A technique to test novel methods of controlling poultry red mite in hens without performing field-scale trials

无论采用哪种产蛋系统，鸡舍中的家禽红螨（PRM）的侵扰都是世界范围内蛋品行业的主要动物福利和经济问题。PRM对产蛋鸡的两个主要影响是螨叮咬鸟类并吸食其血液导致刺激和贫血的直接影响，以及螨将疾病传播给母鸡造成的间接影响。传统的方法控制PRM与化学喷雾在鸡舍现在失败的螨成为耐药的化学品。因此，对控制PRM的新方法的需求很高，世界各地的几个研究小组正在研究这些新的控制方法。通常情况下，新的控制方法的测试使用螨在实验室为基础的测试最初，然后是现场测试使用大量的母鸡。例如，控制PRM的疫苗开发通常使用初始实验室筛选测试来识别潜在的疫苗，然后再进入田间试验，每次试验可使用多达800只母鸡，持续数月。这种策略有两个主要的缺点：1）基于实验室的分析结果是高度可变的，可能无法准确预测田间试验中发生的情况; 2）田间试验涉及大量鸟类长时间持续暴露于寄生虫。为了解决这些问题，我们开发了一种“母鸡上”螨喂养装置，作为实验室测试的替代方案，这将允许在进行田间研究之前对少量母鸡的疫苗和其他螨控制方法进行更准确的评估。该策略通过大幅减少所用母鸡的数量来解决3Rs原则的“减少”方面，因为它将在进行田间试验之前准确地识别性能差的疫苗或其他控制方法（例如新农药）。这种母鸡上系统也可用于测试螨控制方法在小数量母鸡（每个处理组4只，而田间试验中每个处理组400只）上的长期有效性，而不会使鸟类持续暴露于寄生虫。因此，这解决了第二个3Rs原则-“细化”，因为它允许鸟类在实验期间的绝大多数时间内保持无寄生虫，寄生虫每3周仅在短时间（3小时）内接触鸟类，而不是在田间试验中遇到的持续暴露。在PRM的田间侵染期间，螨的3个发育阶段中的每一个都以宿主为食; 2个幼年阶段和成年阶段。到目前为止，我们设计的母鸡上装置允许成螨以母鸡为食，但任何疫苗或新型杀螨剂都应对螨的三个吸血阶段中的每一个产生影响，以获得最大功效，并且任何使用母鸡上喂食装置作为感染模型代表的测试策略都应能够确定这些影响。因此，拟议工作的具体目的是进一步将母鸡饲养装置开发成一种高度可靠的工具，用于监测新型螨控制方法对寄生虫存活和传播疾病能力的有效性，从而减少对大规模长期田间试验的依赖。这一目标将通过一系列实验来实现，如下：1）优化装置的设计，以允许寄生虫的所有阶段进食。2)确定母鸡年龄对使用饲喂装置能力的影响3）在扩展疫苗效力研究中使用优化的饲喂装置4）在疾病传播研究中使用优化的饲喂装置

Infestation of hen houses with poultry red mites (PRM) is a major animal welfare and economic problem for the egg industry worldwide, irrespective of the type of laying systems employed. The two main impacts of PRM on laying hens are direct effects of the mites biting the birds and feeding on their blood which causes irritation and anaemia, and indirect effects caused by the mites transmitting diseases to the hens. Traditional methods of controlling PRM with chemical sprays in hen houses are now failing as the mites become resistant to the chemicals. Demand for novel methods of controlling PRM is therefore high and several research groups around the world are working on these new methods of control. Typically, the testing of novel control methods uses mites in laboratory-based tests initially, followed by field testing using large numbers of hens. For example, the development of vaccines to control PRM routinely uses initial laboratory-screening tests to identify potential vaccines before moving into field trials which can use up to 800 hens in each trial and last for several months. This strategy has 2 major drawbacks:1) Results from the laboratory-based analyses are highly variable and may not accurately predict what happens in field trials;2) Field trials involve large numbers of birds continually exposed to parasites for prolonged periods.To address these issues we have developed an 'on-hen' mite feeding device, as an alternative to the laboratory-based tests, which will allow much more accurate assessment of vaccines and other mite control methods on small numbers of hens before field studies are conducted. This strategy addresses the "Reduction" aspect of the 3Rs principles by greatly reducing the number of hens used, as it would accurately identify poorly performing vaccines or other control methods (e.g. new pesticides) before they were progressed to field trials. This on-hen system can also be used to test the effectiveness of mite control methods across prolonged periods on small numbers of hens (4 per treatment group, as opposed to 400 per treatment group in field trials) without continually exposing birds to the parasites. This therefore addresses a second 3Rs principle - "Refinement" as it allows the birds to remain free from the parasites for the vast majority of the experimental period, with parasites only accessing the birds for short (3 hour) periods every 3 weeks instead of the continual exposure encountered in field trials. During a field infestation of PRM each of 3 developmental stages of the mites feeds on the host; 2 juvenile stages and the adult stage. So far we have designed the on-hen device to allow adult mites to feed on the hen but any vaccine or novel acaricide should have effects on each of the three blood-feeding stages of the mite for maximum efficacy and any testing strategy which uses an on-hen feeding device as a proxy for infestation models should be able to determine these effects. The specific aim of the proposed work is therefore to further develop the on-hen feeding device into a highly reliable tool for monitoring the effectiveness of novel mite control methods on parasite survival and ability to transmit disease and therefore reduce the reliance on large scale, prolonged field trials. This aim will be achieved through a series of experiments, as follows:1) Optimise design of the device to allow feeding by all stages of the parasite. 2) Determine effects of hen age on the ability to use the feeding devices3) Employ the optimised feeding devices in an extended vaccine efficacy study4) Employ the optimised feeding devices in a disease transmission study