The causal organism is Mycoplasma mycoides mycoides small colony type. (Also see Mycoplasma Pneumonias in Goats Mycoplasma Pneumonias in Goats 
.) Susceptible cattle become infected by inhaling droplets disseminated by coughing in affected cattle. Small ruminants and wildlife are not important in the epidemiology. Sheep and goats can be naturally infected but have no associated pathology. The organism can also be found in saliva, urine, fetal membranes, and uterine discharges. Transplacental infection of the fetus can occur. Viability of the organism in the environment is poor. The incubation period varies, but most cases occur 3–8 wk after exposure. In some localities, susceptible herds may show up to 70% morbidity, but much lower infection rates (~10%) associated with clinical signs are more common. Mortality is likely to be ~50% in herds experiencing the disease for the first time. Of recovered animals, 25% may become carriers with chronic lung lesions in the form of sequestra of variable size. Because carriers may not be detectable clinically or serologically, they constitute a serious problem in control programs. Breed susceptibility, management systems, and general health of the animal are important factors that influence the infection.
