Incidence of positive serologic tests for treponemal infection in healthy rabbits

Sera from 167 apparently normal rabbits were screened by the Venereal Disease Research Laboratory (VDRL) slide test and by the fluorescent treponemal antibody-absorption (FTA-Abs) and microhemagglutination assay for Treponema pallidum antibodies (MHA-TP) test. Three sera (1.8%) were reactive in all three tests, a fact suggesting possible inapparent infection with Treponema paraluis-cuniculi. One hundred forty-four sera (86.2%) were nonreactive in all tests. The VDRL slide test was reactive with 22 sera (13.2%). In 19 of these, treponemal tests were nonreactive; thus the rabbits probably were not infected with pathogenic treponemes. One hundred sixty-three sera (97.6%) were nonreactive in both treponemal tests, and three sera (1.8%) were reactive in both. One serum was reactive in the FTA-Abs test and nonreactive in the MHA-TP test. The lower incidence of reactivity with treponemal tests suggests that the FTA-Abs and MHA-TP tests are more useful than the VDRL slide test for screening rabbits intended for experimental studies of syphilis.