Submitted to: Veterinary Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 12, 1997
Publication Date: N/A
Interpretive Summary: Respiratory tract diseases are a leading cause of loss from disease in the cattle, sheep and goat industries. Annual loss in the United States is estimated to exceed one billion dollars. Losses are from mortality, reduced feed efficiency, and slaughter condemnations, as well as prevention and treatment measures. Currently, not all the factors leading to the development of pneumonia are known by scientists and veterinarians. As part of our ongoing studies to understand the disease process, the factors initiating the onset of respiratory infection in sheep and goats were reviewed. Initially stress, previous respiratory viral infection, or preexisting bacterial infection can predispose animals to secondary bacterial pneumonia caused by Pasteurella haemolytica. To grow and colonize, P. haemolytica uses enzymes, toxins, and proteins to cause lung tissue damage. In lambs and kids, pneumonia can be acute, characterized by fever, listlessness, poor appetite and sudden death. Sheep and goats which survive the acute stage may recover or become chronically affected showing reduced lung capacity and weight gain efficiency and sporadic deaths may occur. Corollary benefits include an increase in the profitability and international competitiveness of the U.S. cattle industry, a stronger rural economy, and a continued supply of inexpensive, wholesome beef, and beef products for the American consumer.
Technical Abstract: Respiratory infections which commonly occur in sheep and goats often result from adverse physical and physiological stress combined with viral and bacterial infections. Inevitably, Pasteurella haemolytica pneumonia occurs as a result of these interactions. In this review, we present recent advances in research on the complex etiology of pneumonia involving P. haemolytica. Initially stress is major predisposing factor. Respiratory viruses (parainfluenza 3 virus, adenovirus, and respiratory syncytial virus) dramatically increase the susceptibility of sheep and goats to secondary P. haemolytica infection. Also, primary infection, with Mycoplasma ovipneumoniae and Bordetella parapertussis can increase the susceptibility of sheep and goats to secondary P. haemolytica infection. Once in the lung, P. haemolytica becomes opportunistic. To grow and colonize, P. haemolytica uses extracellular proteases, enzymes, and toxins as well as cell-associated products like capsular polysaccharide, lipopolysaccharide, and membrane-associated proteins. In lambs and kids, pneumonic pasteurellosis can be acute, characterized by fever, listlessness, poor appetite and sudden death. Sheep and goats which survive the acute stage may recover or become chronically affected showing reduced lung capacity and weight gain efficiency and sporadic deaths may occur. This infection is detrimental to sheep and goats throughout the world and flocks and herds of small ranches, dairy operations, or large feedlots are all affected.