Possible cross-infection of Dichelobacter nodosus between co-grazing sheep and cattle

BACKGROUND The aim of this study was to investigate possible cross-infection of Dichelobacter nodosus in Norwegian farms practising co-grazing of sheep and cattle. METHODS Thirteen farms practising co-grazing of sheep and cattle were included in this descriptive study: five farms with a history of severe ovine footrot (Group I) and eight farms with free-stall housing of cattle and signs of mild or no footrot in sheep (Group II). Sampling for PCR detection of D. nodosus was performed from animals in all farms, and clinical claw examination of sheep and cattle was performed in Group II. D. nodosus positive samples were analysed by a multiplex PCR method that detects variants of the fimA gene corresponding to D. nodosus serogroups A through I. RESULTS D. nodosus serogroup A was identified more frequently in sheep from farms with a history of severe footrot (Group I) versus from Group II, and in most of the farms with a history of severe footrot there was a coexistence of D. nodosus serogroup A in sheep and cattle. In one farm heel horn erosion and dermatitis emerged in cattle after co-grazing with sheep suffering from severe footrot where D. nodosus serogroup A was detected. Six months later heel horn erosion and dermatitis were still diagnosed, and D. nodosus serogroup A was identified. Out of the 16 D. nodosus positive sheep samples from Group II, ten of the samples were positive by the fimA serogrouping PCR. Among these 10 samples all serogroups except G were detected. All the D. nodosus serogroups detected in sheep were also present in the corresponding cattle herds. CONCLUSION The clinical findings and the coexistence of the same serogroups in co-grazing sheep and cattle could indicate cross-infection. However, further research including isolation of the bacterial strains, virulence-testing and genetic identification, is needed.