Discussion
Poultry red mites (prm) are small and highly mobile blood feeding ectoparasites that live off-host, only seeking a bird to rapidly engorge every few days. Prm are therefore difficult to contain in a controlled experimental environment that allows natural feeding on the host and in vitro feeding techniques have been previously employed to overcome containment issues (e.g. Mcdevitt et al., 2006). The in vitro feeding technique for the preliminary screening of prm vaccine candidates in small scale trials was refined by Bartley et al., 2015 but has several drawbacks, including a high background mite mortality and a high variability in feeding rates, requiring a technical and experimental replication to overcome this and it requires invasive blood sampling of hens. In addition, previous studies have shown that vaccine efficacy measured using the in vitro feeding device is not always translated into mite population reduction in field trials (Bartley et al., 2017) leading to false indications of the potential of a vaccine. A prototype ‘on-hen’ in vivo mite feeding device for adult mites was therefore developed as an alternative to the in vitro assays for more accurate pre-screening of potential novel interventions before embarking on field studies. This is an important development in reduction and refinement of animals and in keeping with 3r’s approaches. The device consisted of a sealed 250μm aperture mesh pouch containing pre-starved, adult mites. They were applied to the (plucked) skin of the hen’s thigh and secured with medical tape and elasticated bandage. Fed adult mites were recovered from the device, enumerated and maintained to monitor mortality and fecundity. This on-hen device resulted in a consistent feeding rate of 50% of adult mites following a 3h feeding period and only a low background mite mortality was observed. Here we describe the optimisation of the feeding device for protonymph, deutonymph and adult life stages. Preliminary studies evaluated three nylon meshes (75μm, 120μm, 125 μm aperture), three polyester meshes (68 μm, 105 μm and 120 μm aperture) and two device designs. The best device and two mesh sizes (105 μm and 120 μm) were further adjusted and evaluated for feeding and survival rates among the three life stages, hen welfare and comfort, mite recovery from the devices.the 105μm provided the best interface for each life stage resulting in a mean feeding rate up to 10% for protonymphs, 26% for deutonymphs and 59% for adults with both aperture size and mesh thickness affecting feeding of the juvenile life stages. The most successful design was employed in a mite conditioning study to maximise feeding rates with an optimised regime of one week at room temperature (rt) and two weeks at 4oc for both adults and protonymphs and one week at room temperature (rt) and one week at 4oc for deutonymphs. This device represents a high hen-welfare method of allowing mites to feed on the live host whilst maintaining prm containment and has great potential as a tool to allow feeding of nymph and adult life stages to evaluate systemic prm controls (e.g. Vaccines, systemic acaricides).
References: Bartley K., Wright HW., Huntley JF., Manson ED., Inglis NF., Mclean K., Nath M., Bartley Y., Nisbet AJ. 2015. Identification and evaluation of vaccine candidate antigens from the poultry red mite (Dermanyssus gallinae). Int j parasitol. 45:819-30. Bartley K., Turnbull F, Wright HW., Huntley JF., Palarea-Albaladejo J., Nath M., Nisbet AJ. 2017. Field evaluation of poultry red mite (Dermanyssus gallinae) native and recombinant prototype vaccines. Vet parasitol. 244: 25-34. Mcdevitt R., Nisbet AJ., Huntley JF. 2006. Ability of a proteinase inhibitor mixture to kill poultry red mite, dermanyssus gallinae in an in vitro feeding system.
