Abstract
BackgroundIn 2008, an outbreak of ovine footrot occurred in Norway. Dichelobacter nodosus isolates collected between 2008 and 2011 have been characterised. Isolates defined as virulent by the gelatin gel test (GG-test) were only found in sheep in Rogaland County, where the severe cases of footrot were registered. The majority (96%) of the virulent isolates belonged to serogroup A. It is suspected that they represent a newly introduced strain, and the aim of the present study was to investigate whether they are genetically similar. Sixty-one virulent isolates from sheep and 116 benign isolates from sheep, cattle and goats were included. Four GG-test virulent isolates from Danish sheep were also included. All isolates were genotyped by pulsed-field gel electrophoresis (PFGE) and by PCR for pgr variant determination.ResultsThe Norwegian virulent isolates were assigned to 8 pulsotypes (PTs), while the benign isolates were assigned to 66 PTs. Thirty-seven (68.5%) of the 54, virulent, serogroup A isolates belonged to the same PT, and included isolates from 2008 through 2011. Isolates belonging to this PT were defined as the outbreak strain. The remaining virulent serogroup A isolates belonged to 4 PTs differing by ≤3 bands from the outbreak strain. Two virulent, Danish, serogroup A isolates differed by 2 bands from the Norwegian outbreak strain. All but 3 (95%) of the virulent isolates had the pgrA variant while 85% of the benign isolates had the pgrB variant.ConclusionThis study provides evidence that the footrot outbreak in Norway in 2008 most likely was caused by new introduction and local spread of one virulent D. nodosus strain.
Highlights
In 2008, an outbreak of ovine footrot occurred in Norway
pulsed-field gel electrophoresis (PFGE) The 177 Norwegian D. nodosus isolates were divided into 74 different pulsotypes (PTs), consisting of 5–11 bands
The benign isolates were assigned to 66 PTs that clustered with >58% similarity and virulent isolates were assigned to 8 PTs that clustered with >72% similarity (Figure 1)
Summary
Dichelobacter nodosus isolates collected between 2008 and 2011 have been characterised. Isolates defined as virulent by the gelatin gel test (GG-test) were only found in sheep in Rogaland County, where the severe cases of footrot were registered. The severity of lesions depends on the virulence of the infecting bacterial strain, climatic conditions and the breed of sheep [3]. D. nodosus isolates from sheep, cattle and goats collected between 2008 and 2011 from different geographic locations in Norway were characterised with respect to virulence and serogroup [4]. Isolates that produced heat stable proteases, as shown by the gelatin gel test (GG-test) [5], were defined as virulent and were only found in sheep in the county of Rogaland where the most severe cases of footrot were registered.
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