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Babesia is a group of tick-borne protozoal parasites under the order Piroplasmida. They are found around the world. Over the years, there has been some rearrangement of the taxonomy. What was once considered one genus has been rearranged several times and is now considered to be closely related to other genera like Theileria. Babesia species tend to be host-specific and more than 100 species have been identified globally. Babesiosis (Babesia bigemina) was first discovered in cattle in 1888 and the first human case (most likely B. divergens) was identified in 1957.
A third Babesia species in humans… and maybe a fourth?
The two species that were known to infect humans are quite genetically distinct from the rest of the order. B. microti is the top species causing human infections in the US, while B. divergens is the top species causing infections in Europe. While some people can experience severe illness and death, many have asymptomatic infections. In areas of the US Northeast, as many as 25% of people are seropositive (have antibodies) for Babesia.
A third emerging species in human infection is B. duncani, found in the US Northwest. B. duncani has added some mystery to the Babesia story because it has never been isolated from ticks, animals, or people west of the Rocky Mountains. However, as it has been added to serology panels, people in the US Northeast have been testing positive for antibodies against B. duncani. What does this mean? Are these people being exposed to B. duncani when traveling in the Western states? Or is there another genetically similar and yet unidentified species that is resulting in cross-reactive, false positive results? New discoveries like B. odocoilei recently documented in two humans in Canada also raise the question about the potential for cross-reactivity in antibody test results. Scientists continue to work on this puzzle.
Babesia species expanding in range
A variety of reports over the last three years have found Babesia species linked to human infection in new regions around the world:
| Finding: | See more: |
| B. microti endemic to certain US states has expanded to include Maine, New Hampshire and Vermont | Swanson, M. et al. (2023, March 17). Trends in reported babesiosis cases – United States, 2011-2019. Morbidity and Mortality Weekly Report, 72(11), 273-277. http://dx.doi.org/10.15585/mmwr.mm7211a1 https://www.cdc.gov/mmwr/volumes/72/wr/mm7211a1.htm |
| B. odocoilei found in sick humans in Canada, with expanding range of detection in Canada | Scott, J. D. et al. (2021). Detection of Babesia odocoilei in humans with babesiosis symptoms. Diagnostics (Basel), 11(6), Article 947. https://doi.org/10.3390/diagnostics11060947 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8228967/ |
| B. microti found in small mammals for the first time in South America | Santodomingo, A. M. et al. (2022). Apicomplexans in small mammals from Chile, with the first report of the Babesia microti group in South American rodents. Parasitology Research, 121(3), 1009-1020. https://doi.org/10.1007/s00436-022-07452-4 https://pubmed.ncbi.nlm.nih.gov/35102466 |
| Second babesiosis case ever identified in India | Godbole, R. et al. (2022). Case report: A fatal case of babesiosis in a splenectomized male patient from Western India. American Journal of Tropical Medicine and Hygiene, 106(5), 1421-1425. https://doi.org/10.4269/ajtmh.20-1118 https://pubmed.ncbi.nlm.nih.gov/35189595 |
| B. microti found in a tick is first report of the pathogen in Israel | Mumcuoglu, K. Y. et al. (2022). Pathogens in ticks collected in Israel: II. Bacteria and protozoa found in Rhipicephalus sanguineus sensu lato and Rhipicephalus turanicus. Ticks and Tick-borne Diseases, 13(5), Article 101986. https://doi.org/10.1016/j.ttbdis.2022.101986 https://pubmed.ncbi.nlm.nih.gov/35816829 |
Developments in Babesia affecting animals
Reports in animals also indicate an expanding range of Babesia species and present challenging One Health risks:
| Finding: | See more: |
| First recorded fatal case in a cat of B. canis, a species that prefers dogs | Remesar, S. et al. (2022). A case report of fatal feline babesiosis caused by Babesia canis in north western Spain. BMC Veterinary Research, 18(1), Article 177. https://doi.org/10.1186/s12917-022-03287-4 https://pubmed.ncbi.nlm.nih.gov/35568873/ |
| Rhinoceros sickened by B. bicornis. Rhinoceros are generally asymptomatic carriers unless stressed. | Zimmermann, D. E. et al. (2022). Successful treatment of babesiosis in a south-western black rhinoceros (Diceros bicornis bicornis). Journal of the South African Veterinary Association, 93(2), 139-143. https://doi.org/10.36303/JSAVA.478 https://pubmed.ncbi.nlm.nih.gov/35934911/ |
| Isolated deer species infected with novel Babesia species. Moving these deer for conservation risks spreading the Babesia species. | Santodomingo, A. et al. (2022). A search for piroplasmids and spirochetes in threatened pudu (Pudu puda) and associated ticks from Southern Chile unveils a novel Babesia sp. and a variant of Borrelia chilensis. Transboundary and Emerging Diseases, 69(6), 3737-3748. https://doi.org/10.1111/tbed.14743 https://pubmed.ncbi.nlm.nih.gov/36317891/ |
| Babesia species found in a variety of animal species and seem to be species-preferential, like those that infect dogs and humans. | Lee, S. et al. (2022). Evolutionary analysis of Babesia vulpes and Babesia microti-like parasites. Parasites & Vectors, 15, Article 404. https://doi.org/10.1186/s13071-022-05528-9 https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-022-05528-9 |
Prevention and treatment
No great advances in the prevention and treatment of babesiosis have been reported over the last few years, though scientists have steadily increased their knowledge about the parasite and its potential vulnerabilities.
Prevention rests primarily on avoidance of tick bites. Of note, a 5-year field trial vaccinating mice against Borrelia burgdorferi found decreased prevalence of Babesia microti as well.
Diagnostics are more important than ever
Meanwhile, this brings home yet again the value of direct detection to make a correct clinical diagnosis. While B. microti and B. divergens tend to have well-established clinical guidance, not much is known about the clinical importance of B. duncani or B. odocoilei for human infection at this point.
The mystery of positive B. duncani serology tests in the US Northeast demonstrates the importance of direct detection. The development of better therapeutics also requires accurate species identification and isolation.
Find out more about Galaxy Diagnostics PCR testing for Babesia/Theileria species.
In addition to the testing Galaxy Diagnostics currently offers, we are continually working to apply the technology that we currently use on Bartonella and Borrelia species to Babesia species testing. This includes technology such as ddPCR that completes more than 20,000 PCR tests on each sample, improving detection of low-abundance infections.
Galaxy Diagnostics scientists are also working on understanding emerging Babesia species that are infecting humans. All of this work on technology and species-specific science leads to developing diagnostics with the most utility for the diagnosis and treatment of the people impacted by these pathogens.
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Vannier, E. et al. (2023). Deployment of a reservoir-targeted vaccine against Borrelia burgdorferi reduces the prevalence of Babesia microti coinfection in Ixodes scapularis ticks. Journal of Infectious Diseases, 227(10), 1127-1131. https://doi.org/10.1093/infdis/jiac462 https://pubmed.ncbi.nlm.nih.gov/36416014/
