RESUMEN
OBJECTIVES: Human babesiosis is an emerging and potentially fatal tick-borne disease caused by intraerythrocytic parasites of the Babesia genus. Among these, Babesia duncani is particularly notable for causing severe and life-threatening illness in humans. Accurate diagnosis and effective disease management hinge on the detection of active B. duncani infections. While molecular assays are available to detect the parasite in blood, a reliable method for identifying biomarkers of active infection remains elusive. METHODS: We developed the first B. duncani antigen capture assays, targeting two immunodominant antigens, BdV234 and BdV38. These assays were validated using established in vitro and in vivo B. duncani infection models, and following drug treatment. RESULTS: The assays demonstrated no cross-reactivity with other species such as B. microti, B. divergens, Babesia MO1, or Plasmodium falciparum, and can detect as few as 115 infected erythrocytes/µl of blood. Screening of 1731 blood samples from various biorepositories, including samples previously identified as Lyme and/or B. microti-positive, as well as new specimens from wild mice, revealed no evidence of B. duncani infection or cross-reactivity. CONCLUSIONS: These assays hold significant promise for various applications, including point-of-care testing for the early detection of B. duncani in patients, field tests for screening reservoir hosts, and high-throughput screening of blood samples intended for transfusion.
RESUMEN
Human babesiosis is a rapidly emerging and potentially fatal tick-borne disease caused by intraerythrocytic apicomplexan parasites of the Babesia genus. Among the various species of Babesia that infect humans, B. duncani has been found to cause severe and life-threatening infections. Detection of active B. duncani infection is critical for accurate diagnosis and effective management of the disease. While molecular assays for the detection of B. duncani infection in blood are available, a reliable strategy to detect biomarkers of active infection has not yet been developed. Here, we report the development of the first B. duncani antigen capture assays that rely on the detection of two B. duncani -exported immunodominant antigens, BdV234 and BdV38. The assays were validated using blood samples from cultured parasites in human erythrocytes and B. duncani -infected laboratory mice at different parasitemia levels and following therapy. The assays display high specificity with no cross-reactivity with B. microti , B. divergens , Babesia MO1, or P. falciparum. The assay also demonstrates high sensitivity, detecting as low as 115 infected erythrocytes/µl of blood. Screening of 1,731 blood samples from diverse biorepositories, including previously identified Lyme and/or B. microti positive human samples and new specimens from field mice, showed no evidence of B. duncani infection in these samples. The assays could be useful in diverse diagnostic scenarios, including point-of-care testing for early B. duncani infection detection in patients, field tests for screening reservoir hosts, and high-throughput screening such as blood collected for transfusion. Short summary: We developed two ELISA-based assays, BdACA38 and BdACA234, for detecting B. duncani , a potentially fatal tick-borne parasite causing human babesiosis. The assays target two immunodominant antigens, BdV234 and BdV38, demonstrating high specificity (no cross-reactivity with other Babesia species or Plasmodium falciparum ) and sensitivity (detecting as low as 115 infected erythrocytes/µl). The assays were validated using in vitro-cultured parasites and infected mice. Screening diverse blood samples showed no evidence of B. duncani active infection among 1,731 human and field mice blood samples collected from the north-eastern, midwestern, and western US. These assays offer potential in diverse diagnostic scenarios, including early patient detection, reservoir animal screening, and transfusion-transmitted babesiosis prevention.