Observations on the use of ELISA for detection of Babesia bigemina specific antibodies

An indirect enzyme-linked immunosorbent assay (ELISA) was evaluated to study the cause of the high level of background reactions which hinders the application of ELISA as a field diagnostic test for Babesia bigemina. Different blockers to improve the specificity of the ELISA were compared. THe use of soya milk (25%), gelatin (2.5%) and chicken serum (2%) did not significantly improve the specificity of the test. It was noted that the presence of fibrinogen contributed to the positive ELISA results more than the presence of B. bigemina specific antigen. This conclusion was confirmed by testing bovine fibrinogen as a host protein antigen in ELISA which strongly responded against B. bigemina positive control sera. It is suggested that application of ELISA for B. bigemina is still unreliable until a more purified Babesia-specific antigen or specific monoclonal antibodies are available.