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A Disinfection Field Trial to Remove Bovine Digital Dermatitis Treponemes from Hoof Knives after Foot- Trimming
Gillespie, A.; Carter, S.; Blowey...
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Objectives: Although lameness caused by bovine digital dermatitis (BDD) is widespread and much researched, the mode of transmission has not been clarified. Hoof knives become contaminated with BDD treponemes during foot-trimming(1), and these bacteria may survive for up to two hours under aerobic conditions on hoof knife blades(2).
This study tested a protocol for disinfecting hoof knives to mitigate the risk of transmitting BDD during foot-trimming. Three disinfectants were previously identified as candidates for hoof knife disinfection in vitro using a 20 second contact time(2). The current study tests these three disinfectants: 1:100 FAM30®, 2% Virkon® and 2% sodium hypochlorite- under field conditions during foot-trimming.
Materials and Methods: This study was approved by the University of Liverpool Veterinary Research Ethics Committee (Ref: VREC662).
Samples were collected on three commercial farms during foot-trimming of 133 BDD-affected feet from lactating dairy cattle. Swabs were taken from each hoof knife before trimming (as a negative control) and after trimming. Knives were briefly rinsed in water to remove gross contamination, then the blade was submerged for 20 seconds in one of three disinfectants (1:100 FAM30®, 2% Virkon® and 2% sodium hypochlorite) or water only for comparison. A third swab was taken to provide post-disinfection samples. There was no hoof knife contact with the BDD lesion during trimming in 22 cases, whilst contact was made with the lesion in 111 cases for treatment purposes.
Detection of bacteria from the Treponema genus, and from three known BDD-associated pathogenic phylogroups, was undertaken via two methods. Nested PCR of sample swabs taken directly from the hoof knife blades, and nested PCR of samples extracted from cultures given six weeks to grow was carried out according to previously established protocols (2). The former method is more sensitive for detecting TreponemaDNA and the latter provides a measure of bacterial viability demonstrated by an ability to grow in liquid medium.
Results: Where direct contact was not made with BDD lesions during trimming, 12/22 (54.5%) of swabs taken from hoof knives were positive for at least one of the three pathogenic phylogroups after trimming using nested PCR. After disinfection 10/22 (45.4%) remained DNA positive. In terms of microorganism viability, pathogenic treponemes were detect- ed by nested PCR of cultures after six weeks in 1/22 (4.5%) of these cases after trimming, and disinfection using 2% Virkon® removed culturable organisms.
Where contact was made with BDD lesions (n= 111), 100% of swabs taken from hoof knives after trimming and tested directly were DNA positive for at least one of the three pathogenic phylogroups. After disinfection 38/111 (34.3%) of knives re- mained DNA positive. Pathogenic treponemes were detected by nested PCR of cultures after six weeks in 47/111 (42.3%) of cases after trimming. All three disinfectants (and water alone) were effective at removing culturable organisms (Table 1).
Conclusions: BDD-associated treponemes can be cultivated from hoof knives in 4.5% of cases after foot-trimming of BDD affected feet where no contact is made with the lesion. Where contact has been made with BDD lesions, BDD treponemes are culturable in 42.3% of cases. Rinsing hoof knives briefly in water then disinfecting the blades for 20 seconds in 1:100 FAM30®, 2% Virkon® or 2% sodium hypochlorite was shown to be effective for removing culturable BDD-associated treponemes from hoof knives.
Keywords: Digital dermatitis, Treponeme, Lameness, Foot-trimming, Disinfection.
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Affiliation of the authors at the time of publication
University of Liverpool, Institute of Infection and Global Health, United Kingdom;
Wood Veterinary Group, Gloucester, United Kingdom.
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