The absence of regional lymph nodes in birds, allows the frequent development of sepsis. The origin of the bacteria can be found in the yolk bag, in the food and farm (air or litter). The incubation time which elapses between infection and the appearance of the first symptoms or lesions, normally is long because of the high temperature, physiology of the birds retards the growth of bacteria. For this reason it is common to find the first lesions from 2 weeks age in yolk or from 3 weeks in food and environment.

In all cases one of the first lesions are petechiae in fat, thigh muscles or fat in the heart. To discard the mycotoxin origin, in the case of petechiae for sepsis bleeding should not occur in the large muscles of the thigh or chest muscles.