Prevalence of Dichelobacter nodosus and Ovine Footrot in German Sheep Flocks

SIMPLE SUMMARY: Footrot is a highly contagious foot disease in sheep and a common cause of lameness. It is a major challenge for sheep industries worldwide and has great economic impact on production. Due to the pain associated with the disease, it is considered an animal welfare issue. Footrot is caused by the bacterium Dichelobacter nodosus (D. nodosus), which encompasses benign and virulent strains. Benign D. nodosus commonly causes an inflammation of the interdigital skin whereas virulent strains can lead to severe footrot with a separation of hoof horn from the underlying soft tissue as the disease progresses. The objectives of this field study were to determine the prevalence of D. nodosus in a wide range of sheep flocks across Germany using swab samples from the interdigital skin of the feet. Due to the high prevalence of 42.93% of D. nodosus in the German sheep population, further work is required to determine measures on how to decrease the prevalence. ABSTRACT: The bacterium Dichelobacter nodosus (D. nodosus) is the causative agent of ovine footrot. The aim of this field study was to determine the prevalence of D. nodosus in German sheep flocks. The sheep owners participated voluntarily in the study. More than 9000 sheep from 207 flocks were screened for footrot scores using a Footrot Scoring System from 0 to 5 and sampling each sheep using one interdigital swab for all four feet of the sheep. The detection and discrimination between benign and virulent strains was done employing a real-time PCR. Our results showed a mean prevalence of 42.93% of D. nodosus in German sheep on an animal level. Underrunning of hoof horn on at least one foot (Scores 3-5) was detected in 567 sheep (6.13%). Sheep with four clinically healthy feet were found through visual inspection in 47.85% of all animals included in this study. In total, 1117 swabs from sheep with four clinically healthy feet tested positive for D. nodosus. In 90.35% of the positive swabs, virulent D. nodosus were detected. Benign D. nodosus were detected in 4.74% of the D. nodosus-positive swabs while 4.91% tested positive for both, benign and virulent D. nodosus. In 59 flocks D. nodosus were not detected and in 115 flocks only virulent D. nodosus were found while seven flocks tested positive for benign strains.