Scaling up For commercial operations, however, it would be necessary to identify the components that control red mite and produce them as synthetic proteins. “Then you would have a commer- cialisable vaccine.” The next stage took some three years. Work- ing out which components produced the antibody reaction in hens and synthetically reproducing them. “Unfortunately, the vaccine didn’t work. That’s often the case when you’re trying to develop a synthetic vaccine made from a native extract.” The research team “took a step back” to work out what was needed to create a vaccine. A well-annotated genome was one element necessary to help understand more about how the red mite works. “When we first sequenced the genome we were really surprised by how big it is.” Another surprise was how closely related it was to ticks. “This is really a mini tick that we’re dealing with. That gave us cause for optimism because the only other commercialised vaccine against an ectoparasite is against the tick.” Another tool was aimed at creating a way to reliably test vac- cines on a small scale without going into the field for more expensive large-scale trials. The result was a small ‘teabag’ that opens at one end so that mites can be added. The mesh is just large enough for them to put their heads through to bite birds but not big enough for them to escape. Once
attached to birds’ legs it gives an easy way to assess how ef- fective prototype vaccines are. “That’s been a real refinement of the process,” Dr Nisbet added.
Prototype The genome was used to understand which genes are switched on in mites after they feed. One protein breaks down haemoglobin, interrupting the mite’s ability to digest food. That was mixed with an adjuvant and tested using the teabag tester. Results from that protein found a high anti- body response. Mites that fed on inoculated birds’ blood pro- duced 50% fewer eggs. “So, we’ve now gone through a ra- tional process for identifying a vaccine, we now need to know if that is enough to suppress populations in the field. Do we have to add other antigens to make it better and actually kill mites, rather than just suppress populations?” While promis- ing, Dr Nisbet says that the idea is not to replace other treat- ments against red mite but to complement them as part of an integrated pest management system. “There’s been a huge amount of work done over a great many years and we’re now at a really exciting point in the project,” Dr Nisbet concluded.
*This article was based on a poultry and pig health and welfare session hosted by the Moredun Research Institute.
▶ POULTRY WORLD | No. 2, 2020 25
The cost of red mite across Eu- rope has been put at € 230 mil- lion in lost pro- duction every year.
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