Mud fever is not a single disease but can be seen in differing forms. It occurs especially in warm, wet weather, and is associated with a number of causes. It is certainly not limited to horses that are paddling knee deep in mud! Mud fever can range from a mild skin irritation to very painful infected sores, and can in some cases cause significant swelling with severe lameness. The condition affects the lower limb, most commonly the back of the pastern. It starts off as matted hair with dry crusts, caused by the inflamed skin weeping. When the same condition occurs on the upper body it is referred to as “rain scald”.
The bacterium Dermatophilus congolensis causes mud fever and under normal circumstances this bacterium lives in soil as spores and can survive from year to year. These spores become activated by wet weather and this is why we see the disease when the ground is wet.
This bacterium cannot invade healthy skin. In the winter the rain and mud soften the skin, constant wetting and drying of the legs causes the skin in this area to chap, and then the bacteria can enter. Indeed anything which breaks the skin such as a small cut or wound can allow the bacteria to invade. For this reason muddy conditions are not always necessary for mud fever to occur.
Some horses seem more prone than others and this is because their skin is a less efficient barrier to infection. For example, horses with white and/or hairless pasterns appear to suffer more and horses with very hairy legs may suffer less (as their skin is a bit more protected). If a horse is suffering from another form of infection such as chorioptic mange or ringworm, the skin can become damaged and this allows a secondary infection to occur. It is important then to identify and treat the primary cause as neither mange nor ringworm will be cured by using antibiotics. The picture above shows a typical case of mud fever.
The diagnosis of mud fever is usually straight forward and can be made by identifying the matted hair, crusty scabs and exudate on a horse’s leg. The treatment of this condition is unfortunately not always as simple! The importance of regular inspection of the horse’s legs to catch the condition early cannot be stressed enough, and as always, prevention is much better than cure.
The treatment of mud fever begins with thorough washing of the affected limb(s) with an antibacterial shampoo to remove the crusts and exudate (as these harbour the infection). Either dilute Hibiscrub (1:40 dilutions) or Malaseb shampoo are ideal. The shampoo should be worked into a lather and left on for five minutes before rinsing off with warm water. The leg must then be DRIED thoroughly with a clean towel or cool hair drier (with circuit breaker). Once dry, the hair must be clipped away around the lesion (this may require sedation) and an antibiotic ointment applied. It is important to dispose of the scabs properly as they can remain infectious for up to 42 months! The scabs may form again quickly so initially the legs must be washed daily.
If the bacteria penetrate deep into the skin, the leg may become swollen and a course of antibiotics may possibly be required. In this situation the horse must be seen and treated by a vet. It is necessary to stable those who are affected badly, to prevent the skin from any further wetting or exposure to mud until the skin surface is healed. In fact the infection is self-limiting in dry conditions. We do not recommend covering the limbs of these horses as the warm and moist environment achieved by bandaging can cause the infection to worsen, and possibly force the infection further up the limb. Once the infection has been eradicated it is imperative to keep on protecting the area until the new skin and hair has formed.
Once a horse has suffered with mud fever it is not unusual for them to have repeated attacks, so obviously it would be better if the horse did not get the infection in the first place.
Therefore, some or all of the following steps can be taken to minimise its occurrence:
- To prevent the skin from chapping it is better not to hose down muddy legs but allow the mud to dry and then brush it off. If this is not a practical option, then it is very important that the legs are dried thoroughly after washing
- Application of a barrier cream to DRY and CLEAN legs prior to exercise or turnout will help to prevent the skin coming into contact with the bacteria. There are numerous preparations available, but ones with a soothing emollient and oily base are ideal.
- If bandaging prior to exercise, ensure the legs are clean and dry beforehand and removed immediately afterwards to avoid any grit or coarse material traumatising the skin surface
- Ensure that bedding is clean, dry and non irritant to the lower limbs
- Consider the use of nutritional supplements to promote healthy skin.
- Wherever possible avoid horses standing in poached paddocks and gateways
- But most importantly of all, inspect your horse’s legs daily to spot any early signs of infection and hopefully minimise the risk of a miserable and lengthy period of recovery for you both.