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What are Pemphigus Foliaceus?

This disorder starts by manufacturing antibodies against its own skin. Hair loss and hives develop because the antibodies are attacking the bonds that hold skin cells together. As it spreads, your horse can develop swelling and blisters in the lower abdomen and legs. No one really knows what causes this condition although some evidence points to insect bite hypersensitivity or even reactions against medications, deworming, or vaccines. Thankfully, this is a rare condition but can be hard to treat when it does occur.

Pemphigus foliaceus is an autoimmune disease that is characterised by primary lesions that often begin on the head before affecting other areas.

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Symptoms of Pemphigus Foliaceus in Horses

  • Difficulty in walking or to lie down because of swelling and lesions 
  • Pus filled blisters
  • Crusty lesions develop and spread 
  • Worsens or reoccurs in the warmer weather
  • Lesions around the coronary band on the hoof
  • Fever 
  • Depression
  • Lethargy 
  • Weight loss and lack of appetite 
  • Hair loss forming patches
  • The skin may be painful 

Types  

There are two main types of Pemphigus Foliaceus

  • Pemphigus foliaceus - Your horse may form blisters which peel off to reveal large areas of hair loss; your horse may be affected by fluid and swelling around the abdomen and the legs
  • Pemphigus vulgaris - This is quite rare and develops burn like blisters on the skin and mucous membranes, namely the throat, eyes, genitals and nose
  • Often mistaken for dermatitis, this condition requires early detection to enable treatment in the early stages

Causes of Pemphigus Foliaceus in Horses

  • It affects your young or older horse, any age
  • No breed has been shown to be more vulnerable than another 
  • No one is really sure of the exact cause as yet – and there are several competing theories
  • Insect bites causing extreme sensitivity is one such theory although unproven 
  • Allergic reactions to medication or worming treatments is another 
  • It is classified by some as an autoimmune disorder 
  • Supplements have also been suggested as a trigger

Diagnosis of Pemphigus Foliaceus in Horses

The primary way to diagnose this condition is by using a punch biopsy of the skin which your veterinarian pathologist will examine and compare to the skin conditions of your horse. As the symptoms are very similar to some other conditions such as insect bite allergies, the pathologist will be looking for changes consistent with the diagnosis. A definite diagnosis can be made by a combination of tests such as direct smears from the blisters and examining the crusted area of the primary and secondary lesions. 

Pathology is the only way to determine that it really is pemphigus foliaceus which is vital as the sooner treatment can start while the condition is in its early stage the better. Once this disease spreads and secondary lesions form, the treatment becomes a longer process and harder to predict the outcome. With no known cause as yet, the condition has no vaccination to prevent it, and changes in management are hard to define without a cause. Again, early treatment is vital so if your horse develops any symptoms of this disease it is essential to call your veterinarian in to advise.

Treatment of Pemphigus Foliaceus in Horses

Treatment using long term glucocorticoids such as prednisolone will form part of the solution, while vitamin E supplementation and omega fatty acids may be used in support. Restricting your horse from direct sunlight and bathing him in cool water may help make him more comfortable. Other causative factors such as your horse’s diet, insect bite allergies and medicated treatments will be assessed to try and find the underlying causes. Treatment is usually long term, or your horse may need to be on medication for life. 

The horses that do recover have a 50% relapse either immediately or even after a few years. Combined with the treatments providing less effect as time moves on, the prognosis becomes quite grim if the condition worsens and fails to respond to treatment. Your younger horse may seem to be affected less severely and recover quicker than an older horse and they may remain in remission after treatment has been stopped. But in general, your horse will become less responsive to treatment each time the condition reoccurs.

Recovery of Pemphigus Foliaceus in Horses

The earlier this condition is diagnosed the better as it responds better to treatment in the early stages than the later stages. The treatment is long and your horse can be on medication for life. Care requires attention to your horse, keeping him comfortable in the stable and out of direct sunlight or away from insects on humid days. Soothing your horse with a cool wash may help while your veterinarian will be able to advise any other actions that you may be able to take to comfort your horse.  Generally, if your horse develops the disease when it is young, for example, less than five years of age, they tend to respond better to treatment and have a higher rate of remission of the disease.