Identification of Leukotoxin and other vaccine candidate proteins in a Mannheimia haemolytica commercial antigen

Tucci, Paula; Estevez, Verónica; Becco, Lorena; Cabrera-Cabrera, Florencia; Grotiuz, Germán; Reolon, Eduardo; Marín, Mónica

Bovine Respiratory Disease (BRD) is one of the leading causes of death and economic loss for the beef and dairy cattle industry. It has an estimated annual cost to the worldwide cattle industry of over $3 billion (Potter, 2015) . This multifactorial syndrome can be caused either by viral or bacterial pathogens. Viral agents include bovine respiratory syncytial virus (BRSV) (Gershwin et al., 2000) , parainfluenza III virus (PI-3) (Fulton et al., 2000) , bovine viral diarrhea virus (BVDV) (Ridpath, 2010) and bovine corona virus (BCV) (Autio et al., 2007) . These respiratory viruses along with some mycoplasmal agents are generally the primary infectious agents involved in BRD (Potter, 2015) . This initial infection establishes a respiratory environment predisposing to the colonization and replication of pathogenic bacteria, including Mannheimia haemolytica (Al-Ghamdi et al., 2000) , Pasteurella multocida (Dabo et al., 2007) and Histophilus somni (Corbeil, 2007) , the former being responsible for up to 50% of the disease associated mortality (Narayanan et al., 2002; Potter, 2015) . M. haemolytica is a Gram negative opportunistic bacterium. Although it is a common bacterium of the upper respiratory tract and nasopharynx of healthy ruminants, it can also act as an opportunistic pathogen infecting the lower respiratory tract under stressful situations such as shipping, adverse environmental conditions or previous respiratory viral infection (Youssef et al., 2004; Orouji et al., 2012) .