Angell J W, Grove-White D H, Duncan J S
Department of Epidemiology and Population Health, Institute of Infection and Global Health, The University of Liverpool, Leahurst Campus, Neston, Wirral, CH64 7TE, UK.
Department of Epidemiology and Population Health, Institute of Infection and Global Health, The University of Liverpool, Leahurst Campus, Neston, Wirral, CH64 7TE, UK.
Prev Vet Med. 2015 Nov 1;122(1-2):107-20. doi: 10.1016/j.prevetmed.2015.09.016. Epub 2015 Oct 13.
Contagious ovine digital dermatitis (CODD) is a cause of severe lameness in sheep in the UK currently affecting approximately 50% of farms. Six farms were studied in North Wales to investigate (1) the prevalence dynamics of CODD, (2) the association between sheep with CODD and potential risk factors and (3) the impact of CODD on lameness in sheep. The farms were visited at approximately two-month intervals between June 2012 and October 2013 and 6515 sheep were examined. The mean sheep level prevalence of CODD varied between farms (2.5-11.9%). Within farms, prevalence may increase in the late summer/early autumn and after housing. Environmental risk factors included larger flocks, lowland pasture, lush pasture and poached pasture. Co-infection of a foot with footrot was strongly associated with CODD in that foot (OR: 7.7 95% CI: 3.9-15.5 P<0.001) but negatively associated with co-infection of a foot with interdigital dermatitis (OR: 0.04 95% CI: 0.02-0.1 P<0.001). Reinfection with CODD was observed in 78 individual sheep but there was no re-infection at foot level. Lameness on all farms reduced during the study and seasonal changes in lameness followed similar patterns to those for CODD. Infection with CODD leads to a greater increase in locomotion score compared to footrot or interdigital dermatitis and CODD lesion grade was strongly associated with being lame. Sheep with CODD in more than one foot were more likely to be lame (OR: 25.0 95% CI: 12.5-49.9 P<0.001) than those with just one foot affected (OR:10.0 95% CI: 8.6-11.6 P<0.001). The biggest risk factor for CODD is co-infection with footrot and therefore control of footrot should help reduce the risk of CODD on affected farms. Furthermore environmental risk factors for CODD are similar to those for footrot adding weight for control strategies that target both diseases in tandem. The routine repeated gathering of sheep for the purposes of treating all lame sheep might be an effective control strategy for lameness on some sheep farms. Effective systemic immunity to CODD in sheep appears to be lacking, as 78 sheep were observed to be re-infected with CODD during the survey. However, there is epidemiological evidence that there may be some local immunity within the foot warranting further investigation.
传染性绵羊蹄皮炎（CODD）是英国绵羊严重跛行的一个病因，目前约50%的农场受到影响。在北威尔士对六个农场进行了研究，以调查（1）CODD的流行动态，（2）患CODD的绵羊与潜在风险因素之间的关联，以及（3）CODD对绵羊跛行的影响。在2012年6月至2013年10月期间，大约每隔两个月对这些农场进行一次走访，共检查了6515只绵羊。各农场CODD的绵羊平均感染率有所不同（2.5 - 11.9%）。在农场内部，感染率可能在夏末/初秋以及入舍后有所上升。环境风险因素包括羊群规模较大、低地牧场、茂盛的牧场和被践踏的牧场。一只脚同时感染腐蹄病与该只脚感染CODD密切相关（比值比：7.7，95%置信区间：3.9 - 15.5，P<0.001），但与该只脚同时感染趾间皮炎呈负相关（比值比：0.04，95%置信区间：0.02 - 0.1，P<0.001）。观察到78只个体绵羊再次感染CODD，但在蹄部层面没有再次感染。在研究期间，所有农场的跛行情况都有所减轻，跛行的季节性变化与CODD的情况遵循相似模式。与腐蹄病或趾间皮炎相比，感染CODD导致运动评分的增加幅度更大，并且CODD病变等级与跛行密切相关。一只以上脚感染CODD的绵羊比仅一只脚受影响的绵羊更易跛行（比值比：25.0，95%置信区间：12.5 - 49.9，P<0.001）（仅一只脚受影响的绵羊比值比：10.0，95%置信区间：8.6 - 11.6，P<0.001）。CODD的最大风险因素是与腐蹄病共同感染，因此控制腐蹄病应有助于降低受影响农场中CODD的风险。此外，CODD的环境风险因素与腐蹄病相似，这为同时针对这两种疾病的控制策略提供了更多依据。为治疗所有跛行绵羊而定期反复聚集绵羊，可能是一些绵羊农场控制跛行的有效策略。绵羊似乎缺乏对CODD有效的全身免疫力，因为在调查期间观察到78只绵羊再次感染了CODD。然而，有流行病学证据表明蹄部可能存在一些局部免疫力，值得进一步研究。
