Field and experimental studies of bovine pneumonic pasteurellosis

Abstract

The condition known as shipping fever was a severe source of financial loss to the beef industry in North America, where it was regarded as being a disease in which stress or viral infection preceded a severe pneumonic pasteurellosis. In Britain, a similar disease, transit fever, was recorded but no extensive research had been conducted into the condition. In these studies 29 incidents of acute respiratory disease, described as transit fever, were investigated in single-suckled calves, 24 of these were in recently housed single suckled calves and five in single suckled calves at foot with their dams. All the incidents occurred within 24 days of housing, irrespective of whether they were homebred or purchased and all but one of the incidents occurred between October 1 and December 31. In 20 of the incidents in weaned calves the disease was confirmed on clinical, microbiological and pathological grounds as a pneumonic pasteurellosis. Pasteurella haemolytica Al was recovered from slaughtered clinical cases of the disease in 18 of these incidents. The four other incidents which presented clinically as transit fever could not be confirmed as pneumonic pasteurellosis on either microbiological or pathological grounds. The five incidents in singlesuckled calves at foot were all confirmed as pneumonic pasteurellosis, three associated with P. haemolytica Al and two with P. haemolytica T10. Diagnosis of pneumonic pasteurellosis was based on the clinical findings of dullness, inappetence, pyrexia and pneumonia, usually with minimal coughing, isolation of Pasteurella spp. from a number of sites in the upper and lower respiratory tracts, and a distinctive pathology including consolidation, fibrinous pneumonia which could be diffuse or focal (nodules), fibrinous pleurisy and gross dilatation of the interlobular septa. Examination of the affected cattle at post-mortem did not demonstrate the regular presence of viral or other microbiological agents at any stage of the disease process. The examination of nasopharyngeal swabs and paired serology from groups of cattle in-contact with the cases of confirmed pneumonic pasteurellosis indicated that although there was sometimes seroconversion to viruses known to cause respiratory disease (PI3 and RS viruses) this was not a consistent feature, and similar numbers of seroconversions were seen in monitor groups of similar calves in which no respiratory disease occurred. Similarly, the presence of P. haemolytica Al in the nasopharynx and seroconversion to that organism within a group of suckled calves were at similar levels in groups of calves in which pneumonic pasteurellosis had been confirmed and those in which no respiratory disease had occurred. The development of an experimental model was attempted using stationary phase cultures of an isolate of P. haemolytica Al, from an incident of confirmed bovine pneumonic pasteurellosis,together with P13 virus infection or hormonal and physical stress. Pneumonic pasteurellosis was not produced. However, the use of a log phase culture of P. haemolytica Al in the absence of other infectious or stressor agents was successful. Calves were inoculated intranasally and intratracheally and the clinical signs seen were indistinguishable from those seen in field cases of confirmed pneumonic pasteurellosis. At post-mortem the infecting strain of P. haemolytica Al was recovered in large numbers throughout the upper and lower respiratory tract and the pathology was indistinguishable from that seen in the field cases of confirmed pneumonic pasteurellosis. As a result of these investigations it has been shown that transit fever as it occurs in Scotland is almost exclusively a primary pneumonic pasteurellosis