Mud Rash in horses – all you need to know

With Ireland’s largely mild and usually wet winters, mud fever is unfortuantely all too prevalent in this country. Given that most horse owners have to face and treat it at some stage, it’s important to know exactly what mud fever is, what causes it and the best way to treat it. So, our equine veterinary expert – Nikki Walshe – has put together this excellent Mud Rash fact sheet. Read on for all you need to know about mud fever…

The Bacteria:

• Dermatophilus congolenis
• Lives dormant in the skin and is activated when the skin is compromised.
• The bacteria germinates within the skin producing hyphae (finger like projections) to invade locally. The scabs allow the bacteria to release spores (zoospores) to perpetuate the infection in the surrounding skin.
• Spreads between horses through fomites (tack, boots etc) or contaminated environments.
• Although it is not proven the bacteria lives in soil, the disease thrives in wet muddy conditions due to penetration of the skin’s defences.

Predisposing factors:

• Standing in wet and muddy fields (often around feed/water troughs and gates)
• Washing legs without thorough drying of the area
• Sweating under rugs or putting on rugs when horses aren’t dry
• Skin irritations from boots or bandages
• Horses with immunosuppression (stress or equine cushings disease)
• White areas of the body, particularly white legs.

Clinical signs:

• Matted areas of hair containing scabs, area of hair loss and raw skin when the scabs are knocked off.
• In more severe cases, infection of the surrounding skin can extend into deeper layers, resulting in a cellulitis which presents as swelling, heat and pain associated with the area.

Treatment:

• Main stay of treatment is removal of the infectious scabs and a dry environment
  • Remove crusted lesions (to stop the cycle of infection)
  • Then clean area with a substance containing chlorhexidine
  • Chlorhexidine wash should be left on for 10-15 minutes before washing off. This washing should be done every other day for the first 5-6 days, then once a week until the lesions are resolved
  • Must dry area completely – applying stable bandages for 1-3 hours post treatment can dry out the area but they must be removed
  • Apply silver sulfadiazine sparingly
• For more severe cases sedation may be needed to allow removal of scabbing
• In the case of cellulitis development, veterinary consultation is necessary and treatment with antibiotics and anti-inflammatories

Mud rash and associated diseases are vexingly common in Ireland. Close monitoring and prevention of predisposing factors are crucial when fighting the ongoing battle. However, some horses are just not designed for poor conditions and thus living inside during wet winters might be a must.

Top tip:

If your horse comes in from work with wet, muddy legs apply stable bandage to dry out the legs and brush off the dirt in 1-2 hours’ time. This prevents re-wetting the area and ensures fully dry skin.

Please note that our veterinary articles are written to give you insights and understanding of common equine veterinary problems and are not intended to take the place of a veterinary examination by your own vet. If in doubt, always call your own vet should your horse require attention. 

Nikki Walshe MVB is a resident vet at Greenmount Equine Hospital, Limerick

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