could a sweat rash on my horse cause, flat scabs about as big as 10 pence with pus between them and my horse’s?
It is more likely that the sweat has led to compromise of the skin integrity which allowed the development of an infection by the anaerobic bacteria causing rain rot (dermatophilus congolensis). The bacteria live in the horse’s skin and are opportunistic. When conditions allow the skin to be compromised, the bacteria become active and begin to colonize and you see the lesions which contain pus and form scabs. Because the bacteria are anaerobic (thrive without oxygen), you do not want to apply any oils or other petroleum based products, which deprive the skin of oxygen and allow the bacteria to multiply. You also need to get the scabs removed to expose the bacteria to oxygen.
Severe cases can require systemic antibiotic treatment, but if the case is relatively mild and superficial, topical treatment can eradicate it.
It is important to be very gentle in treating it. You don’t want to drive the infection into deeper tissues, or spread it by vigorous grooming or rubbing.
I recommend soaking the scabs in 0.9% (isotonic) saline solution which you can buy at any drugstore. This will soften the scabs so they can be gently removed. I use cotton pads soaked in saline to cleanse the sores beneath the scabs and remove all pus and debris. You can also just squirt the saline on to flush the lesions. Then pat them thoroughly dry, leaving them exposed to air.
Often that is all you need to do. Once the scabs are removed, the salt in the saline will dehydrate and kill most of the remaining bacteria. Exposure to air will kill the rest, since anaerobic bacteria only thrive in dark, moist environments with no oxygen supply. Because it is balanced with body fluids (isotonic), the saline will not damage the healthy tissue, which is important to maintain skin integrity for healing and fighting spread of infection. Other chemicals often used, such as iodine preparations do damage healthy cells and can prolong the infection as a result.
Using this treatment can mean the difference between clearing the infection within a few days versus it taking weeks with other methods.
If there are vectors present, such as flies and mosquitoes which could reinfect the open sores, you can apply a thin layer of an ointment called EMT which is a collagen gel that adheres very well, maintains skin integrity, and won’t encourage the anaerobes to thrive the way other ointments can. Just be sure all debris is removed and the lesions are completely dry before you apply the EMT. Using a thin layer will allow oxygen to the skin, but prevent infection by vectors.
This treatment is safe to use even if this isn’t rain rot, and if it is rain rot, it is the best, fastest way to eradicate this infection that I’ve seen in my decades with horses, and having seen everything under the sun tried. It is also inexpensive, and not messy or difficult to accomplish.
So, you need cotton pads or gauze, 0.9% saline solution, and if you need an ointment, then you can get EMT at any tractor or farm supply store, or online. I also recommend using EMT on all open wounds, after flushing with sterile isotonic saline, so these are good to have on hand anyway.
If this treatment doesn’t get the infection under control within a couple days, then it may indicate that the infection has invaded deeper tissues and will require systemic antibiotic treatment to get it under control. Again, if you are gentle in treating this, you are less likely to drive the infection deeper or to spread it over a larger area.
Add….regarding sulfur, as is found in preparations like MTG, it is not a bacteriocidal against these strains, meaning it doesn’t kill the bacteria. It is a bacteriostatic, which means it can inhibit the growth or spread of some strains of bacteria, but it doesn’t kill them. There are bacteriocidal antibiotics that effectively kill d. congolensis, but they are not applied topically. These antibiotics are best administered by injection, and act systemically.
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