Footrot causes, symptoms and diagnosis
The footrot bacterium has many strains ranging from benign (mild interdigital dermatitis) to virulent. These can both be present in sheep on the same property and will appear differently.
It is important to know the causes and symptoms of footrot so you can report suspicion of disease. If you see any form of footrot in your flock, no matter where it may be on the disease spectrum, contact us immediately.
Causes
Like many diseases, there are 3 main factors that affect the development, severity, and transmission of footrot between sheep.
Bacteria
Bacteria
Footrot is caused by the bacteria Dichelobacter nodosus (D. nodosus), which can survive in the environment for up to 7 days.
It can live in the foot of a sheep for years and is introduced to a clean flock by infected sheep. In some cases, sheep walking on contaminated ground or pasture can become infected.
Environment
Environment
Warm, moist environmental factors and long grass make sheep susceptible to footrot – these conditions are known as a spread period. The disease develops when there is:
- an average daily temperature of 10°C or higher, lasting for 4 to 5 days
- more than 50 mm rain in the preceding month
- adequate pasture length and density to keep the ground moist over several months.
Footrot is a seasonal disease and usually occurs through spring. The bacteria will die under hot, dry conditions.
Sheep breed
Sheep breed
All breeds of sheep can develop footrot, but some are more resistant than others, such as British breeds.
Merinos, Dorpers and Aussie Whites are susceptible and more severely affected by footrot. Younger sheep are also more likely to develop footrot than older sheep.
Symptoms
Virulent footrot disease shows as:
- chronic and severe lesions
- lameness
- loss of production
- death, in severe cases.
Foot scald caused by D.nodosus is also footrot.
Sheep with footrot showing lameness – photo: WA Department of Primary Industries and Regional Development
Footrot may express as benign lesions:
- early in the disease outbreak – all virulent lesions start as benign
- if only benign strains are present
- when the climate or host are not favourable for expression
- if treatments have been given to reduce the severity of disease.
A scoring scale is used to rate the severity of footrot, ranging from 0 (no signs of infection) to 5 (severe footrot) – see images of each footrot score ().
Diagnosing footrot
Under the right environmental and host conditions, footrot strains can express to produce clinical signs.
When conditions are not ideal, the virulence of the bacterium may be present but is not reflected in the severity of disease and will appear benign.
There are 2 main ways to diagnose footrot in a flock, both requiring inspection of a significant number of sheep.
Clinical diagnosis
Clinical diagnosis
Inspect sheep during a spread period by paring the hooves to reveal the most severely affected individuals in the flock.
The percentage of sheep suffering severe footrot lesions can be used to form a diagnosis of benign or virulent footrot.
Laboratory based diagnosis
Laboratory based diagnosis
The time of year, local climate, and management factors do not always allow for an accurate clinical diagnosis, especially during dry times or in traditionally drier parts of the state. Laboratory testing is the most reliable method.
The SA Footrot Management Program uses a laboratory based 'Elastase test' to assign a flock diagnosis. By submitting samples from multiple infected sheep across the flock, it returns results that indicate how severe a footrot infection may be under ideal development conditions.
Take samples from sheep that are showing clear signs of lameness.
Learn more about diagnosis in the Footrot guide to identification and control in the field (PDF).
When footrot has been confirmed, there are trading requirements and options for treatment. Find out about:
