How to Detect Antibodies Against Babesia divergens in Human Blood Samples

Abstract

Background Today only indirect fluorescent antibody assays (IFA) are commercially available to detect antibodies against Babesia divergens in humans. IFA is subjective and requires highly experienced staff. We have therefore developed an ELISA-based method for measuring anti-B. divergens IgG-antibodies in human blood samples. Methods Crude merozoite extract from in vitro cultures of a new B. divergens isolate was used in ELISA to detect antibodies in different sets of samples: Borrelia burgdorferi-positive samples, healthy individuals, tick-bitten individuals including follow-up samples 3 months later, positive control samples from patients with an active Babesia infection and samples from malaria-endemic regions. As a reference, IFA was used to detect antibodies in the tick-bitten samples. Western blot was used to evaluate reactions against specific bands in extracts with/without parasites. Results Using IFA as reference method, the sensitivity and specificity of the ELISA was 86% (12/14) and 100% (52/52). There was a very high correlation (r = -0.84, p = 0.0004) between IFA dilution factors and ELISA absorbances among the samples classified as positive. 5% of the B. burgdorferi-positive samples were judged as weakly positive and 5% as strongly positive in our ELISA.Western blot showed that the immunodominant antigens (around 120 kDa) were from merozoites and not from erythrocytes. Conclusions This ELISA can detect antibodies directed against B. divergens, and it can be a useful and easy assay to handle compared to IFA. The ELISA can also measure high and low levels of antibodies, which could give insight into the recency of a B. divergens infection.