Mud fever: Recognise, treat and prevent it

At this time of year, particularly with such prolonged wet weather, horse owners should be on the lookout for signs of mud fever, a difficult and painful disease affecting horses’ lower legs.

MUD fever is very topical at the moment, explains equine vet and author of The Veterinary Care of the Horse, Sue Devereux. “We’re having unusually wet weather conditions and it is a disease that horses are susceptible to when their legs are wet and muddy for prolonged periods.”

In this examination of mud fever, reproduced from her recently updated publication, Sue outlines the clinical signs of mud fever, the potential causes and different approaches to treatment and prevention.

Mud fever is a common condition that affects horses living or working in wet, muddy conditions. The skin over the pasterns and heels becomes infected, resulting in scabby or exudative lesions which can be very painful.

Sometimes the infection extends to the skin further up the legs.

White limbs are particularly susceptible. It occurs mainly in the winter months.

In fact, mud fever is not a single disease but a collection of clinical signs associated with a number of different causes. To manage the condition successfully, one needs to be able to recognise the signs and identify their underlying cause. Although very common, it appears in various forms and is not limited to horses that are literally paddling knee-deep in mud.

Clinical signs

Mud fever can range from a mild skin irritation to very painful, infected sores. The disease can actually affect the whole body and is given different names depending on the part of the horse affected.

When it occurs along the backs of horses that are kept outside without rugs, it is known as rain scald or rain rash.

Mud fever is the term used to describe the condition when it involves the lower limbs, most commonly the back of the pastern and the heels, where it is seen as crusty scabs.

The inflamed skin may discharge serum, causing the hair to matt, giving the coat a rough, ungroomed appearance.

With severe cases, the skin at the back of the pastern may split open, producing deep horizontal cracks, commonly called cracked heels. Infection can enter these areas of damaged skin, resulting in a hot, swollen and painful leg and cause severe lameness. In the summer months, a less severe but equally persistent form of the disease occurs. Firmly adherent scabs are found in the pastern and heel regions.

Causes

There are many factors which can be divided into the predisposing and infectious causes.

Predisposing causes include:

  • The horse’s own genetic makeup. Any horse with white hair on the lower limbs and/or a long shaggy coat around the lower limbs (known as feathers) may be prone to mud fever.
  • Environmental conditions. Anything that irritates, softens or breaks the skin so that infection can enter, makes mud fever more likely to develop.
  • Physical and chemical irritants which damage the skin. These include contact allergies, insect bites and injury (rubs) from dirty overreach or brushing boots.
  • Other infections, eg: ringworm and chorioptic mange mites, can damage the skin and allow secondary infection to occur. In these cases, it is important that the underlying cause is identified, as neither the mites nor the fungus will be sensitive to antibiotics. This is one of the reasons why antibiotics do not always cure the condition.

Infectious causes include:

  • Certain infections are able to invade the skin when it is compromised by the factors discussed above. These include bacteria such as Dermatophilus congolensis and Staphylococcus spp.

Diagnosis

Diagnosis of the disease is usually straightforward. The diagnosis is made on:

  • The clinical signs.
  • Identification of the microorganisms under the microscope and occasionally culture of the microorganisms in the laboratory.

Identifying the factors that caused the irritation is not always easy. While muddy paddocks are often the cause, skin trauma from working in fields of stubble or irritation from harvest mites can be contributory factors.

Treatment

There are many treatments for mud fever. It has to be remembered that with any condition for which there are a large number of possible treatments, it is often because nothing is a guaranteed success.

Changing the environment

The first step is to remove the horse from the cause, eg: the wet and the mud. Undoubtedly, there are cases where the only hope of a cure is to change the environment and this usually means stabling. However, if the horse is kept in all the time and not exercised, the legs will tend to swell.

Walking exercise in hand, several times a day, is helpful initially. Once any lameness has been resolved, working on a dry surface which does not scratch the legs further will help the circulation and encourage healing. Roadwork is often best for these horses.

Stable management

The horse should be stabled with a clean, dry bed. Dirty bedding will increase the risk of infection. Straw may be abrasive to the damaged skin and shavings are best avoided as they adhere to the wounds. Cardboard or paper bedding are suitable and protective bandages can be useful.

Treating the lesions

The affected area should be carefully clipped, taking care not to traumatise the skin further. This may be done with clippers or a good pair of curved scissors.

Then use an antiseptic wash such as chlorhexidine (Hibiscrub®) to remove as many of the unhealthy, crusty scabs as possible. You may need your vet to help by sedating the horse and giving painkillers.

Next, gently rinse and then blot the skin dry with clean, absorbent tissue. Rubbing it with a towel will be painful for the horse and could cause further damage to the skin. A hairdryer with a circuit breaker may be used, taking care not to burn the delicate skin.

Topical Treatments

There are numerous topical treatments that can be used as an emollient to maintain hydration of the skin. These include soothing ointments, gels and creams, some of which contain antibiotics.

Recent additions to the range of treatments include an ointment containing an antibiotic and silver, and also a dressing impregnated with silver which has been shown to have strong antibacterial properties.

Early trials with these products look promising. Your vet will recommend the most suitable for your horse.

Dressings

In the early stages, open wounds resulting from the removal of the scabs should be covered with a non-stick dressing applied under cotton wool or gamgee, held in place with bandages. This keeps the lower limb warm, clean and dry; it may help to leave the legs unbandaged for at least an hour a day to allow the area to ‘breathe’.

The horse may be stood in an empty box for this short period of time. Treatment of the sore areas needs to be repeated daily until the condition is under control.

Antibiotics

Severe cases with obvious infection often need a long course of antibiotics. These may need to be continued for 7–10 days after the soreness has settled down. Your vet may also prescribe non-steroidal anti-inflammatory drugs such as phenylbutazone to reduce the pain and swelling.

Aftercare

Once the infection has resolved and the lesions have dried up, the bandages may be removed. The legs should be protected from moisture, mud, abrasions and flies as the newly-healed skin may be tender and susceptible to injury or reinfection.

Prognosis

Mud fever is a difficult condition to treat and it may take many weeks for the lesions to heal completely. If the case is straightforward and the causes are treated or removed, then the disease will usually resolve quickly. However, if the condition has been ongoing for some time, the skin itself will have developed chronic changes which are harder to treat.

Prevention

Prevention and early recognition and treatment are the keys to success in the management of mud fever. Susceptible horses should be carefully inspected each day. There are different schools of thought on whether muddy legs should be left to dry or hosed off when the horse is brought in.

High pressure hosing and use of a coarse brush on muddy skin should be avoided as it could damage the skin and introduce infection.

Some horse owners find that application of barrier creams – such as zinc and castor oil – help prevent infection in susceptible horses. The legs must be clean and dry when these are applied or moisture will be sealed in, creating an environment where the harmful bacteria thrive.

Protective boots and bandages may be used during turnout. These can be very helpful as long as mud does not work its way underneath and rub the horse’s skin. Bandages can be applied when the horse is stabled, to help dry the lower limbs.

Hygiene measures

Dermatophilus congolensis can survive in crusts of scab and exudate for up to three-and-a-half years. Chronically infected animals are a source of soil contamination.

  • The infection can be spread on shared grooming kits and clippers. These should be cleaned and sterilised after use on an infected animal.
  • Scabs that have been removed from infected legs should be disposed of carefully. The bedding should be removed and stable disinfected, eg: with Virkon®, after the horse has recovered.

In conclusion, mud fever is one of those conditions that can be very difficult to control. Unfortunately many horses will have a bout of mud fever at some time in their lives, despite all efforts at prevention.

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