Rain Rot

  (Photo credit: mseda.org)

As we leave behind one of the wettest years on record for NC, chances are you have at least heard the term rain rot over the last few months.  Rain rot, aka dermatophilosis, is a skin condition that affects horses housed primarily outside.  The condition is often mistaken for a fungal infection but is actually caused by the bacteria, Dermatophilus congolensis.  The bacteria lives dormant on the skin of horses and under normal conditions is benign, but when the skin becomes rain soaked or broken by either trauma or insect bites, it is more likely to develop into the condition.  A heavy winter hair coat is more likely to hold moisture close to the skin, causing anaerobic (lacking oxygen) conditions and exacerbating the condition.  

Rain rot can usually be diagnosed by visual inspection.  The hair coat will be in matted tufts from neck to hindquarters with lesions on the skin underneath.  Sometimes the legs will be affected as well.  If not treated promptly, the lesions will grow and create scabs with yellow-green pus under them when removed.  Any hair attached to the scabs may come off as well.

Treatment starts with removing the crusty scabs to expose the infected skin to oxygen.  Scab removal is usually done by bathing the affected area in some type of antimicrobial soap (Betadine, Chlorhexidine, etc.) and gently removing the scabs with a brush or curry comb.  In severe cases, antibiotic treatment may be required.  After the skin is cleaned and scabs removed, it is important to keep the skin dry by either housing the horse in a barn, or if that is not possible putting on a weather proof blanket, although this method is not preferred because it limits the amount of oxygen reaching the skin.  

Rain rot is highly contagious so good sanitary practices should be used if you have an infected horse on your farm.  It can be transferred through brushes, tack, and even by insects so cleaning equipment and tools and isolating the infected horse is important in keeping this infection from spreading.  You should also never share blankets between an animal that you suspect is infected with other animals.  Wash hands thoroughly after handling the infected horse.

Mild to moderate cases of rain rot should clear on their own, but all cases should be treated to prevent the infection from worsening or from spreading to other horses.  If you suspect your horse has a case of rain rot and antimicrobial treatment is not effective, contact your veterinarian.