It’s autumn again, the evenings are dark, and it all means just one thing: it’s time to prepare for another dreaded winter! For horse owners, winter means that the wet, muddy conditions mean that preventative management is heightened. One of the most common yet unpleasant winter ailments is Mud Fever, which thrives in Britain’s typically wet seasons.
What is it?
Mud Fever (Dermatophilosis) is a bacterial skin disease specifically caused by the bacterium Dermatophilus congolensis. Dermatophilis congolensis is a bacterium that loves a nice English downpour. It is found throughout the environment, but to infect horses it has to have moisture, and the skin has to become damaged, either by biting insects or tiny scratches. When it rains, the moisture releases a motile form of the bacteria, which is attracted to areas of damaged skin. Normally, healthy bacteria found on the skin will prevent D. congolensisfrom growing, but rain seems to dilute these good bacterial inhibitors, allowing D. congolensis to multiply unchecked.
Recognising the disease
A history of recent soaked skin and the location of lesions aid diagnosis. Once D. congolensis gets into the skin it rapidly grows in all directions, forming circles of matted hair that make the effected area lumpy and scabby to feel. When you pull on the hairs, they may all come out together and look like the hairs on a paintbrush, leaving an exposed round sore, which can be covered in pus or blood.
Infected areas of skin can be extremely painful, and if the legs are affected, horses can become severely lame. In more chronic cases there can be significant hair loss, and the sores can develop into thick crusts that are very difficult to remove. Unlike some other skin conditions, Dermatophilosis is rarely itchy.
A definitive diagnosis can only be made by looking at the pus and identifying D. congolensis through a microscope. Ideally your vet should make this definitive diagnosis before treatment begins, but sometimes the history and clinical signs will be enough for specific treatment to be recommended.
Fortunately, while Dermatophilosis is extremely common, it is also well understood and once properly diagnosed it responds quite predictably to treatment. The most important rule to remember is not to apply a thick layer of miracle-cure-cream straight onto the effected area and expect anything but failure. The bacteria will hide beneath any intact crusts, multiplying happily in the moist, warm conditions.
First you must remove any loose crusts to expose the underlying sores. The more persistent and difficult crusts should be gently massaged off with a weak antiseptic solution such as Hibiscrub, Malaseb shampoo or Povidine iodine. This process can take some time and may need to be repeated daily for several days before all of the scabs can be removed.
Sometimes it will be impossible to remove the scabs without first sedating your horse. Your veterinary surgeon should be called if sedation is required, so that all of the scabs can be removed safely. Any scabs that are removed will remain infectious for a long period of time, so they must be disposed of carefully to prevent horses becoming re-infected at a later date.
Once the underlying skin has been exposed and cleaned, it is essential that it is thoroughly dried, and then kept dry. Only then should any topical treatment be sparingly applied and rubbed well in.
If the effected skin can be kept dry, most cases of mud fever will resolve. However, this is obviously impossible in this country over the winter. Therefore, the cleaning and drying process will need to be repeated each time the effected area gets wet again.
In more severe infections, topical treatments may not be sufficient, and your vet may prescribe systemic antibiotics and anti-inflammatory drugs to get things under control. The most effective antibiotics for this condition are usually penicillin or trimethoprim sulfadiazine.
Once the skin has healed, preventing re-infection remains very important. Horses do not develop immunity to the bacteria and can get re-infected as soon as moist conditions return. It is extremely difficult to get the skin of wet horses dry, especially if they have thick feathers. Hosing, toweling and a deep dry bed overnight will help, but sometimes prevention can only be achieved if the feathers are gently clipped off to allow drying of the underlying skin.
Above all else, remember that mud fever can become very serious, and could put your horse out of work for long periods. Keep working at the cleaning and drying, but if you are concerned that the condition is not improving, get your vet out sooner rather than later. Then you’ll be able to warm your own feet by the fire without worrying about the horses outside.