Estimate of the sensitivity of an ELISA used to detect Johne's disease in Victorian dairy cattle herds.
OBJECTIVE
To estimate the sensitivity of the ELISA used in dairy cattle herds participating in the Victorian Bovine Johne's Disease Test and Control Program (TCP).


METHODS
The percentage of ELISA reactors in age and test cohorts was estimated from age-specific test data derived from TCP herds with long testing histories. Age-distribution data from production-tested herds enabled estimation of reactor rates in animals that were culled or died.


RESULTS
ELISA sensitivities at the first test round in herds achieving five, six and seven annual herd tests were 16.1, 14.9 and 13.5% respectively. The ELISA sensitivity in 2, 3 and 4-year-old animals at the first test round in herds testing seven times was 1.2, 8.9 and 11.6% respectively but remained between 20 and 30% in older age-groups.


CONCLUSIONS
The sensitivity of the ELISA is considerably lower than previous estimates, probably because previous estimates were predominantly measured against faecal culture, which has subsequently been shown to have low sensitivity itself, and did not appreciate the long period that appears to precede detectable faecal excretion in most animals.
Department of Primary Industries, Box 2500, Bendigo Delivery Centre, Victoria 3554.
T F
TF
Jubb
E S G
ES
Sergeant
A P L
AP
Callinan
J
J
Galvin
D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000175:diagnosis* / Q000453:epidemiology* / Q000209:etiology / Q000517:prevention & control; D003612:Dairying; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000662:veterinary*; D005260:Female; D016927:Mycobacterium avium subsp. paratuberculosis / Q000276:immunology / Q000302:isolation & purification; D010283:Paratuberculosis / Q000175:diagnosis* / Q000453:epidemiology* / Q000209:etiology / Q000517:prevention & control; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D014739:Victoria / Q000453:epidemiology