Mud fever is a group of diseases of horses causing irritation and dermatitis in the lower limbs of horses. Often caused by a mixture of bacteria, typically Dermatophilus congolensis, and Staphylococcus spp, mud fever can also be caused by fungal organisms (dermatophytes). Photosensitization, chorioptic mange mites, contact dermatitis and other conditions also contribute to some cases. This condition is often called scratches or dew poisoning, but is also known as pastern dermatitis, grease heel, or greasy heel.
Mud fever affects most horses and ponies during winter and early spring. Resulting in painful sores and scabs, which in severe cases can make a horse lame. Mud fever most commonly affects the pastern and heel area but can also affect the upper leg, the belly, and in some cases the neck area (also known as Rain Scald). Non-pigmented skin tends to be more severely affected.
Mud fever is caused by an infection of the skin by bacteria, including Dermatophilus congolensis, and often Staphylococcus spp. Dermatophytes (fungal organisms) can also contribute, as can chorioptic mange mites. Photosensitivity may contribute in certain cases. Rarely, vasculitis can cause continued inflammation.
Under normal circumstances the skin acts as a protective barrier, preventing microorganisms from entering the horse's system and doing any damage. However, the integrity of the epidermis can become compromised through the abrasion of soil grit on cold, wet skin. The continual wetting of the skin causes a breakdown of the protective barrier of the epidermis, allowing the bacterium to enter and cause infection.
Shared boots, wraps, grooming supplies, and horse-handler's hands can all serve as fomites, carrying the causative organism(s) from one individual to another. For this reason, mud fever should be considered a contagious disease, and general hygiene steps should be taken to limit cross-contamination.
Horses and ponies standing for hours in muddy, wet paddocks and at gates are a common sight during the winter months and early spring. It is in these conditions that mud fever thrives. Generally, those horses and ponies with white socks are more prone to the condition, although Mud Fever will affect horses of all breeds, ages and colours.
As with any bacterial infection, Mud Fever can become a very serious condition very quickly. The legs can become swollen and sore and open sores can become quickly infected. Often, such is the level of damage to the skin that these open sores can become very difficult to heal and can result in proud flesh, permanent hair loss and in severe cases the need for skin grafts.
In draft horses, particularly Clydesdales, Shires, and Belgians, a similar-appearing, but more serious condition occurs called chronic progressive lymphedema. This condition appears to be genetically-linked, starting early in life and progressing, causing thickening, fibrosis, and predisposing to secondary infections. This disease can progress enough to require euthanasia.
Preventative action should be taken as soon as the paddocks start to become wet and muddy. Rotation of paddocks keeps horses from having to stand in wet, muddy ground. Electric fencing may also prevent horses from standing for long periods in the deep mud that collects in high traffic areas.
Washing the infected area with an antiseptic solution is part of the treatment for mud fever. However, washing a horse's legs repeatedly can remove the natural oils in the skin and may allow the condition to become established. The legs should be dried thoroughly after washing with antibacterial shampoo using paper towels,
There are many products available to help protect the skin from the constant wet by forming a barrier between the mud and the leg. However, barrier creams have the disadvantage that the horse's legs are still covered in mud when they come in from the field. Alternatively, some form of covering for the leg may be used such as Anti mud fever boots.
Keeping the horse out of the wet and mud is the first step in treatment of mud fever. Initial treatment also consists of clipping of the hair away from the infected area and use of an anti-bacterial lotion on the scabs to soften them and gently remove them. When the scabs are removed, the skin is kept clean and dry. A Veterinary Surgeon is consulted for further treatment.