.. is caused by Dermatophilous congolensis - a gram positive, facultative anaerobic actinomycete (easiest to think of it as a higher bacteria - not quite a fungus). It is part of the normal flora on horse skin, and does not cause problems until the skin is damaged and moisture is present. Moisture then causes the bacteria to release motile zoospores that invade damaged skin and initiates the characteristic skin lesions. Treatment guidelines:
1) many cases spontaneously cure if the area can be kept dry
2) keeping the skin dry is very important
3) crust removal and topical therapy is very useful. I`ve had good success with nitrofurazone ointment alone or in combination with corticosteroids for swollen, painful lesions. On legs, it speeds up recovery to keep the affected areas covered to provide a continuous contact of the ointment and to keep the lesions dry.
4) systemic treatment may be necessary in severe cases. Since this is a higher bacteria, it will respond to antibiotics. Penicillin is recommended in most texts, but for those who don`t like injecting their horses, in my clinical experience, Trimethoprim/sulfas are equally effective.
Some horses are far more prone to flare ups than others. One can keep lubricating things on the pasterns to prevent chapping and cracking of the skin from wet pastures - vaseline, mineral oil, etc work well. Avoid washing muddly legs - brush dry instead.
Trisha Dowling, DVM, MS, Dip ACVIM,ACVCP
Associate Professor, Veterinary Clinical Pharmacology
Western College of Veterinary Medicine
comments from Lynn Crespo
We have 2 horses that are highly susceptible to rainrot and both have developed severe cases over the last year because of the incredible rain we have here. At some point, both required antibiotics and corticosteroids for the infection and inflammation. Since the rain persists and I am adamantly opposed to long term antibiotic and steroid therapy I put on my thinking cap, asked a zillion more questions and have found a very simple, but effective treatment that has worked wonders for us.
Baby oil and Vinegar (half and half). After cleaning and thoroughly drying the area I spray the solution and work it into the area. The baby oil lubricates the skin to prevent cracking and flaking and the vinegar, which is acidic, changes the pH of the skin to make it inhospitable for the bacteria to grow. Acutally, vinegar is an excellent antiseptic. It is commonly used to sterilize respiratory equipment used in the home. We use it daily on my son`s nebulizer. It is a little smelly, but it cleared up the rainrot in 4 days.
I now apply it every night on our 2 problem horses, because it can rain at any given minute. The oil also adds a protective barrier for the skin and the water just beads up and runs off!
L. M. Crespo, Ph.D.
Associate Professor and Chair
Department of Pharmacology