Assessment of the acaricidal potential of the plasma from chickens immunised with the recombinant cysteine protease protein from PRMs (Deg-CPR-1) against poultry red mites (PRMs, Dermanyssus gallinae). (A) The production of antibody in the plasma from chickens immunised with Deg-CPR-1. Four chickens were immunised with Deg-CPR-1 and three chickens were unimmunised. The plasma was isolated from immunised and unimmunised chickens, and the antibody specific to Deg-CPR-1 in the plasma was detected by western blotting. The arrow head indicates the predicted molecular weight of Deg-CPR-1 (63 kDa). (B and C) The mortality rate of PRMs that were fed blood containing the plasma from immunised chickens was assessed every day for 1 week. Four and three plasma samples isolated from the immunised or unimmunised chickens were used in the in vitro feeding assays, and the total number of blood-feeding PRMs monitored was as follows: immunised: n = 155; unimmunised: n = 89 (B). The total number of PRMs fed blood containing the plasma with high antibody titre or low antibody titre was as follows: high antibody titre: n = 74; low antibody titre: n = 81 (C). The number of dead PRMs was recorded and plotted on the graph to generate Kaplan–Meier curves. Statistical analysis was performed using a log-rank test. Results with p < 0.01 were considered statistically significant.