Field evaluation of a new commercially available ELISA based on a recombinant antigen for diagnosing Chlamydophila abortus (Chlamydia psittaci serotype 1) infection

A new commercially available ELISA (ELISAr-Chlamydia) for detecting antibod ies against Chlamydophila abortus has been evaluated using sheep field seru m samples. The ELISA is based on a recombinant antigen which expresses part of a protein from the 80-90 kDa family that is specific to C. abortus. Ser a (105) from six flocks with confirmed ovine chlamydial abortion (OEA) outb reaks were used in this study, as well as sera (258) from 18 flocks which h ad suffered no OEA in the last lambing. The ELISAr-Chlamydia was compared w ith the complement fixation test (CFT) and with an ELISA using purified C. abortus elementary bodies (ELISA-EB), employing as reference technique a co mparative microimmunofluorescence test that differentiates C. abortus infec tion from Chlamydophila pecorum infection. The results showed that the sens itivity of ELISAr-Chlamydia was 90.9% with a specificity of 85.9%, the sens itivity of CFT was 71.0% with a specificity of 83.6%, while the sensitivity of ELISA-EB was 95.2% and the specificity was 54.2%. Furthermore, ELISAr-C hlamydia was the test with fewer false positives resulting from positive re activity to C. pecorum, although 15% of the sera positive for C. pecorum bu t negative for C. abortus antibodies reacted positively. This study demonst rated with field material that ELISAr-Chlamydia provides the most balanced results between sensitivity and specificity, especially in hocks with no cl inical OEA but reactivity to C. abortus. (C) 2001 Elsevier Science B.V. All rights reserved.