Enzyme-Linked Immunosorbent Assay; (ELISA)
The ELISA test is potentially the most useful serological test (Ellis, 1986a). This test is highly sensitive, easy to perform and can measure IgM and IgG antibody levels in serum without prior fractionation, by using specific anti-IgM and anti-IgG enzyme conjugates (Adler et al., 1981; Cousins et al., 1985; Thiermann and Handsaker, 1985).
It has a number of advantages over the MAT. It uses a killed antigen; results can be read objectively rather than subjectively, and it can measure different immunoglobulin classes without prior fractionation of sera (Cousins et al., 1985). The ELISA test is much more accurate than the other serological tests and has many advantages from the point of view of laboratory practice (Thiermann and Garrett, 1983; Cho et al., 1989). Some difficulty is encountered in interpreting the significance of titres of antibody in serum. Although there is no marked difference between vaccinal and infection titres (Trubea et al., 1990), it is apparent from a heifer trial that infection titres generally persist much longer (Broughton et al., 1984).
Because the ELISA technique can be readily scaled up to test many samples, it would be particularly useful for epidemiological studies. The high level of sensitivity, and specificity obtained for the ELISA-IgG, indicated that this test would be a good alternative to the MAT for detection of leptospirosis (Cousins et al., 1986).