Dichelobacter nodosus

Dichelobacter nodosus
Scientific classification
Domain:	Bacteria
Phylum:	Proteobacteria
Class:	Gammaproteobacteria
Order:	Cardiobacteriales
Family:	Cardiobacteriaceae
Genus:	Dichelobacter
Species:	D. nodosus
Binomial name
Dichelobacter nodosus (Beveridge 1941) (Mraz 1963) Dewhirst et al. 1990

Dichelobacter nodosus, formerly Bacteroides nodosus, is a Gram-negative, obligate anaerobe of the family Cardiobacteriaceae. It has polar fimbriae and is the causative agent of ovine foot rot as well as interdigital dermatitis. It is the lone species in the genus Dichelobacter.

Epidemiology

Foot rot is one of the top five globally important diseases acquired by sheep. 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. Outbreaks have been reported in Australia, Britain, Norway, Switzerland.

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. In cooler conditions, such as spring and autumn, higher disease prevalence can be observed in the UK and Ireland. This bacterium has the ability to thrive in moist soil for up to two weeks. In the presence of optimal conditions, the bacterium can live up to 24 days in at least 5 degrees Celsius. In suboptimal conditions, animals will not demonstrate full clinical presentation and mild lesions may be confined to the interdigital skin. Detection of a lower prevalence and persistence occurs in dry warm climates compared to wet cool conditions.

Sheep and goats are the main species affected by the bacterium and are susceptible at all ages. Merino breeds appear to be more susceptible over British breeds of sheep. British breeds appear to carry more natural resistance, displaying mild clinical signs of a short duration. Although, first cross offspring under the correct conditions can develop severe clinical disease. Cattle can become affected, although normally only suffer a mild form of infection. Wild ungulates have been reported to carry the bacterium in Germany and Switzerland .

There are challenges associated with isolating D. nodosus as more molecular-based studies need to be conducted to differentiate persistence in a domesticated farm environment.

Merino Sheep which are more susceptible to foot rot.

Disease

Clinical signs of foot rot in sheep can be divided into two categories; benign and virulent . 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. It can be difficult to tell the difference between the two strains based on clinical signs, some countries, such as the USA, consider both the benign and virulent strains the same and treat according to clinical presentation . Clinical signs of benign foot rot are interdigital dermatitis and often, but not always, includes lameness of the affected foot or feet . 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 . 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 .

Diagnosis

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. Scoring is based on the severity of lesions on the interdigital dermis, the junction between the skin and the horn and the horn itself. Cases of benign foot rot tend to score on the lower end of the scale and virulent foot rot cases tend to score on the higher end. Other clinical signs may be present depending on the strain or the severity of the foot rot are loss of appetite, loss of body condition, decrease in wool production , and decreased milk production . Warm and wet conditions are favorable for the spread of foot rot so the presence of these conditions can also help support the diagnosis of foot rot due to d. nodosus as well as promote the spread to other animals in the herd

While not routinely performed, laboratory diagnosis of D. nodosus can be done to determine the virulotype of the infection-causing strain by PCR, gelatin-gel, and elastase assay and can be used to confirm field diagnosis. Identification of extracellular proteases has historically been the basis for the differentiation between the two strains of D. nodosus. Benign strains of D. nodosus have proteases that are thermolabile and virulent strains have proteases that are thermostable and have higher elastase activity. Performance of laboratory testing to diagnose specific strains of D. nodosus by determining the protease thermostability and elastase activity are not routinely performed due to the difficulty of the laboratory procedures that often yield inconsistent results . In addition, the time it takes to perform laboratory-based tests to determine the virulotype of D. nodosus is slow and may not be helpful to effectively treat or isolate the infected animal(s) and to prevent spread to other animals

Known strains

• Dichelobacter nodosus ATCC 25549
• Dichelobacter nodosus VCS1703A

External links

• "Dichelobacter nodosus". nlm.nih.gov. Retrieved 18 August 2016.
• "Genome Project Information (GenomeSeek)". Archived from the original on 2006-10-16. Retrieved 18 August 2016.
• "Animal Health & Production Compendium". cabicompendium.org. Retrieved 18 August 2016.
• Type strain of Dichelobacter nodosus at BacDive - the Bacterial Diversity Metadatabase