Babesiosis is an emerging, tick-transmitted zoonotic disease caused by hematotropic intraerythrocytic parasites of the genus Babesia, commonly termed piroplasms due to their pear-shaped forms within red blood cells [2][3]. The infection is transmitted principally by ixodid ticks and may also occur through blood transfusion, transplacental passage, or organ transplantation [3].
Disease overview
Parasitic Evidence-backed information EN 5/7 applicable sections · ZH 5/7 applicable sections Updated Oct 23, 2026
Babesiosis is a globally emerging tick-borne parasitic disease with rising frequency and expanding geographic distribution [1][2][3]. It poses a notable health burden particularly among immunocompromised persons and those infected via blood transfusion, with mortality reaching up to 20 percent in these groups [1]. Human cases occur worldwide but are most concentrated in the northeastern and upper midwestern United States [3].
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The disease displays a broad clinical spectrum, from silent infection to a severe malaria-like illness with marked hemolysis that can be fatal [2][3]. In immunocompromised and older patients, babesiosis carries heightened risk of severe outcomes [3]. Parasites are identifiable as typical intraerythrocytic forms on thin blood smear or by detection of Babesia DNA using PCR [1][3].
Babesiosis is an increasingly frequent worldwide emerging disease with growing endemic range and substantial burden, especially among immunocompromised and transfusion-acquired cases [1]. Human infection is globally distributed but incidence is highest in the northeastern and upper midwestern United States, with regional species variation such as B. microti in the US and B. divergens in Europe [2][3]. Improved diagnostic sensitivity has enabled more accurate epidemiological characterization [2].
The parasites are transmitted primarily by ixodid ticks and are maintained in nature through infection of diverse vertebrate hosts [2][3]. Less common routes include blood transfusion, transplacental transmission, and organ transplantation [3].
Personal and community-level protective measures against tick exposure can reduce the overall infection burden, though such approaches are unlikely to halt continued expansion of Babesia into previously non-endemic areas [1].
- 1 Krause PJ et al. Human babesiosis. Int J Parasitol. 2019 Feb. PMID: 30690090. doi: 10.1016/j.ijpara.2018.11.007. PubMed: https://pubmed.ncbi.nlm.nih.gov/30690090/
- 2 Homer MJ et al. Babesiosis. Clin Microbiol Rev. 2000 Jul. PMID: 10885987. doi: 10.1128/CMR.13.3.451. PubMed: https://pubmed.ncbi.nlm.nih.gov/10885987/
- 3 Waked R et al. Human Babesiosis. Infect Dis Clin North Am. 2022 Sep. PMID: 36116841. doi: 10.1016/j.idc.2022.02.009. PubMed: https://pubmed.ncbi.nlm.nih.gov/36116841/
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