Pathology and pathogenesis of bovine skin and meibomian gland demodicosis

Abstract

A national survey on bovine demodicosis was conducted among 48,000 cattle in Sudan during vaccination campaigns (44,800), and at antemortem and postmortem examination in abattoirs (3200). Among the total surveyed, 44,908 were adult (2-8 years) of which 34.6% were infected, and 3092 were calves (<  2 years) of which 34.6% were infected. Three hundred cattle with severe skin lesions among which 218 also had meibomian gland lesions were selected. The clinical pictures of skin and meibomian gland demodicosis were described. Proteus vulgaris, Pseudomonas aeruginosa, Staphylococcus aureus, Sta. epidermidis, Streptococcus pyogenes (group A) and Trueperella pyogenes were isolated from skin lesions, and Moraxella bovis and Sta. aureus were isolated from meibomian gland lesions. These bacteria produced deleterious toxins and enzymes aggravating the lesions caused by Demodex bovis and D. ghanensis mites in skin and meibomian glands, respectively. Neither mite was found in the internal tissues or organs, indicating that they had no endoparasitic phase. The histopathological changes observed were commensurate with cell-mediated immunity. Liberation of the contents of demodectic mange colonies in the subepidermal and dermal layers of the skin, and surrounding connective tissue of the meibomian glands evoked severe histopathological changes characterized by massive high-turnover granulomatous reactions with influx of macrophages and lymphocytes. The pathogenesis of the disease, from the stage of initial invasion of the hair follicles and collecting tubules of the meibomian glands by the mites and associated bacteria, to the stage of regression of the lesions was described. It was concluded that the nature of association between Demodex mites and bacteria in demodectic mange lesions was synergistic and of equal significance. The high-turnover granulomatous reactions which characterized the histopathological changes showed that Demodex mites and associated bacteria were persistent and immunogenic.