite found. It’s complicated by chronic reactivating EBV. My doctor initially prescribed hydroxychloroquine, atovaquone, and azithromycin (21 days on, 10 days off x 3 cycles). I have found I’m completely intolerant to the hydroxychloroquine, so that’s been removed. Herx is tough on this. Is there anything I should ask in regard to other research? I haven’t found mych except for this site.
I find every patient in my practice challenging. I have not supported pulse or cyclical therapy.
How long do you typically treat? I tested positive for B. Duncani recently (Virginia) with no other parasite found. It’s complicated by chronic reactivating EBV. My doctor initially prescribed hydroxychloroquine, atovaquone, and azithromycin (21 days on, 10 days off x 3 cycles). I have found I’m completely intolerant to the hydroxychloroquine, so that’s been removed. Herx is tough on this. Is there anything I should ask in regard to other research? I haven’t found mych except for this site.
My husband pulled a tick off of him in October. 2 weeks later he scheduled an appt. with his PCP to get a Lyme test. His doctor took a look at him and sent him to the ER, where he was admitted as an inpatient for five days due to the fact he was in liver failure. The second day of his hospital visit I asked the team to test him for babesiosis. After 10 hours of advocating for this test and telling them the test needed to be sent to a speciality lab, the did test him, but in their own lab. His test came back negative.
We have been going through four months of pure hell with his team of doctors dismissing the idea of him having babesiosis, so I purchased a kit from igenex.com. It came back positive for babesia duncani on Feb 23rd. We were finally validated and he was referred to an infectious disease specialist who did not see the specialty lab results, only the initial negative ones, and told us he was sure my husband did not have babesiosis. When he finally received a copy of the positive lab results, he was surprised and wanted to know how my husband “picked up a West coast parasite”. After telling him we did not travel to the west coast and that he was bitten by a tick in our back yard in New Hampshire, he finally prescribed us with the treatment for babesiosis, but STILL thinks the liver failure and the babesiosis are not related.
This has been beyond frustrating and it feels like we are fighting for his life daily and no one will treat this seriously.
I’m just here to share this story and see if anyone else in the NH area has experienced something like this. According to what I have read babesia duncani has been on the East coast since approx. 2018. How are doctors here not up to date on babesiosis??
Kathleen, sorry to hear what you have been up against. I believe that the 2 times I got bit it was on the East coast (I live in CT). I tested positive for both duncani and microti. Seems only LLMD’s like Dr. Cameron are up to date and knowledgeable of this. Sadly, I know not everyone can afford to pay up front (then submit to insurance risking it won’t be covered). But I believe there is a big difference in the treatment you will get from someone Lyme Literate.
Dx with B. Duncani, Bartonella, and Lyme. It’s been over a year with no relief from Chronic Fatigue, Peripheral Neuropathy and Anemia. Been on Zithromax, Mepron, Mamaroneck for 8 weeks and Bactrim for 3 weeks. No improvement, only getting worse. See Hematologist next week.
I tested positive (IgG, Igenex) for B. duncani in 2007 two years after treatment with Mepron. I tested negative (IgG/IgM, Igenex) in 2005 for B. microti but my Lyme doctor treated me anyway. Mepron apparently worked for me; isn’t it the same as Atovaquone?
A blood smear by Lida Mattman’s lab in 2000 showed Babesiosis in my blood cells using elecron microscopy, which doesn’t distinguish between species. I am from Maryland and had been to California one time… in 1985 while serving in the Navy. I attended SERE school in the mountains of SoCal for 1-2 weeks. My babesiosis in 2000 was presumed to be microti; I’d contracted Lyme in 1991 and initially I assumed coinfection at that time with microti. I didn’t get positive Lyme results until 2000 and had successful treatment for both by 2005 but didn’t realize it was duncani until 2007.
thanks for sharing.
I am from NH. My test just came back positive for Babesia duncarni (more recent infection), Anaplasmosis (more recent infection), Bartonella Henselae (old infection), and Borrelia Burgdorferi (old infection). This was my first time having a Lyme test because of all of the strange and frustrating symptoms I have been dealing with. It is concerning to know that my system is dealing with all of these infections at once. We are treating the Babesia first with Atovaquone and azithromycin for 10 days, and then we are going to switch to herbal approach, possible UV blood treatment, and also tackle the other infections. I am wondering if the other infections make it more difficult to find complete resolution of Babesia and vice versa. Thoughts/experiences?
My 35 yo daughter has had Lyme disease and Babesia Duncani for over 15 years verified by testing with IGENX. The Lyme disease shut down her digestive system and she has been on TPN since then. She is using IV Clindamycin and Quinine as a treatment for the Babesia which helps but does not cure. We flew from FL many years ago to see you in NY but you said at that time you could not help her. Since then her hemoglobin can drop very fast and she has had over 250 units of blood so far. After a blood exchange she went 5 years without needing a transfusion but then recently started needing them again. Her hemotologist does not understand this disease and doesn’t want to do another blood exchange even though the previous one, which was authorized by his PA when he was out of town, helped so much. My daughter’s PCP believes this would help her but the hemotologist refuses, saying there is no hemolysis in her blood when her Hgb drops so he won’t do it. I don’t know why this is the case but wish someone who is studing this disease would take an inerest and find out why so they can help her and others who might have this unusual symptom.