Evaluation of vaccine delivery systems for inducing long-lived antibody responses to <i>Dermanyssus gallinae</i> antigen in laying hens

<i>Dermanyssus gallinae</i>, the poultry red mite, is a global threat to the commercial egg-laying industry. Control of <i>D. gallinae</i> is difficult, with only a limited number of effective pesticides and non-chemical treatments available. Here, we characterize the candidate vaccine antigen <i>D. gallinae</i> cathepsin D-1 (Dg-CatD-1) and demonstrate that purified refolded recombinant Dg-Cat-D1 (rDg-CatD-1) is an active aspartyl proteinase which digests haemoglobin with a pH optimum of pH 4. Soluble protein extracts from <i>D. gallinae</i> also have haemoglobinase activity, with a pH optimum comparable to the recombinant protein, and both proteinase activities were inhibited by the aspartyl proteinase inhibitor Pepstatin A. Enzyme activity and the ubiquitous localization of Dg-CatD-1 protein in sections of adult female mites is consistent with Dg-CatD-1 being a lysosomal proteinase. Using Dg-CatD-1 as a model vaccine antigen, we compared vaccine delivery methods in laying hens via vaccination with: (i) purified rDg-CatD-1 with Montanide™ ISA 71 VG adjuvant; (ii) recombinant DNA vaccines for expression of rDg-CatD-1 and (iii) transgenic coccidial parasite <i>Eimeria tenella</i> expressing rDg-CatD-1. In two independent trials, only birds vaccinated with rDg-CatD-1 with Montanide™ ISA 71 VG produced a strong and long-lasting serum anti-rDg-Cat-D1 IgY response, which was significantly higher than that in control birds vaccinated with adjuvant only. Furthermore, we showed that egg-laying rates of <i>D. gallinae</i> mites fed on birds vaccinated with rDg-CatD-1 in Montanide™ ISA 71 VG was reduced significantly compared with mites fed on unvaccinated birds. <b>RESEARCH HIGHLIGHTS</b><i>Dermanyssus gallinae</i> cathepsin D-1 (Dg-CatD-1) digests haemoglobinVaccination of hens with rDg-CatD-1 in Montanide™ ISA 71 VG results in long-lasting IgY levelsSerum anti-rDg-CatD-1 antibodies reduce egg laying in <i>D. gallinae</i> after a single blood meal <i>Dermanyssus gallinae</i> cathepsin D-1 (Dg-CatD-1) digests haemoglobin Vaccination of hens with rDg-CatD-1 in Montanide™ ISA 71 VG results in long-lasting IgY levels Serum anti-rDg-CatD-1 antibodies reduce egg laying in <i>D. gallinae</i> after a single blood meal