Pneumonic mannheimiosis and pasteurellosis of cattle

Previous author: D C Hodgins and P E Shewen

Current authors:
Anthony W. Confer, DVM, PhD, Diplomate ACVP,Regents Professor & Sitlington Endowed Chair, Oklahoma State University, Stillwater, Oklahoma, USA
J D, TAYLOR, Professor, DVM, MPH, PhD, DACVIM (LA), DACVPM, Veterinary Pathobiology, College of Veterinary Medicine, Oklahoma State University, United States

Introduction

Pneumonic pasteurellosis by definition refers to infection of the lung(s) with organisms of the genus Pasteurella.³¹ The term pneumonic pasteurellosis has served conveniently since the 1960s^{29, 220} as a means of speaking collectively of pneumonias caused by Pasteurella haemolytica and Pasteurella multocida without committing oneself as to the relative importance of the two agents. With the reclassification of P. haemolytica biotype A strains as Mannheimia haemolytica,¹¹ pneumonic pasteurellosis is an inappropriate name for pneumonia caused by both agents; however, its use is still widespread. The terms pneumonic mannheimiosis and pneumonic pasteurellosis should be used to separate the diseases caused by the two bacteria, M. haemolytica and P. multocida, respectively.

Although these organisms can cause disease in young calves (as a component of enzootic pneumonia of beef, dairy, and veal calves,^{5, 92, 148, 276} pneumonic mannheimiosis and pasteurellosis are a far greater problem in recently weaned beef calves shortly after entry to feedlots or after long shipments of various kinds as a component of ‘shipping fever’ or undifferentiated bovine respiratory disease (BRD).^{138, 184, 190, 192, 290} Economic losses to the North American feedlot industry due to respiratory disease have been estimated to be as high as one billion dollars annually,²⁸³ and losses to the beef industry in the UK have been estimated at 70 million pounds annually.^{135, 206} Morbidity rates of 15 to 45 per cent and mortality rates of 1 to 5 per cent are common in newly received feedlot calves;¹⁴⁴ it is estimated that 75 per cent of the morbidity¹²⁵ and 50 to 60 per cent of the mortality⁷⁸ are attributable to respiratory disease. The major bacterial pathogen involved in beef cattle respiratory disease is M. haemolytica, whereas P. multocida is less frequently involved, but is often the major pathogen in young dairy calf pneumonia.^{189, 278} In spite of continuing intensive research to develop efficacious vaccines and improved management programmes to prevent pneumonic pasteurellosis in feedlot cattle, success to date has been limited and control of bovine bacterial pneumonia still relies heavily on antibiotics as preventative measures and for treatment.²¹

Aetiology

Mannheimia haemolytica and P. multocida are Gram-negative, non-motile, non-spore-forming, fermentative, oxidase- positive, facultative anaerobic short rods or coccobacilli of the family Pasteurellaceae.^{117, 217} Bipolar staining can be demonstrated using Wright's stain. Both grow best in media supplemented with serum or blood; M. haemolytica grows on MacConkey agar, but P. multocida does not. After 24 hours’ incubation on bovine or ovine blood agar plates, colonies of M. haemolytica are round and greyish, with a variable area of ß haemolysis, which can be small, requiring scraping of the colony from the agar to visualize. Colonies of P. multocida are generally round, greyish and non-haemolytic with more heavily encapsulated strains appearing mucoid.^{117, 217, 224}

Mannheimia haemolytica was originally named Pasteurella haemolytica, and two biotypes, A and T, along with 17 serotypes and numerous untypable strains were identified.^{88, 251} In 1990, biotype A strains were found related by DNA homology, and biotype T strains were related; however, biotype A and T strains had little genetic relationship.²⁷ Biotype T strains became Pasteurella trehalosi and later Bibersteinia trehalosi.^{28, 252} Through DNA–DNA hybridization and 16S rRNA sequencing, all but one of the A biotypes were designated M. haemolytica. (Angen et al., 1999) Therefore, M. haemolytica consists of the previous P. haemolytica biotype A Serotypes 1,2,5-9, 12-14, 16 and 17.¹⁴² Because all M. haemolytica serotypes are derived from biotype A, the designation of M. haemolytica serotypes as A1, A2, etc., often continues, even though it is redundant to include the biotype designation. Serotypes 1 and 6 are the most commonly isolated from BRD.²²⁴

Pasteurella multocida has been classified into 5 serogroups (A, B, D, E and F) based on capsular polysaccharide antigen and 16 serotypes (1-16) based on lipopolysaccharide.^{39, 227} Most P. multocida isolated from bovine respiratory disease are A serogroup, with A:3 being the most common.⁶⁶

The importance of M. haemolytica and P. multocida in pneumonia of feedlot cattle was suspected in early studies because of their frequent isolation from clinical cases and necropsy specimens. Doubts arose, however, as to whether these agents were primary pathogens, due to difficulties in reproducing clinical disease and pulmonary lesions experimentally and because bacterins did not mediate protection. Identification of numerous pathogenic bovine respiratory viruses that cause lesions or impair clearance of bacteria from the lower respiratory tract encouraged the view that infection with viruses or perhaps Mycoplasma spp., especially Mycoplasma bovis,¹⁰² was a necessary prelude to pneumonia with M. haemolytica or P. multocida. Bovine herpesvirus 1...