Dichelobacter nodosus
[2] D. nodosus, along with Fusobacterium necrophorum, co-exist as the causative agents of ovine foot rot and interdigital dermatitis in ungulates globally, especially in temperate zones.
[6][7] Treatment options include footbaths, parenteral administration of long-acting antimicrobials, concurrent use of vaccines, and removal of affected sheep into a clean, quarantined area.
[6] D. nodosus is a rod shaped, gram negative, anaerobic obligate bacteria found on hooves which causes ovine foot rot.
[17] The primary obligate agent for causing disease is D. nodosus, although F. necrophorum has been reported as having synergistic effects in severe cases of foot rot.
[17][19][20] D. nodosus has a global distribution year-round with characteristic highly transmissible peaks occurring in temperate zones where there is adequate moisture and an ambient temperature above 10 degrees.
[21] In order for D. nodosus to cause disease the bacterium requires irritation to the interdigital space, this can be due to moisture or trauma to the area.
[6][7] In Australia, the difference between benign or virulent is dependent on the causative strain of D. nodosus acquired foot rot and is associated with the degree of severity of the clinical signs.
[23][6][7] Clinical signs of virulent foot rot begin as interdigital dermatitis but progress to necrosis, separation of the hoof wall from the underlying soft tissue and severe lameness.
[6] However, both categories of foot rot can progress from interdigital dermatitis to more severe, chronic, necrotizing lesions that can have a characteristic putrid smell and cause significant lameness in the affected animal.
[6][7] Use of a foot rot scoring guide to help confirm diagnosis and to determine the severity of the disease as well as level of treatment and management that will be required.
[6][3][9][10] This includes immediate treatment upon identification, foot-baths, parenteral administration of long-acting antimicrobials, concurrent use of vaccines, and removal of affected sheep into a clean, quarantined area.
[6][3][8][9][10] The prognosis for foot rot is best when treated early, prior to progression of the disease; this helps guide the decision between treatment versus culling of affected animals in order to minimize economic losses.
[6][3][10][9] Affected sheep should be monitored to ensure effectiveness of treatment and culled if clinical symptoms persist, as they are a source of contamination for the rest of the flock.
[10][9][6] The use of foot bathes containing 10% zinc sulphate solutions have shown to be effective in both treatment and prevention, though use is controversial due to environmental impacts.
[10][9][3][6] This bacterium has also shown sensitivity to tetracyclines, macrolides, penicillin, cephalosporins, and fluoroquinolones; with recent studies advocating for the efficacy of gamithromycin as an alternative to oxytetracycline.
[10][3] The use of antimicrobials is limited due to macrolides being of importance within human medicine, and withdrawal rates can impede economic returns and therefore their choice as a treatment option.
[3] Early identification of D. nodosus, as well as routine prevention will contribute to reduced reliance on antimicrobials, as well as less stress on emerging resistance, and economic losses.
[6][3] Once the environment is decontaminated, outbreaks can be prevented by ensuring replacement stock come from a verified source and are quarantined upon arrival until they test negative.
[8][3][6] In areas with endemic reports of the disease, a vaccine protocol is also effective in reducing incidence within a flock and concurrent use with infection will aid recovery time.
