Studies on the Immune Mechanisms and Immunopathology of Severe Skin and Meibomian Gland Demodicosis in Cattle

Abstract

Cattle infected with severe and generalized skin and simultaneous meibomian gland lesions of demodectic mange; had higher total serum proteins, significantly higher globulin and lower albumin concentration than non-infected ones. The protein content of the soluble antigen of Demodex mites and associated bacteria was 70 µg /100 µl. Hypersensitivity testing of infected cattle by the intradermal injection of soluble mite and bacterial antigens produced immediate, delayed cell-mediated and Arthus immune-complex reactions, while non-infected cattle were refractory to these tests. The enzyme-linked immunoelectrotrasfer blot gave positive reaction bands at 56 kilodaltons (KDD) when the resolved soluble antigen was probed with sera from infected cattle and no reaction bands were demonstrated in sera from non-infected animals. The nature of association between Demodex mites and bacteria in demodectic mange lesions was synergistic and of equal significance. Pathogenic and opportunistic bacteria facilitated the establishment of Demodex mites in the lesions produced and provided an excellent microclimate for the mites to propagate and reproduce, resulting in severe and progressive disease. Histopathological examination showed severe changes characterized by massive ‘high-turnover’ granulomatous reaction with influx of macrophages and lymphocytes proving that Demodex mites and associated bacteria were both persistent and immunogenic. Giant cells destroyed, engulfed and digested the bacteria and the mites, resulting in healing of the lesions as judged by the progressive proliferation of connective tissue and degeneration of the granulomas. In spite of the rapid and exaggerated humoral and cell-mediated immune responses demonstrated in vivo and in vitro, the mites and associated bacteria remained viable in chronic lesions for 2-3 years. Failure of these cattle to develop acquired immunity against repeated exposure to the mites and associated bacteria was probably due to the development of tolerance resulting from the release of large amounts of soluble and particulate antigens.