Infection rates in reactors to an absorbed ELISA used in a test and cull program for bovine Johne's disease

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Section: Discussionmentioning

confidence: 85%

Section: Methodsmentioning

confidence: 99%

Estimate of the sensitivity of an ELISA used to detect Johne's disease in Victorian dairy cattle herds

Jubb¹,

Sergeant

Callinan³

et al. 2004

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“…By contrast, two studies over 10 years have demonstrated the high predictive value of positive ELISA results in known infected herds (S Ridge, MVSc Thesis, University of Melbourne 1994). 12 This study assessed management practices in known infected herds and sought to determine those factors that are important for the occurrence of new cases of BJD. The choice of the outcome being "ELISA positive animals or clinical cases born after the second whole herd test" is a very rigorous measure of the calf rearing practices undertaken in the herds since the start of the testing program.…”

Section: Management Variablementioning

confidence: 99%

Effect of compliance with recommended calf‐rearing practices on control of bovine Johne's disease

Se¹,

Im²,

Hannah

2005

Fifty-four south Gippsland dairy herds participating in the Victorian bovine Johne's disease test and control program were visited between July and November 2002 and an audit of calf rearing practices was conducted. The results of testing completed under the program were analysed for each of the herds. Twenty seven management factors were examined for a relationship with the presence of clinical cases of Johne's disease or cattle with positive ELISA test results that were born after the completion of the second whole herd test. Logistic regression was used to examine the strength of relationships between the management practices and the frequency with which new cases of Johne's disease arose. RESULTS AND CONCULSIONS: Calves were removed from their dams within 12 hours of birth in only 17 (31.5%) of the herds. However, in all but one herd the calves were removed within 24 hours of birth. In 42 herds (77.8%) calf rearing facilities were adequately separated from adult cattle and the faeces from adult cattle. In 41 herds (75.9%) calves up to the age of 12 months were grazed on paddocks that were free of manure or effluent from adult cattle. However, in only 10 (18.5%) of the herds were all three of these calf management practices applied. Feeding whole milk containing antibiotic residues, or providing water for calves from birth, were found to have statistically significant associations with an increased occurrence of cases of bovine Johne's disease in the study herds. The practice of allowing cows to calve in a paddock was found to be associated with reduced occurrence of bovine Johne's disease. These associations were still found after analysis that included herd size, the number of clinical cases that had occurred in the herds before the start of testing, the number of animals with positive ELISA tests that were detected at the first test and the number of years of participation in the test and cull program. Early separation of newborn calves from cows and grazing calves under 12 months of age in areas free of adult cattle were not found to be protective against Johne's disease.

“…This assumed that most reactors were infected 6 and that they were ical cases when reactors were removed, probably meant that testing removed animals for which clinical disease was imminent. This assumed that most reactors were infected 6 and that they were ical cases when reactors were removed, probably meant that testing removed animals for which clinical disease was imminent.…”

Section: Scientificscientificscientificscientificmentioning

confidence: 99%

“…The sensitivity of the ELISA (ability of the test to detect infected animals) at T1 appeared to be low because of the large number of animals that were tested negative at T1 but which were positive at later tests. This assumed that most reactors were infected 6 and that they were ical cases when reactors were removed, probably meant that testing removed animals for which clinical disease was imminent.…”

Section: Scientificscientificscientificscientificmentioning

confidence: 99%

Effect of a test and control program for bovine Johne's disease in Victorian dairy herds 1992 ‐ 2002

2004

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The TCP caused a marked decline in the number of clinical cases, probably because animals in which clinical disease was imminent were detected by testing and removed. A reduction in prevalence of reactors occurred only when most herd members were born after the TCP started. The sensitivity of the ELISA appears to be low based on the large number of reactors that were negative at T1 but were positive at later tests. Low sensitivity of diagnostic tests and the long incubation period of the disease limits meaningful analysis of the program until it has continued for some years. Measures adopted in the TCP have not broken the cycle of infection in many participating herds. It is unsure if this was because of poor compliance with control recommendations or a poor understanding of methods of transmission by scientists. Eradication is not feasible in the short-term.