Comparison of ELISA and CFT assays for Chlamydophila abortus antibodies in ovine sera.
OBJECTIVE
To compare the sensitivity and specificity of Chlamydophila abortus antibody assays, to find a suitable serological assay for testing sheep for export.


METHODS
Comparison of results from known positive and negative sheep populations.


METHODS
Fifty-five positive and fifty negative sera were analysed by four enzyme linked immunosorbent assays (ELISA), three using recombinant antigens based on the chlamydial polymorphic outer membrane proteins (POMP90-3, POMP90-4, POMP80-90) and one using a synthetic peptide based on chlamydial major outer membrane proteins (MOMP-P). They were also analysed by complement fixation tests (CFT) using crude antigens from chlamydia isolated from an Australian sheep, a Californian parakeet and a Texan turkey. Assay sensitivity and specificity were expressed as point estimates and 95% confidence intervals. Results were compared using McNemar's test for paired samples.


RESULTS
ELISA sensitivity ranged from 70 to 98% and complement fixation test sensitivity from 60 to 96%; with POMP90-3 > POMP90-4 > CFT (parakeet) > CFT (turkey) > POMP80-90 > MOMP-P > CFT (sheep). There was no significant difference from POMP90-3 to POMP80-90 (P > 0.05). ELISA specificity ranged from 88 to 100% and CFT specificity was 100% for all three antigens; with CFT and POMP90-4 > MOMP-P > POMP80-90 > POMP90-3. There was no significant difference from CFT to POMP80-90 (P > 0.05). Changing the CFT cut-off from 1:32 to 1:4 substantially reduced the specificity with little improvement in sensitivity.


CONCLUSIONS
Assays using POMP90-4, POMP80-90, CFT (parakeet) and CFT (turkey) had equivalent sensitivity and specificity; none of the ELISAs were more specific than any CFT. The POMP80-90 ELISA is recommended as an alternative to CFT (parakeet) but as its specificity is not ideal the search for a more specific assay should continue.
McCauley
L M E
LM
Primary Industries Research Victoria, Department of Primary Industries, Attwood, VIC 3049, Australia. Lisette.McCauley@dpi.vic.gov.au
Lancaster
M J
MJ
Young
P
P
Butler
K L
KL
Ainsworth
C G V
CG
D000034:Abortion, Veterinary / Q000382:microbiology; D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood*; D000942:Antigens, Bacterial / Q000276:immunology; D023501:Chlamydophila / Q000276:immunology*; D023521:Chlamydophila Infections / Q000175:diagnosis / Q000453:epidemiology*; D003168:Complement Fixation Tests / Q000379:methods / Q000662:veterinary*; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000662:veterinary*; D005260:Female; D008297:Male; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000175:diagnosis / Q000453:epidemiology; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016036:Seroepidemiologic Studies; D012756:Sheep
D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial