Human Babesiosis Caused by Babesia odocoilei: An Emerging Zoonosis

Abstract

Human babesiosis caused by Babesia odocoilei has an innate ability to survive in humans. Babesia odocoilei, a sequestered Babesia sp. has unique survival mechanisms to occlude capillaries and venules by forming fibrin-bonded entanglements. Immune evasion has been mastered, and establishment of persistent infections promote survival. Because B. odocoilei sequesters, this tick-borne zoonosis is recalcitrant to treat.

Short Communication

An emerging tick-borne zoonotic disease called human babesiosis caused by Babesia odocoilei is widely distribut­ed in North America. This piroplasmid, a single-celled, red blood cell parasite causes a multitude of insidious symptoms in humans. This microscopic hemoparasite is commonly transmitted by a B. odocoilei-infected Ixodes tick, but can be transmitted by blood transfusion, organ transplantation, and congenital transmission.

Tick vectors include the western blacklegged tick, Ixodes pacificus and the blacklegged tick, Ixodes scapularis. Mamma­lian reservoirs are primarily cervids (i.e., white-tailed deer, Odocoileus virginianus; black-tailed deer, Odocoileus hemio­nus columbianus), but desert bighorn sheep, Ovis canadensis nelsoni, also harbour B. odocoilei [1]. The first-ever discov­ery of B. odocoilei in humans was made by Scott et al. [2]. In Canada, B. odocoilei has been detected in three tick species (i.e., Ixodes angustus, Ixodes pacificus, and Ixodes scapularis) continent wide [3]. Scott and colleagues found that the ratio of B. odocoilei to Babesia microti in I. scapularis adults is 60 to 1 [3]. Babesia odocoilei is, undeniably, the predominant Babesia sp. across North America. Based on testing 224 Ix­odes ticks, researchers found that people are just as likely to contract human babesiosis as Lyme disease [3]. In fact, the Canada-wide prevalence of B. burgdorferi and B. odocoilei in I. scapularis adults was 40% and 36%, respectively [3]. In B.C., a person is pathologically more likely to be bitten by a B. odocoilei-positive Ixodes tick than a B. burgdor­feri-positive Ixodes tick [3,4].

Migratory songbirds play an integral role in the wide dis­persal of I. scapularis larvae and nymphs. Ixodes scapularis harbour at least six tick-borne zoonotic pathogens that in­fect humans [4]. In the spring, northward-bound songbirds transport ticks into Canada from as far south as the neo­tropics and, alternatively, in the fall, southward-migrating songbirds transport ticks to southern latitudes. In Canada, the predominant pathogens that are transmitted to humans are B. burgdorferi and B. odocoilei [3]. Based on a tick-host-pathogen study, researchers detected five tick-borne zoo­notic pathogens in the blood of songbirds [5]. As well, five pathogens have been detected in several studies [3,6]. Ba­besia odocoilei and B. burgdorferi were the most prominent pathogens [6]. When walking in forest and grassy habitat, it is just as likely for a juvenile I. scapularis to be infected with B. odocoilei (human babesiosis) as B. burgdorferi (Lyme dis­ease) [3].

When a B. odocoilei-infected I. scapularis takes a blood meal, it spews sporozoites into the blood stream, and they quickly circulated throughout the body. Fibrinogen in the blood converts to fibrin, and adheres to the tubular endothe­lium (cytoadhesion), and clogs in capillaries and post-cap­illary venules (sequestration) [7,8]. Pathologically fibrin encompasses both infected Red Blood Cells (iRBCs) and un­infected Red Blood Cells (uRBCs) [7,8]. These 3 components form fibrin-bonded entanglements that block capillaries and venules, especially in the brain that have the smallest cap­illaries. Sequestering Babesia species (i.e., B. bovis, B. canis, B. odocoilei) can complete their life cycle within fibrin-bond­ed entanglements and, thus, trophozoites and merozoites remains isolated from the circulatory immune system and spleen [9]. Immune evasion is ostensible. For babesial sur­vival, iRBCs, iRBCs and fibrin form occlusions, and self-per­petuate life within these entanglements. As cytoadhesion progresses and sequestration builds (using mature babesial stages) [7], B. odocoilei has an exceptional means to avoid splenic clearance [9]. In contrast, non-sequestering Babesia (i.e., B. microti) allow the immune system, which consist of microphages, to function normally, and the spleen typically traps and destroys babesial merozoites. Subsequently, pa­tients with B. microti are normally much easier to treat suc­cessfully.

