PASTEURELLA-HAEMOLYTICA COMPLICATED RESPIRATORY-INFECTIONS IN SHEEP AND GOATS

Respiratory infections which commonly occur in sheep and goats often r esult from adverse physical and physiological stress combined with vir al and bacterial infections. Inevitably, Pasteurella haemolytica pneum onia occurs as a result of these interactions. In this review, we pres ent recent advances in research on the complex etiology of pneumonia i nvolving P. haemolytica ica. Initially stress, induced by factors such as heat, overcrowding, exposure to inclement weather, poor ventilatio n, handling and transport is a major predisposing factor. Respiratory viruses including parainfluenza 3 (PI-3) virus, adenovirus type 6 and respiratory syncytial virus (RSV), and to a lesser extent bovine adeno virus type 2, ovine adenovirus types 1 and 5, and reovirus type I caus e respiratory infections and pneumonia. More importantly these viruses also dramatically increase the susceptibility of sheep and goats to s econdary P. haemolytica infection. Primary infection of the lower resp iratory tract, with Mycoplasma ovipneumoniae and Bordetella parapertus sis can increase the susceptibility of sheep and goats to secondary P. haemolytica infection. It is possible that initial infections with vi ral or primary bacterial agents break down the antimicrobial barrier c onsisting of beta defensins and anionic peptides found in epithelial c ells, resident and inflammatory cells, and serous and mucous secretion s of the respiratory tract. Loss of barrier integrity may release P. h aemolytica from its usual commensal status. Once in the lung, P. haemo lytica becomes opportunistic. To grow and colonize, P. haemolytica use s extracellular products like O-sialoglycoprotein endopeptidase, neura minidase and RTX leukotoxin, as well as cell-associated products such as capsular polysaccharide, lipopolysaccharide, outer membrane protein s, proteins involved in iron acquisition and a periplasmic superoxide dismutase. In lambs and kids, pneumonic pasteurellosis can be acute, c haracterized by fever, listlessness, poor appetite and sudden death. S heep and goats that survive the acute stage may recover or become chro nically affected showing reduced lung capacity and weight gain efficie ncy and sporadic deaths may occur. This infection is detrimental to sh eep and goats throughout the world and flocks and herds of small ranch es, dairy operations, or large feedlots are all affected. (C) Inra/Els evier, Paris.