Mycoplasma agalactiae is the aetiological agent of Contagious Agalactia (CA), an economically detrimental disease affecting small ruminants worldwide. The control of M. agalactiae through vaccination is an increasing challenge. Although several inactivated vaccines have proved effective in conferring protection against CA, they carry intrinsic disadvantages and only produce a short-lived humoral immune response. A DNA vaccine against CA has been developed encoding the P48eof Mycoplasma agalactiae inducing the immune responses in BALB/c mice (Chessa et al., 2009). In this study, the vaccinal plasmid pJW/tPA/rP48 expressing the P48 of M. agalactiae in fusion with the signal peptide of tissue plasminogen activator (tPA) was designed and evaluated in vivo. Initially, the production of P48 was evaluated in HEK 293 cells by rtPCR and by Western blotting. A field trial was performed by immunizing sheep by injecting them both with recombinant P48 protein and the plasmid pJW/tPA/rP48. Results demonstrated the production of P48-specific antibodies in immunized sheep, confirming that P48 was expressed and induced significant immune responses. Also we showed that immunization can negatively affect milk-shedding of microorganisms, especially when a prime boost strategy is used. Concluding, it has been demonstrated that even if immunization against rP48 alone induce a significant immune response it does not protect sheep against CA
