Investigations on the pathogenicity of Erysipelothrix rhusiopathiae in laying hens.

Erysipelas was diagnosed in 1998 from 34-wk-old laying hens in a free range flock in Germany. Erysipelothrix rhusiopathiae of serotype 1 was cultured from internal organs of the affected birds. This article describes the pathogenicity of the field isolate of E. rhusiopathiae in experimentally infected specific pathogen-free (SPF) laying hens. Three experiments were performed with SPF chickens inoculated at 17, 27, and 37 wk of age by either intramuscular (IM) or oral route. Inoculated birds were observed for 14 days. The highest mortality rates occurred in older birds, with 100% mortality observed in the 37-wk-old birds inoculated IM, 60% mortality reported in the younger 27-wk-old birds, and no mortality in the 17-wk-old age group. In the orally infected 27-wk-old birds, 40% mortality was detected, whereas no mortality was observed in the oldest birds by the same route. The results of the experiments support the contention that older birds are more sensitive to infection than younger birds and that mortality in laying hens is age related and dependent on the route of infection.