Haematological and immunological response of unrestrained cattle to Psoroptes ovis, the sheep scab mite.

Cows were infected twice with 600 and 500 nymphs and adults of a bovine strain of Psoroptes ovis with a nine-week interval. The haematological response and the non-specific mitogen- and antigen-induced responsiveness of the peripheral blood lymphocytes of the animals was followed. Dermal reactivity to P ovis antigen injection was studied five weeks after reinfection. After the first infection with 600 mites none of the infected animals developed clinical psoroptic mange but a leucocytosis developed, contributed to primarily by an eosinophilia and by a slight lymphocytosis. Antigen-induced lymphocyte blastogenesis was used to measure the antigen-sensitive cell population in peripheral blood and this population showed a maximum increase 10 days after infection; however, antigen-sensitive cells remained above normal levels until reinfection. Upon challenge infection with 500 mites the infected animals showed an immediate hypersensitivity type reaction with a marked pruritus, scratching and exudation. Thereafter the lesions healed rapidly and none of the animals developed clinical mange. This clinical reaction was accompanied by a secondary eosinophilia but no change was apparent in the other blood elements. A marked increase in the blastogenic response of the peripheral blood lymphocytes was also apparent and this peaked three weeks after challenge. Following the intradermal injection of P ovis antigen there was an immediate swelling of the injection site in all infected and control animals and skin thickness was maximal one hour after injection. Thereafter there was a clear distinction in dermal reactions between P ovis infected and control animals; after 48 hours reactions were not seen in the control animals while marked dermal reactions were still present in the P ovis infected group.