General Information: This bacterium causes a contagious disease of cattle causing respiratory disease, mastitis, and arthritis. It is found worldwide and is inherently resistant to certain groups of antibiotics because it does not possess a cell wall. More recently, this species has become resistant to tetracycline, tilmicosin and spectinomycin which have been traditionally used in its control. The disease is spread between herds by the transfer of infected but seemingly healthy animals which shed viruses. It has also been introduced into healthy herds via frozen semen collected from an infected bull. The economic losses and negative impact on international trade from this disease have been considerable, and efforts are now underway to develop a vaccine.