Jubb T F, Galvin J W
Department of Primary Industries, Animal Health Operations Branch, Box 2500, Bendigo Delivery Centre, Victoria 3554.
Aust Vet J. 2004 Apr;82(4):228-32. doi: 10.1111/j.1751-0813.2004.tb12685.x.
To report on progress in Johne's disease (JD) control in infected dairy herds participating in the Victorian Johne's disease Test and Control Program (TCP).
Clinical histories and JD testing data recorded by the Department of Natural Resources and Environment (now called Department of Primary Industries) were analysed for 542 dairy herds participating in the TCP. The herds were required to conduct annual herd tests of cattle 2 years old and older with an enzyme linked immunosorbent assay (ELISA), cull the reactors and manage the younger cattle to minimise infection.
Testing of over 680,000 animals identified over 10,000 reactors giving an average prevalence of reactors at the first whole-herd test (T1) of 1.78%. There was a relatively rapid increase in the incidence of clinical disease before the TCP started and then it markedly declined. There was a slow and interrupted decline in reactor prevalence, with a marked peak occurring at the fourth herd test (T4). The average age of reactors and clinical cases was 5.7 and 5.9 years, respectively. Of the reactors and clinical cases detected during the TCP, 87% and 95% respectively, were born before the TCP started. Thirty herds completed the program by achieving three successive negative whole herd tests and 91 herds dropped out because of inability to comply with the agreed requirements of the program. There were no home-bred reactors born after the start of the program in 253 (47%) herds and of the 522 herds that were tested more than once, there were 319 (61%) herds in which no home-bred reactors were detected after the first year of testing. The number of ELISA positive animals detected at T1 appeared to be only about 26% of the animals from that round that subsequently became positive or developed clinical disease at later test rounds.
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.
报告参与维多利亚州约翰氏病检测与控制计划（TCP）的受感染奶牛场在约翰氏病（JD）控制方面的进展情况。
对参与TCP的542个奶牛场，分析自然资源与环境部（现称为初级产业部）记录的临床病史和JD检测数据。这些牛场被要求对2岁及以上的奶牛每年进行酶联免疫吸附测定（ELISA）群体检测，淘汰检测呈阳性的牛，并对年幼的牛进行管理以尽量减少感染。
对超过680,000头动物的检测发现了超过10,000头检测呈阳性的牛，在首次全群检测（T1）时，检测呈阳性的牛的平均患病率为1.78%。在TCP开始之前，临床疾病的发病率相对快速上升，之后则显著下降。检测呈阳性的牛的患病率呈缓慢且间断性下降，在第四次群体检测（T4）时出现明显峰值。检测呈阳性的牛和临床病例的平均年龄分别为5.7岁和5.9岁。在TCP期间检测出的检测呈阳性的牛和临床病例中，分别有87%和95%在TCP开始之前出生。30个牛场通过连续三次全群检测呈阴性完成了该计划，91个牛场因无法遵守该计划的商定要求而退出。在253个（47%）牛场中，没有在该计划开始后出生的自繁检测呈阳性的牛，在接受多次检测的522个牛场中，有319个（61%）牛场在检测的第一年之后未检测出自繁检测呈阳性的牛。在T1检测出的ELISA阳性动物数量似乎仅约为该轮中随后在后续检测轮次中呈阳性或出现临床疾病的动物数量的26%。
TCP使临床病例数量显著下降，可能是因为通过检测发现并移除了即将出现临床疾病的动物。只有当大多数牛群成员在TCP开始之后出生时，检测呈阳性的牛的患病率才会下降。基于大量在T1时呈阴性但在后续检测中呈阳性的检测呈阳性的牛，ELISA的敏感性似乎较低。诊断检测的低敏感性和该疾病的长潜伏期限制了对该计划进行有意义的分析，直到该计划持续数年。TCP中采取的措施并未在许多参与的牛场中打破感染循环。不确定这是因为对控制建议的遵守不佳还是科学家对传播方式的理解不足。短期内根除是不可行的。
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