To the Editor,
Bovine digital dermatitis (BDD) is a major infectious cause of lameness in both beef and dairy cattle worldwide, with significant welfare and economic implications. Pathogenic spirochaetes belonging to the genus Treponema are highly associated with the BDD lesion and are considered essential to its aetiology. BDD transmission routes have yet to be fully defined, although transmission via unsterilized foot trimming equipment, and in particular, trimming blades, is supported by epidemiological data: Wells et al. (Reference Wells, Garber and Wagner1999) demonstrated that a failure to clean trimming blades between cows was associated with a high (>5%) herd incidence of BDD (Odds Ratio 1.9). Recent research undertaken by our group has demonstrated that blades used to trim BDD-symptomatic feet readily become contaminated with the BDD-associated treponeme DNA and cultivatable cells (Sullivan et al., Reference Sullivan, Blowey, Carter, Duncan, Grove-White, Page, Iveson, Angell and Evans2014). Moreover, we have shown that under aerobic conditions, treponeme viability on foot trimming blades is maintained for up to two hours (Gillespie et al., Reference Gillespie, Carter, Blowey and Evans2019), which may facilitate both intra- and inter-herd transmission. To mitigate the risk of BDD transmission via this route, disinfection of the foot trimming blades should be considered.
Previously, an in vitro evaluation of several footbath disinfectants against a BDD treponeme isolate (Treponema phagedenis-like) revealed that the minimum inhibitory concentrations and minimum bactericidal concentrations remained below working disinfectant concentrations (Hartshorn et al., Reference Hartshorn, Thomas, Anklam, Lopez-Benavides, Buchalova, Hemling and Döpfer2013). In addition, this activity persisted despite up to 20% manure contamination, implying that effective concentrations could be achieved practically on farm. Recently, we investigated the disinfection efficacy of popular disinfectants against BDD-associated treponemes on foot trimming blades in vitro and demonstrated that a 20 s contact with 1% FAM®30, 2% Virkon® or 2% sodium hypochlorite rendered treponemes non-viable (Gillespie et al., Reference Gillespie, Carter, Blowey and Evans2019), effectively eliminating the potential for transmission.
With these data, we have developed a standardized blade disinfection protocol which we recommend as part of a holistic approach to BDD infection control. The disinfection protocol, to be applied during foot trimming, is available online at: https://ahdb.org.uk/reducing-spread-of-DD
