A modified IF-test to demonstrate IgM antibodies to Babesia divergens of cattle.

An IF–test modified to increase sensitivity was used to detect the presence of Babesia divergens specific IgM antibodies. It consisted of three steps: (1) the incubation of Babesia antigen with test serum, followed by; (2) its incubation with protein A; and (3) the addition of rabbit anti-bovine IgM bound to protein A, which was bound with FITC. Compared to the conventional IF–technique, this modified IF-technique detected bovine anti-Babesia-IgM in test serum at a two–fold lower dilution and with a diminished background staining. This modified IF-technique improves the possibilities for studying class Μ antibody in the serum of cattle which have been infected with B. divergens. It is possible to determine whether a calf s antibody response is due to maternally transmitted antibodies or actively acquired antibodies by determining the presence of each of the classes of immunoglobulin against B. divergens present in the calf s serum.