Pathological importance of Mannheimia haemolytica in ruminants: Literature review

Abstract

The aim of this work was to summarise the characteristics of the bacterium M. haemolytica, and the pathogenesis, pathology, prevention and control of diseases caused by it with respect to the bovine, ovine and caprine species. As discussed above, M. haemolytica has recently been reclassified. Although the bacterium has been well known for a long time, its taxonomic position was clarified only a few years 32 ago. M. haemolytica includes serotypes 1, 2, 5-9, 12-14, 16 and 17 of the former P. haemolytica (Blackall et al., 2002). M. haemolytica is a common opportunistic agent in the nasopharynx of cattle, sheep and goats, which can infect animals with a weakened pulmonary defence and colonize the lungs rapidly (Rhemtulla and Thomson, 1981). Although M. haemolytica has been isolated worldwide, the prevalence of the disease strongly correlates with Western animal management practices that include overcrowding and transport (Highlander, 2001). A morbidity rate of 15- 45 % and a mortality rate of 1-5% rising to 10% depending on the speed with which treatment is initiated, has been described in most reports of shipping fever (Jubb et al., 2007). In the US, the economic losses due to shipping fever pneumonia surpass the combined cost of all other diseases of cattle (Highlander, 2001). Shipping fever is economically a very significant disease of cattle resulting in approximately 30 % of all cattle death globally and in the US alone causes an annual economic loss of 1 billion US $ (Griffin, 1997). Prevention of M. haemolytica infection and disease can be achieved by three means: first, by prophylactic administration of antimicrobials to animals at high risk of contracting the disease; second, by increasing the immunity of the host by ensuring adequate passive transfer and treatment with vaccines against M. haemolytica (as mentioned above in section 2.4); and third, by decreasing the predisposing factors which are linked with the infection and disease caused such as viral respiratory tract infection, mixing of animals from different sources, and long distance shipment (Smith, 2009). Although today improved vaccines are available, protection by these vaccines is not absolute. Antimicrobials can be used conjunctively to resolve this problem and control bacterial infection. However, common use of antimicrobials in treatment and growth promotion can lead to antimicrobial resistant bacteria (Katsuda et al., 2009). Indeed, recent M. haemolytica isolates from animals with BRD have revealed increasing proportions to be resistant to antimicrobials. This increased frequency of antimicrobial resistance has become a major public health and animal health concern. 33 In the light of this study, it is evident that M. haemolytica is a serious pathogen, either alone or in combination, and that continued efforts and research are warranted to address its prevention and/or treatment.