Common Symptoms

Because fibrin-bonded entanglements occlude capillar­ies and venules, oxygen and nutrient are greatly reduced. As B. odocoilei propagates, a multitude of symptoms develop, including unyielding fatigue, cognitive impairment, perpet­ual inflammation (especially in legs at night), restless legs, brain fog, anxiety, delirium/disorientation, nightmares, pro­found wild dreams, disorientation, difficulty remembering, progressive dementia, dizziness, memory loss, muscle and joint stiffness, muscle and joint aches, clumsiness, poor balance, unsteady gait, bladder disfunction, intestinal prob­lems, constipation, sleep disturbance, insomnia, sweats (es­pecially at night), irritability/rage/aggression, irritability, ischemia (slow blood flow), chills, heat and cold intolerance, pathogen-induced depression, air hunger, longstanding headaches, encephalopathy, and Jarisch-Herxheimer reac­tion (herxing). Of particular note, human babesiosis caused by B. odocoilei inflict major depression in the population. A comorbidity, such as human babesiosis caused by B. odocoil­ei and Lyme disease caused by B. burgdorferi s.l. can cause pain and suffering.

As B. odocoilei advances, patients show severe clinical signs and symptoms. Patients can become bedridden and disabled as manifestations progress. As these symptoms de­velop, patients can be suicidal/homicidal and, in some cases, can have fatal outcomes [3]. As fibrin-bonded entanglements of B. odocoilei occlude capillaries and venules, children often become non-verbal, develop muscle weakness, and have un­steady gait. Moreover, children often have bladder and bowel dysfunctional. In particular, B. odocoilei is a sequestering Ba­besia that is recalcitrant to treat [3]. In contrast, B. microti, is a non-sequestering Babesia sp. that is typically less difficult to treat. However, B. odocoilei has developed highly effective mechanism for parasite survival in humans. Deer culls are needed to reduce human babesiosis caused by B. odocoilei. Tick repellants are efficacious. Since people spend consid­erable time in the outdoors, healthcare professionals must acquire continuing medical education in tick-borne zoonotic diseases.

Acknowledgement

None.

Conflict of Interest

None.

References

• Thomford JW, Conrad PA, Boyce WM, Holman PJ, Jessop DA et al., (1993) Isolation and in vitro cultivation of Babesia parasites from free-ranging desert bighorn sheep (Ovis canadensis nelsoni) and mule deer (Odocoileus hemionus) in California. J Parasitol 79(1): 77-84.
• Scott JD, Sajid MS, Pascoe EL, Foley JE (2021) Detection of Babesia odocoilei in humans with babesiosis symptoms. Diagnostics 11(6): 947.
• Scott JD, Scott CM (2024) Molecular detection of Borrelia burgdorferi sensu lato, Borrelia miyamotoi, Babesia odocoilei, Babesia microti and Anaplasma phagocytophilum in Ixodes ticks collected across Canada. J Biomed Res Environ Sci 5(1): 1321-1337.
• Scott JD, Scott CM (2023) Primary detection of the establishment of blacklegged ticks, Ixodes scapularis, in British Columbia, Canada. J Biomed Res Environ Sci 4(1): 935-941.
• Scott JD, McGoey E, Morales A, Pesapane RR (2022) Molecular detection of Anaplasma phagocytophilum, Babesia odocoilei, Babesia species and Borrelia burgdorferi sensu lato in songbirds. J Biomed Res Environ Sci 3(1): 1451-1459.
• Scott JD, Pesapane RR. (2021) Detection of Anaplasma phagocytophilum, Babesia odocoilei, Babesia , Borrelia burgdorferi sensu lato, and Hepatozoon canis in Ixodes scapularis ticks collected in eastern Canada. Pathogens 10(10): 1265.
• Wright IG (1972) An electron microscopic study of intravascular agglutination in the cerebral cortex due to Babesia argentina Int J Parasitol 2(2): 209-205.
• Schetters TP, Kleuskens J, Scholtes N, Gorenflot A (1998) Parasite localization and dissemination in the Babesia-infected host. Ann Trop Med Parasitol 92(4): 513-519.
• Allred DR, Al-Khedery B (2004) Antigenic variation and cytoadhering in Babesia bovis and Plasmodium falciparum: different logics achieve the same goal. Mol Biochem Parasitol 134(1): 27-35.