Effect of anti-immunoglobulin antibodies produced in cattle infected with Trypanosoma evansi on antigen detection ELISA.

The possibility of interference with the antigen-detection ELISA for trypanosomosis by anti-rodent IgG antibodies produced in cattle infected with Trypanosoma evansi was investigated. Two different ELISA for detection of trypanosome antigen and three different systems for anti-rodent IgG antibody detection were established. The former two were respectively polyclonal antibody-based and a combination of monoclonal and polyclonal antibody-based assays. The latter three were also adapted for detection of anti-mouse IgG, anti-rabbit IgG and anti-IgG antibodies cross-reactive with both rabbit and mouse IgGs. A total of 170 samples were collected from a dairy cattle farm where an outbreak of T. evansi infection was reported. One hundred and two cattle (59%) were found to be positive for trypanosome antigens by the polyclonal antibody-based assay and 86 (51%) were positive by the combination-based system. On the other hand, 51 (30%) and 10 (6%) of cattle had anti-rabbit and anti-mouse IgG antibodies respectively but none had antibodies cross-reactive with both IgGs. Of the 102 cattle positive for trypanosome antigens in the polyclonal antibody-based ELISA, 48 (47%) were also anti-rabbit IgG antibody positive. It is concluded that antigen detection ELISA based on a single-species immunoglobulin for capture and detection might misdiagnose T. evansi infection. Results indicate that this bias will be avoided if reagents for capture and detection are derived from different species.