Since the 1950s, serological diagnosis of ovine enzootic abortion (OEA), caused by strains of Chlamydia psittaci, has been based mainly on the complement fixation test (CFT), which is neither particularly sensitive nor specific since antibodies to other chlamydial and enterobacterial pathogens may be detected. In this study, a recombinant enzyme-linked 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 comparative inclusion immunofluorescence assay (IFA), in which antibody titers 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. pecorum are believed to be common in British flocks. In detecting positive sera from an abortion-affected flock, in which a C. pecorum infection was also suggested by IFA, the rELISA outperformed the CFT with significant evidence for increased sensitivity (P ؍ 0.003). In two flocks in which C. pecorum infections alone were suggested by IFA, the rELISA and CFT were prone to detect low levels of false-positive results, but the values were not significant. The rELISA provided results in one flock in which sera that were anticomplementary could not be resolved by the CFT. In another flock in which abortion had not occurred but infection by both chlamydial species was suspected, no significant difference was found between the sensitivities of the rELISA and CFT. The rELISA could not differentiate ovine C. psittaci and C. pecorum infections but was shown to be a more sensitive primary screening test for OEA than was the CFT, particularly where abortion had occurred and even when antibodies due to additional inapparent infection(s) by C. pecorum were present.
The development of the antibody response to peptides of the transmembrane glycoprotein of bovine immunodeficiency virus (BIV) was followed over a period of 50 weeks in six cattle experimentally infected with the BIV FL112 isolate. Antibody was detected by an enzyme immunoassay using either a linear or a cyclized peptide with structural features common to an immunodominant region of other lentiviruses. The assay was specific for BIV, detecting antibody in bovine sera to BIV FL112 or BIV R29 but not to six other common viruses of cattle. Antibody was present in the sera of all cattle inoculated with BIV FL112 within 4 weeks of infection, peaked between 10 and 30 weeks and persisted in most cattle during the 50 weeks of observation. These features indicate that this assay may be useful in identifying cattle infected with other strains of BIV in the field.
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