Mud rash – what’s that ?
Richard Knight BVetMed MRCVS on behalf of Peter Fenton Equine Vets
You could be forgiven for forgetting all about Dermatophilus infection ( mud rash and rain scald ) given the sunny, warm summer that we have all experienced this year, however unusual it is. Unfortunately this will, all too soon, be the dark and miserable British winter time, an unenviable mix of wet and cold.
For horse owners this will bring the inevitable, repetitive battle with our winter time woes, one of which is dermatophilosis or infection of the skin with the bacteria Dermatophilus congolensis, commonly referred to as mud rash, mud fever, rain scald and a few other terms. This is a frustrating and, sometimes, seemingly unavoidable infection that affects a large number of horses and ponies whenever the weather is wet and the ground muddy, which can be a large proportion of the year in the UK. This means that it is our responsibility as owners to understand the disease and manage our horses better in order that we do our best to avoid this infection that causes skin damage, swelling of limbs, pain, time out of work and scarring in severe cases.
So, we have already mentioned that this is a bacterial skin infection that is seen commonly in the wetter periods of the year. It predominantly affects the skin of the distal limbs around the pasterns or over the top of the back, especially towards the rump. It is recognised by repeated scabbing of the area that removes a patch of hair when picked off, often referred to as “paint brush” lesions due to the appearance of a group of hairs held together by scab resembling the head of a paint brush. The infection occurs in the wetter weather when water and mud are in constant contact with the skin and this is because it can only survive in an environment that has reduced oxygen, i.e. when the skin is wet then no air can get to the skin surface and the bacteria will reproduce and create an area of infection. This infection then creates the scab which takes over the job of excluding the oxygen from the skin surface and perpetuates the infection.
There are some horses that seem to be affected more easily than others and these commonly include horses with pink skin, reduced protection due to frequent bathing, underlying disease like PPID ( Cushings disease ) or animals that are simply left out continuously in bad weather conditions will inevitably succumb at some point. Obviously some of these things are out of our control like the colour of a horses skin! However, the amount of turnout a horse has is in the direct control of the owner and no one else so can be limited as is necessary; and underlying diseases can be recognised and treated successfully which would greatly improve the overall health of the horse and not just reduce the risk of dermatophilosis. The two most common reasons I see for this infection are inappropriate amounts of turnout in bad weather and horses with PPID that get all kinds of infection much more easily until they are treated. There has to be a recognition by owners that it is turning horses out in bad weather that causes this problem that can be painful, costly and time consuming to treat.
There are also some other diseases that can appear similar to the untrained eye and need very different treatment, commonly these include self trauma caused by itching of horses with mite infestation in the skin of their legs and a less common disease called leucocytoclastic vasculitis which is an immune mediated inflammatory disease of the skin usually initiated by u/v light on bright days and exclusively affecting white skin. These need to be considered in appropriate cases and in suspected mud rash cases that do not improve.
I have tried to discuss the importance of prevention and disease awareness up to now and not mentioned treatment for two reasons, one is that this is a management problem mostly and therefore preventable by changing your routine, it is understandable that people do not want horses stood in but unfortunately our climate is restrictive in that way and if the horse spends a period of time every day when its legs are dry then you greatly reduce the risk. There is always the option to ride or some people may have the luxury of a horse walker. Secondly there are so many different ways that vets will advise you to treat this disease that are all effective that I could go on for a long time discussing them all.
My experience of treating these cases successfully can be split into 2 types of case, mild and advanced. The mild cases are the majority and should be treated quite easily and in a relatively short time. If we consider how this bacteria survives we get the key ways in which we can treat it. It requires the wet conditions and scabs to reduce the oxygen level at the skin surface therefore if we keep the horse dry (stabled) and remove the scabs (with a medium stiffness brush) then the problem will resolve. Some of these cases may require some medicated cream to apply when the scabs have been removed only but certainly, in my experience, do NOT require daily scrubbing with cleaning agents like chlorhexidine or iodine that is actually irritant to open wounds and plastering in any thick creams with wild claims of successful treatment. They can still be exercised by ridden or in hand work but not turned out until the skin has totally healed.
The advanced cases can be more difficult to treat and manage, these are likely to have been left too long before being treated or have been unsuccessfully treated by the horses owner. They can require long courses of medication to manage the infection and pain and can develop complications including lymphangitis and more complicated infections, these cases are commonly left with permanent changes in the limbs with recurrent swelling and scarring common.
The key is that good observation and timely changes in management routine can mean that your horse never gets this disease that is caused by a specific set of conditions on the skin surface that is in the owner’s hands to prevent. This is one of a number of diseases that we can successfully and significantly reduce the number of cases that happen by applying good management and getting early advice from a vet if worried about it.