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Digital dermatitis (DD) is an ulcerative lesion of the bovine digital skin (Cheli and Mortellaro 1974) which causes severe lameness in dairy cattle. The disease can have considerable economic impact through reduced reproductive performance, weight loss and the costs of treatment and control. The primary causative agents of DD in dairy cattle are considered to be spirochetal bacteria of the genus Treponema (Evans and others 2011). Recently, the disease has been identified to be polytreponemal in aetiology (Klitgaard and others 2008), and in the UK and USA, three phylotypes have been isolated from dairy cattle lesions (Evans and others 2008, Stamm and others 2002), and described as ‘Treponema medium/Treponema vincentii-like’, ‘Treponema phagedenis-like’ and ‘Treponema denticola/T putidum-like’ BDD spirochaetes (Evans and others 2008) with the latter now recognised as a new species, Treponema pedis (Evans and others 2009).
DD has been reported in dairy cattle in nearly all countries where they are farmed, and the disease has spread to sheep in the UK (Harwood and others 1997). There have been anecdotal reports of DD lesions in beef cattle and of increased prevalence in recent years, but only the abattoir studies of Brown and others (2000) in southeast USA has actually reported the disease in beef cattle. There have been no definitive published case reports in the UK or elsewhere; these will be a prerequisite where a case definition is required.
Animals suspected of suffering from DD from two beef herds in Gloucestershire were assessed by the attending veterinary surgeon (RB). Farm 1 was a beef-rearing unit, with 120 beef cattle. The farm estimate was 25 animals per year (21 per cent) required treatment for DD. Farm 2 was a finishing unit and the farm estimate was 15/3000 animals were treated for DD each year (0.5 per cent). However, neither farm had true prevalence or incidence data, since at no time did all animals have their feet examined for typical lesions. Cases were treated topically, and records of treatments were not good.
On each farm, the animals suspected of suffering from DD, seven on farm 1 and five on farm 2, were examined, and following confirmation of DD on all animals, the foot was cleaned, lesions photographed and description of lesions noted.
Typical lesions presented as 30–60 mm diameter circular areas of brown moist exudate, primarily in the region of the caudal interdigital cleft, at the junction of the skin with the soft perioplic horn of the heel. Lesion cleaning revealed an underlying raw proliferative area with a stippled appearance. This was intensely sensitive to simple digital pressure. Fig 1a shows a mild/early lesion and Fig 1b is of a more severe lesion undergoing proliferative change. In another case, lesions also occurred on the anterior coronary band; this can lead to disruption of hoof wall formation. Occasional lesions extended into the interdigital cleft, sometimes on the surface of interdigital skin, leading to interdigital hyperplasia, or extended dorsally to the accessory digits. In all cases, the primary clinical sign was lameness. On these farms, simply lifting and cleaning the affected area, application of topical antibiotic held in place with a dressing for 2–3 days, in most cases, resulted in uneventful recovery. Recovery periods were not recorded. In herd outbreaks, prevention and control on farm 1 was achieved by daily foot bathing in 5 per cent formalin.
Four of the beef cattle lesions (n=4) were identified at the classical ulcerative stage defined as ‘M2’ grade lesions (Döpfer and others 1997). The centre of the lesion was biopsied using a 3 mm punch biopsy under local anaesthesia (Evans and others 2008). From farm 1, samples 1 and 2 were taken from Aberdeen Angus cross Friesian males. From farm 2, samples 3 and 4 were from a crossbred Simmental heifer and a Hereford cross Friesian heifer, respectively. All samples for PCR analysis were transported on ice and later stored at −20°C. Bacterial isolation of tissues and DNA extraction from treponeme cultures was performed as described previously (Evans and others 2008).
For PCR analysis, tissues from DD lesions were thawed and DNA extracted using a Dneasy kit (Qiagen, UK) according to the manufacturer's instructions, and genomic DNA stored at −20°C. Samples were subjected to nested PCR specific for the three BDD treponeme groups described by Evans and others (2008, 2009) with resulting fragments encompassing 300–500 bp of the 16S rRNA gene. All samples were subjected to the Treponema genus-wide PCR test as described by Moore and others (2005).
The four DD samples obtained were positive for the Treponema genus-specific PCR (Table 1) which detects all Treponema species including pathogenic and commensal spirochaetes. In the BDD group-specific PCRs, three of the four samples were positive for T medium/T vincentii-like spirochaetes, and three of four positive for T pedis. All were positive for Treponema phagedenis-like BDD spirochaetes (Table 1).
Spirochaetes were successfully isolated from lesion sample 1 and 16S rRNA gene sequencing were carried out as previously described (Evans and others 2008).
The isolate G498P (Genbank accession: KC907379) was identified as belonging to the T phagedenis-like spirochaetes, and shared 100 per cent 16S rRNA gene sequence identity with T phagedenis strain T320A (Genbank accession: EF061261), previously isolated from a dairy cow (Evans and others 2008).
The clinical presentation of DD in beef cattle is identical to lesions found in dairy cattle DD. However, some cases (observed by RB) progress to more severe lesions. The presence of previously reported DD-associated Treponema phylotypes in the lesions tested thus far suggests they have the same or similar aetiology as dairy cattle DD, and it appears that all three BDD Treponema phylotypes play a role in the lesions. Brown and others (2000), in the USA, reported digital dermatitis lesions in 4 per cent of beef cattle in their abattoir study and clinical observations by veterinarians/farmers in the UK suggest that DD prevalence rates within beef herds seem to be varied. However, data from Brown and others (2000), along with estimates of farm prevalence on the two farms used in this study, appears to suggest a lower within-herd prevalence rate than is commonly found in dairy cattle. Dairy cattle estimates have been found to be between 20 and 30 per cent (Brown and others 2000, Cramer and others 2008, Barker and others 2009) and a more recent study found lesions in 460/742 (62 per cent) of dairy cattle (Nielsen and others 2012). Research is needed to further investigate within-herd DD prevalence rates in beef cattle. Additionally, investigations are proceeding to fully identify the Treponema phylotypes involved in beef cattle DD.
The authors would like to thank the farms involved in this work and the funders, EBLEX, HCC and QMS, who made this work possible.
Provenance: not commissioned; externally peer reviewed
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