A molecular epidemiological approach to combating footrot an endemic disease of sheep

羊跛是痛苦的。在英国，超过95%的羊群在任何时候都有大约10%的羊跛行，其中80%的跛行是由步行引起的。在任何时候，英国大约有160万只跛羊。据估计，Footrot每年给英国产业造成3100万英镑的损失，这对羊农来说是一个巨大的担忧，他们认为控制这种疾病的建议并不成功。足癣是一种传染性疾病，由一种叫做结节双杆菌的细菌侵入足爪之间的皮肤引起。令人惊讶的是，对于这种细菌是如何引起疾病的，以及它在不引起疾病的情况下（在羊身上或在环境中）是如何存活的，人们知之甚少。在过去的7年里，我们研究了控制小跑的实际方面。关键结果是，及时用注射抗生素治疗跛羊的农民，其羊群中跛羊的发病率较低（4%对12%），而且修剪脚（传统上用于控制脚跑）与高发病率有关。这些事实表明，这种细菌在环境中的传播范围可能比之前在澳大利亚的研究中所怀疑的要广泛得多。我们知道环境在疾病的发生中起着重要作用。结藻在温暖潮湿的天气中生存得更好。我们还知道，有几种细菌菌株可以影响疾病的严重程度。然而，我们不知道环境或细菌菌株的哪些方面在决定农场疾病的严重性和持久性方面是重要的。这种细菌可以在牧场、肠道或未患病羊的脚上存活。在我们的工作中，我们从患病和未患病的羊的拭子中收集了大量的结节棘球蚴，并从羊脚中储存了细菌DNA。我们也有大约800只母羊和它们的羊羔两年的数据。每一次跛行都被记录和调查，并采取样本调查是否存在结节病。根据这些数据，我们可以建立数学模型，描述一只羊何时跛了腿，跛了多久，以及影响它恢复速度的因素，对一些羊来说，不幸的是，它又跛了。我们提出的工作计划是对上述数据进行分析，并在实验室研究中增加关于结节芽孢杆菌菌株致病能力及其在环境中的生存能力的新发现。利用这些研究的结果和我们的模型，我们将能够计算出哪一种结节梭菌引起了大多数疾病，以及环境和宿主对它们的生存有多重要。最终目的是为控制小跑提供更好的建议，从而降低这种疾病的发生。

Lameness in sheep is painful. In Great Britain over 95% of flocks have approximately 10% of sheep lame at any one time and 80% of this lameness is caused by footrot. There are approximately 1.6 million lame sheep in GB at any time. Footrot is estimated to cost the UK industry £31 million per year and is a huge worry to sheep farmers who do not feel that advice to manage this disease is successful. Footrot is an infectious disease caused by invasion of the skin between the claws of the foot with a bacterium called Dichelobacter nodosus. Surprisingly little is known about how this bacterium causes disease and how it survives (on the sheep or in the environment) when it is not causing disease. Over the past 7 years we have studied practical aspects of control of footrot. The key results were that farmers who treated lame sheep promptly with injectable antibiotics had low levels of lame sheep in their flocks (4% versus 12%) and also that trimming feet (traditionally used to control footrot) was associated with high levels of disease. These facts suggest that the bacteria may be much more widely spread in the environment than previously suspected from research in Australia. We know that the environment plays a role in disease occurrence. D. nodosus survives better in warm wet weather. We also know that there are several strains of the bacterium that can affect the severity of disease. However, we do not know which aspects of the environment or the bacterial strains are important in determining disease severity and persistence on farms. The bacteria may survive in pasture, in the gut or on feet of the non-diseased sheep. During our work we collected a large store of D. nodosus from swabs of sheep with and without disease and also stored bacterial DNA from the feet of sheep. We also have two years data from approximately 800 ewes and their lambs. Every occurrence of lameness has been recorded and investigated and samples taken to investigate whether D. nodosus was present. From these data we can form mathematical models that describe when a sheep became lame, how long she was lame for and factors that influenced the speed with which she recovered and, unfortunately for some, became lame again. The plan of work we propose is to analyse the data above as described and to add in new findings about D. nodosus from laboratory studies into the ability of strains to cause disease and their survival in the environment. Using results from these studies and our models we will be able to work out which strains of D. nodosus cause most disease and how important the environment and host are in their survival. The ultimate aim is to provide better advice on control of footrot and so lower the occurrence of this disease.