MYCOPLASMA BOVIS ASSOCIATED DISEASES: MODELING STRESS AND ITS EFFECT ON BOVINE IMMUNE FUNCTION
Alabdullah, Hussain Ali
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Mycoplasma bovis associated diseases are newly emerging causing significant economic losses in the cattle industry. Therefore, it is necessary to understand the pathogenesis of M. bovis to develop new preventive methods to this group of diseases. The major research focus reported herein was to better understand the interactive impairment of the cattle’s immune system by stress and M. bovis and subsequent increase in Mycoplasma bovis associated diseases. The first specific objective was to develop a stress model to study impairment of the bovine immune system as reflected by M. bovis shedding in colonized calves. Two experimental trials to mimic the effect of stress through synthetic glucocorticoid administration (dexamethasone) on M. bovis shedding were conducted. Results of both trials showed that the onset, the duration, and the likelihood of calves shedding M. bovis, were significantly greater in dexamethasone treated calves compared to controls. Through the second and third objectives, we evaluated neutrophil functions as affected by dexamethasone and four opsonized M. bovis strains or dexamethasone and four unopsonized M. bovis strains respectively. Dexamethasone consistently decreased all neutrophil functions tested with opsonized or unopsonized M. bovis. There were strain and strain by treatment interaction effects on some neutrophil functions. This interaction had an additive effect on neutrophil killing. The interaction of M. bovis and dexamethasone on bovine neutrophil killing might explain in part the association of stressful events with subsequent outbreaks of Mycoplasma bovis associated diseases. The stress model may aid in further study of the interaction between M. bovis and stress for evaluating new control measures for M. bovis infection in cattle.