Poultry red mites (Dermanyssus gallinae) are blood-feeding ectoparasites that infest the accommodation of birds. Infestation of hen houses has implications both for hen welfare and the economics of the egg-producing industry worldwide. Poultry red mites biting and feeding on hens causes irritation and anaemia, leading to losses in production. Demand for new and novel methods of controlling poultry red mites is high as current treatment options are limited and resistance is developing to chemical treatments. The testing of novel control methods initially uses mites in in vitro laboratory-based tests to test efficacy followed by field testing, which requires large numbers of hens to be continually exposed to poultry red mites for prolonged periods.
Why we funded it
This Project Grant aims to reduce the number of hens used in field trials by optimising an “on-hen mite feeding device” for accurate assessment of the efficacy of vaccines and other mite control methods prior to field-scale trials.
In the last ten years, 47 research papers were published assessing novel interventions for poultry red mite control, compared to 17 published in the 40 years prior to 2007. The two main areas of growth were the development of vaccines and novel acaricides/novel uses for existing acaricides. Field trials for novel acaricides can employ up to 300 hens and development of vaccines against poultry red mites can require up to 800 hens. The on-hen mite feeding device will be used to pre-screen vaccine formulations for efficacy in Dr Nisbet’s group prior to performing field trials. Pre-screening using the device requires approximately four hens per treatment group, compared to 400 per treatment group required in field trials. Field trials also require continual exposure of the hens to the parasites, however using the device poultry red mites will only be able to access birds for short periods in a controlled manner.
The on-hen feeding device consists of a sealed mesh device containing pre-starved mites. The device is secured to the skin of a hen’s thigh and fed mites are recovered from the device for monitoring. In a field infestation of poultry red mites, each of three developmental stages feeds on the hen so for maximal efficacy any vaccine or acaricide needs to impact on each of these stages. Initial work aims to optimise the design of the device to allow feeding by all developmental stages of the parasites by altering the pore size of the mesh. Mites will be allowed to feed for three hours before the devices are removed, the fed mites isolated and then monitored for mortality and fecundity. The impact of the aging of hens on the ability of the mites to feed using the optimised devices will also be determined. Field trials typically start with hens when they start to lay eggs at approximately 18 weeks old and run for up to 20 to 30 weeks to ensure efficacy persists throughout. It is possible that during this period, the skin of a chicken alters, either chemically or physically or both, and this may impact on the ability of the mites to feed using the on-hen device. After optimisation, the devices will be used in a longitudinal vaccine efficacy study to measure the impact of vaccination on the survival of mites at all developmental stages.