SEROLOGICAL DIAGNOSIS OF OVINE ENZOOTIC ABORTION BY COMPARATIVE INCLUSION IMMUNOFLUORESCENCE ASSAY, RECOMBINANT LIPOPOLYSACCHARIDE ENZYME-LINKED-IMMUNOSORBENT-ASSAY, AND COMPLEMENT-FIXATION TEST

Since the 1950s, serological diagnosis of ovine enzootic abortion (OEA ), caused by strains of Chlamydia psittaci, has been based mainly on t he complement fixation test (CFT), which is neither particularly sensi tive nor specific since antibodies to other chlamydial and enterobacte rial pathogens may be detected, In this study, a recombinant enzyme-li nked immunosorbent assay (rELISA) (medac, Hamburg, Germany), based on a unique chlamydial genus-specific epitope of Chlamydia trachomatis L2 lipopolysaccharide, was evaluated for sensitivity and specificity as a primary screening assay for OEA by comparison with the CFT, A compar ative inclusion immunofluorescence assay (IFA), in which antibody tite rs to C. psittaci and Chlamydia pecorum were examined, was used as the reference test for 573 serum samples from four flocks, Reactivity to C. pecorum was measured since inapparent intestinal infections by C. p ecorum are believed to be common in British flocks, In detecting posit ive sera from an abortion-affected flock, in which a C. pecorum infect ion was also suggested by IFA, the rELISA outperformed the CFT with si gnificant evidence for increased sensitivity (P = 0.003), In two flock s in which C. pecorum infections alone were suggested by IFA, the rELI SA and CFT were prone to detect low levels of false-positive results, but the values were not significant, The rELISA provided results in on e flock in which sera that were anticomplementary could not be resolve d by the CFT, In another hock in which abortion had not occurred but i nfection by both chlamydial species was suspected, no significant diff erence was found between the sensitivities of the rELISA and CFT, The rELISA could not differentiate ovine C. psittaci and C. pecorum infect ions but was shown to be a more sensitive primary screening test for O EA than was the CFT, particularly where abortion had occurred and even when antibodies due to additional inapparent infection(s) by C. pecor um were present.