The work reported in this research communication investigated the occurrence of Mycoplasma bovis (M. bovis) in milk samples from cows with clinical mastitis on dairy farms from seven Brazilian states. We hypothesized that M. bovis was present in bovine clinical mastitis milk in Brazil. A total of 561 milk samples were cultured on Hayflick agar and incubated in a microaerophilic atmosphere at 5% CO2. Polymerase chain reaction (PCR) was performed for the detection of Mycoplasma spp. and Mycoplasma bovis in milk samples. Mycoplasma spp. were isolated in 2% of the milk samples, and Mycoplasma bovis was verified in 3% of the milk samples by PCR. The results showed that Mycoplasma bovis is involved in clinical mastitis in Brazilian dairy herds. We emphasize the need for further studies to investigate the infection by this agent in clinical mastitis cases, particularly in Brazil, due to the lack of knowledge about its prevalence.

Mannheimia haemolytica, Pasteurella multocida, Histophilus somni, Mycoplasma bovis and Arcanobacterium pyogenes are all frequently implicated in bovine respiratory disease (BRD). M. haemolytica is considered the most important of the group. These bacteria are commensals in the nasopharynx and establish infection in the lungs of cattle that are subjected to a variety of stresses. Factors that permit adherence to and proliferation in the lungs and factors that cause tissue destruction and inflammation have been identified as having major roles in pathogenesis. These virulence factors include protein adhesins, capsular polysaccharide, outer membrane proteins, iron-binding proteins, lipopolysacharide or lipooligosaccharide, enzymes and toxins. These bacterial products function to evade the immune system, damage the immune system and induce a severe inflammatory response.

Mycoplasma bovis is an important and emerging cause of respiratory disease and arthritis in feedlot cattle and young dairy and veal calves, and has a variety of other disease manifestations in cattle. M. bovis is certainly capable of causing acute respiratory disease in cattle, yet the attributable fraction has been difficult to estimate. In contrast, M. bovis is more accepted as a cause of chronic bronchopneumonia with caseous and perhaps coagulative necrosis, characterized by persistent infection that seems poorly responsive to many antibiotics. An understanding of the disease has been recently advanced by comparisons of natural and experimentally induced disease, development of molecular diagnostic tools, and understanding some aspects of virulence, yet uncertainties regarding protective immunity, the importance of genotypic diversity, mechanisms of virulence, and the role of co-pathogens have restricted our understanding of pathogenesis and our ability to effectively control the disease. This review critically considers the relationship between M. bovis infection and the various manifestations of the bovine respiratory disease complex, and addresses the pathogenesis, clinical and pathologic sequelae, laboratory diagnosis and control of disease resulting from M. bovis infection in the bovine respiratory tract.