Treponema pallidum haemagglutination test for yaws. Comparison with the TPI and FTA-ABS tests.

Similar antibodies are produced in the serum of patients infected with the pathogenic treponemes T. pallidum and T. pertenue, and for this reason sera from persons with syphilis or yaws react similarly in the conventional tests for syphilis and in the Treponema pallidum immobilization (TPI) and fluorescent treponemal antibody absorption (FTAABS) tests. In the TPI and FTA-ABS tests T. pallidum is used as antigen, and these tests are regarded as specific for treponemal infection. The Treponema pallidum haemagglutination (TPHA) test is the latest addition to this group of specific tests. The TPI test is generally accepted as the most specific test for treponemal infection. However, because of its complexity, its performance is limited to comparatively few laboratories. A specific test is therefore required which has an acceptable sensitivity and specificity and which can be carried out without undue expense. The pathogenic and non-pathogenic commensal treponemes induce some common or group antibodies, most of which can be removed from serum by absorption with an extract of Reiter treponemes. In the FTA-ABS test this is achieved by the use of sorbent and in the TPHA test by including components of Reiter treponemes in the absorbing diluent. Kiraly, Jobbaigy, and Kovats (1967) showed that Reiter treponemes do not always remove all group antibody from serum, and that this was the cause of most borderline and non-specific FTA-ABS test results. It would be reasonable to expect a similar effect in the TPHA test, but this has not been reported so far. The TPHA test is available commercially in kit form. It is simple to perform and read, and requires no expensive equipment. It was found to be equal in specificity and sensitivity to the FTA-ABS test on syphilitic sera (Gamer, Backhouse, Daskalopoulos, and Walsh, 1972) and was considered to be an acceptable alternative to the FTA-ABS test.