Date Published: March 29, 2012
Publisher: BioMed Central
Author(s): Torunn Rogdo, Lisbeth Hektoen, Jannice Schau Slettemeås, Hannah Joan Jørgensen, Olav Østerås, Terje Fjeldaas.
The aim of this study was to investigate possible cross-infection of Dichelobacter nodosus in Norwegian farms practising co-grazing of sheep and cattle.
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.
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.
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.
Ovine footrot is a major cause of lameness in sheep worldwide . For 60 years the disease was considered eradicated in Norway, but in the spring of 2008 footrot was reported . Until then, ovine foot problems were paid relatively little attention to by farmers and veterinarians, although lameness had been a main reason for culling in some flocks . In a flock health study performed in 2007-2008, Dichelobacter nodosus was detected by PCR in two sheep flocks with mild or no clinical symptoms and in one flock where several animals were suffering from lameness . This initiated surveillance and clinical examination of 3300 sheep flocks where animals from about 1000 flocks were sampled [4,5]. D. nodosus was detected by PCR in more than 500 of these flocks, whereas only about 50 flocks were severely affected. The majority of the D. nodosus positive flocks had mild or no symptoms of footrot.
In our study of Norwegian farms practising co-grazing of sheep and cattle, D. nodosus belonging to serogroup A was prevalent in sheep in farms with a history of severe footrot (Group I). The study also demonstrates the coexistence of D. nodosus serogroup A in sheep and cattle, and the study of events indicates that the infection lasted longer than 6 months in one cattle herd. In the study of farms practicing free-stall housing of cattle and having sheep showing symptoms of mild or no ovine footrot (Group II), all the serogroups found in the sheep flocks were also found in the corresponding cattle herds. The clinical findings and the coexistence of the same serogroups in co-grazing sheep and cattle indicate cross-infection. However, further research including isolation of the bacterial strains, virulence-testing and genetic identification, is needed.
The authors declare that they have no competing interests.
TR contributed to the design of the study. She visited the farms and performed all the clinical recordings and sampling for PCR analyses. She performed the data analyses and also made the draft of the manuscript. LH contributed to the study design, the selection of farms, the analyses of data and the writing of the manuscript. JS established the laboratory methods and performed the analyses. HJJ contributed to data interpretation and to writing of the manuscript. TF contributed to the design of the study and to the writing of the manuscript. He was the main supervisor for TR in the present study during the field recordings and sampling, the analyses of the data and the writing period. All authors read the manuscript several times and approved the final manuscript.