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

鸡舍感染家禽红螨（PRM）是世界范围内蛋业的一个主要动物福利和经济问题，无论采用哪种类型的产蛋系统。PRM对蛋鸡的影响主要有两方面：一是螨虫叮咬蛋鸡，取食蛋鸡血液导致蛋鸡过敏和贫血；二是螨虫传播疾病给蛋鸡造成间接影响。传统的在鸡舍里喷洒化学药剂来控制PRM的方法现在已经失效了，因为这些螨虫已经对化学药剂产生了抗药性。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，对新型控制方法的测试首先在实验室测试中使用螨虫，然后使用大量母鸡进行现场测试。例如，控制PRM的疫苗的开发通常使用最初的实验室筛选试验来确定潜在的疫苗，然后再进入实地试验，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，可能无法准确预测现场试验的结果；野外试验涉及大量鸟类长期暴露于寄生虫。为了解决这些问题，我们开发了一种“母鸡身上”的螨虫喂养装置，作为实验室测试的替代方法，它将允许在进行实地研究之前更准确地评估疫苗和其他螨虫控制方法。该战略通过大大减少母鸡的使用数量，解决了3r原则的“减少”方面的问题，因为它将在疫苗或其他控制方法（例如新农药）进入田间试验之前准确地识别出效果不佳的疫苗或其他控制方法。这种对母鸡的系统也可用于在不持续将鸟类暴露于寄生虫的情况下，对少量母鸡（每个处理组4只，而不是现场试验中每个处理组400只）长期测试螨虫控制方法的有效性。因此，这解决了第二个3Rs原则-“细化”，因为它允许鸟类在绝大多数实验期间保持远离寄生虫，寄生虫每三周只在短时间内（3小时）接触鸟类，而不是在现场试验中遇到的持续暴露。在田间侵染PRM期间，3个发育阶段的螨均以寄主为食；2个幼年期和成虫期。到目前为止，我们已经设计了对母鸡的装置，允许成年螨以母鸡为食，但任何疫苗或新型杀螨剂都应该对螨虫的三个吸血阶段的每一个阶段都有影响，以获得最大的功效，任何使用对母鸡的喂养装置作为感染模型的代理的测试策略都应该能够确定这些影响。因此，拟议工作的具体目标是进一步发展母鸡饲养装置，使其成为一种高度可靠的工具，用于监测新型螨虫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、长时间田间试验的依赖。这一目标将通过以下一系列实验来实现：1)优化设备设计，使寄生虫能够在所有阶段进食。2)确定母鸡年龄对饲喂装置使用能力的影响3)在扩展的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