How the calf's innate immune response affects the development of Mycoplasma bovis pneumonia in beef cattle
The patterns of respiratory disease in beef cattle have changed in the past 15 years. Mycoplasma bovis has emerged as a major cause of pneumonia and arthritis in Ontario feedlot cattle, veal calves and young beef calves. The disease is important because of its frequency (54% of mortalities in Ontario feedlots), economic losses, and the producer frustration and animal welfare issues resulting from chronic pneumonia and arthritis that often responds poorly to therapy. Current vaccines are not effective, and control is based on mass-medication with antibiotics. Most feedlot calves become infected but few develop disease. Lack of progress in more effectively controlling the disease reflects lack of knowledge about how the disease develops, and why only a few infected calves develop disease. Our prior studies (see "Related Research" below) suggest that:
(a) Mycoplasma bovis colonizes the lesions caused by other bacteria, leading to chronic lung damage and pneumonia that is resistant to antibiotics. We suspect that it is the inflammation and/or the lung damage caused by this initial bout of pneumonia, that creates an environment in the lung that promotes growth of Mycoplasma bovis.
(b) Mycoplasma bovis infection doesn’t directly damage lung tissue, but instead directs the calf’s inflammatory response to degrade lipids and proteins important for lung function.
Better understanding of how this disease develops is important for improved methods to prevent and treat the disease.
The specific research objectives are:
1. Determine how Mycoplasma bovis causes damage to the lung.
2. Determine how diseased lung tissue affects the immune response to Mycoplasma bovis infection, and leads to either a protective immune response or to a harmful inflammatory response causing lung damage and disease.
The findings of these studies are expected to be of direct benefit by leading to methods for improved control of this recently emerged and economically important disease. For example, the outcomes of these studies will indicate whether control methods for Mycoplasma bovis pneumonia should emphasize (a) prevention of the initial Mannheimia haemolytica pneumonia such as by preconditioning and metaphylaxis, (b) modifying the inflammatory response and type of innate immune response in the lung such as with already-licensed anti-inflammatory drugs, (c) preventing virus-induced necrosis of lung tissue by vaccination, or (d) minimizing lung necrosis through testing of antioxidants or iNOS inhibitors. Because of the frequency of this disease, its large economic impact, effects on welfare of chronically affected animals, and efforts to limit mass medication with antibiotics for disease prevention, effective methods to control Mycoplasma bovis infection or limit its harmful consequences would be of major benefit to the Ontario beef industry.
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