What's the Itch on Rain Rot?

Rain Rot

The bane of many people's existence in the late fall or late wet spring in my area, it is known by a few different names such as rain scald or even greasy heel.

But what is it? 

I see people offering up advice continuously on how to approach and treat rain rot and while there are multiple ways to approach a problem, sometimes a little education and understanding is a good foundation upon which to stand.

Rain rot is caused by a bacteria called dermatophilus congolensis.  It is a gram positive bacteria.  But more simply, it often exists already on the skin of our horses.

But then why do horses have an issue when chronically wet, especially with a long winter coat?  This bacteria is a faculative anaerobe, which means it can exist in the presence of oxygen, but prefers carbon dioxide.  Most bacteria prefer a dark, moist area to reproduce.  It already exists in the skin (epidermis) of the horse.  When the horse's coat is wet for long periods of time, it can be drawn upwards through the epidermis externally to spread and begin to reproduce rapidly in a dense carbon dioxide pocket just on the outside of the horse's coat at the bottom of the long winter fur. 

Know those nasty little scabs?  Simplistically, that's a little pocket of the nasty bacteria.

So how do we approach the itch and why should we bother? 

Quite simply, secondary infections are a possibility for the horse.  When one bacteria begins to rapidly proliferate and stress an animal, another native bug like Staph or Strep (yep, they exist naturally on the skin as well) can overgrow and cause a much more serious infection.  Number two, it's painful to the horse and the hair loss is unsightly.  It can be contagious to other horses and animal species, including humans, so be warned.

So how can we treat this? 

The easiest way is something that will kill the offending bacteria.  But realize that the bacteria is often in tight little pockets and those icky scabs.  That's why the first step is to gently remove the scabs.  If possible, the long fur should be aerated too, ie if clipping is possible.  Keep the horse out of prolonged moist conditions.  Then treat the affected area with some specific method to kill it.  Some people use Listerine or other mouthwashes which can contain antiseptic or antibacterial agents, or just alcohol.  This can work too.

But from a microbiological standpoint, scrubbing the horse with betadine or chlorhexidine will also work and then you know which antiseptic you are treating your horse with.  A benefit of betadine/chlorhexidine is that they don't induce excess scar formation/delay healing time that some antiseptic agents do like hydrogen peroxide.  

If a horse is badly infected, then a veterinarian may need to look at treating a horse with antibiotics, especially if there is a secondary bacterial infection or it is on a joint like the pastern.  Good thing is that gram positive bacteria (like dermatophilus!) have a thinner outer wall and are susceptible to penicillin (unless resistant which of course is a whole other idea).  :)  So, if you are concerned that the horse's case of rainrot isn't healing, despite treatment, then there are other options.

So what do you think?  What do you use to treat rain rot?