The term “rain rot” sounds like frostbite or some other topical condition caused by exposure to inclement weather, but it is actually a bacterial infection that affects horses and other animals that are subject to prolonged rain and moisture. To those who are not familiar with rain rot, its appearance may suggest a fungal infestation or a parasite invasion, but the reality of this dermatological condition, which is formally known as dermatophilosis, is that it is caused by bacterial colonization, specifically by the congolensis pathogenic microorganism.
You may have heard of rain rot being called rain scald or mud fever. Some veterinarians call it cutaneous streptothricosis, which is a more accurate description since the bacterium in this case is gram-positive. Severe rain rot can be a dangerous condition for affected horses because it can cause an infectious chain reaction that the equine immune system will have a hard time trying to contain. The good news for horse owners is that rain rot can be easily treated as long as it does not grow into a systemic infection; moreover, rain rot is also preventable in many cases.
Before we get into the treatment and prevention of rain rot, it helps to understand how it occurs and develops.
Dermatophilus congolensis
This microorganism is one of many that live on the skin of horses. There are a few characteristics that sets it apart from other equine bacteria, including:
- Polymorphism
- Gram-positive stain
- Aerobic nature
- Filamentous appearance
In and of itself, the moderate presence of congolensis is not a problem for horses or other animals. The problem occurs when the bacteria finds a nutritional source and starts to colonize the dermis. Congolensis will feed on spores, chemical compounds, and fungus that proliferate when the skin is warm and wet. A perspiring horse with oily skin may temporarily provide nutrition to congolensis, but this situation goes away as soon the horse skin naturally dries out, ideally with the natural disinfectant we know as sunlight.
The reason congolensis infections are called rain rot and rain scald is because they often occur when horses are constantly getting wet under the rain and without an opportunity to properly dry out. In reality, any situation that makes horse skin warm and humid could result in dermatophilosis, and this would include perspiration as well as excessive biting from insects.
When dermatophilosis goes into systemic mode, the equine immune system will kick into high gear, and this can sometimes result in elevated core temperatures, thus explaining why this infection is sometimes called “mud fever.” We know that horses and other animals such as pigs will often find mud to be an irresistible playpen, but we should not think that dermatophilosis results from pathogens that horses picked up from their mud baths; what is actually happening is that congolensis bacteria are being fed by the conditions created by the mud.
It is safe to assume that keeping horses dry is the best method to avoid rain rot, and we will discuss this after we describe the condition and its treatments.
Where And How Rain Rot Occurs
The coat is not directly affected by rain rot even though this is where congolensis usually resides. Once bacteria start feeding, they will grow filamentous and reach the top layer of the skin in order to form colonies. The pores will allow bacteria to penetrate the top layer of the skin, and this is when horses start feeling pain because the nerve endings are right there to complain about the inflammation and lesions.
With the skin being the largest organ of equine species, it stands to reason that rain rot can occur just about anywhere. We tend to see rain rot form down the neck, back, and all along the dorsal section towards the hindquarters. Some horse owners have noticed rain scald form on just one side because the animals are only exposed to the sun on the opposite side in their barns.
As previously mentioned, a wet horse that does not get to dry under sunlight will be a prime target for rain rot, but there are other ways for congolensis to colonize and create a dangerous health condition. Just like primates, canines, and felines, equines have their own version of the herpes virus; if a horse goes through a serious herpes episode that causes fever and perspiration, there is a strong chance of rain rot developing. The same can be said about the equine virus that causes encephalitis, and which is often transmitted via insect bites. In other words, rain rot can be a primary or secondary condition.
It is important to note that congolensis bacteria can colonize the top skin layer and work their way inside through the pores. The resulting scabs are proof of the dermal degradation, and the fact that lumps of hair can come off with the scabs lets you know that bacteria colonies have penetrated the skin.
Treatment of Rain Rot
If the horse does not show symptoms of systemic infection, you should be able to provide care on your own and without a visit from the veterinarian. You can detect rain rot when grooming the horse; if you see spots where the coat is tufted and does not follow the direction of the other hair strands, take a look at the skin and around the pores to check for signs of redness and inflammation. Scabs may have already formed, and this is a dead giveaway along with lesions that are tender to the touch.
Taking the temperature of the horse and checking for symptoms of fever should be your next step. While you can certainly treat rain rot as a primary or secondary condition, you do not want to leave the primary illness unchecked. Rain rot along with fever and erratic behavior could be a prelude to encephalitis, particularly if you know that the horse has been staying dry.
Most cases of rain rot can be treated in four days. Let’s go through each one:
- Day One: Identify the infected spots and spray them down with Banixx Wound and Hoof Care. You will want to soak the affected areas for now. The goal for the first day of treatment is to introduce an antiseptic solution that can kill bacteria while lubricating the scabs at the same time.
- Day Two: You can now use eZall Anti-Allergen Shampoo and a gentle brush on the scabs and inflamed areas. There is no need to rinse off on this day. Please resist the urge to pick off the scabs; you will likely see some of them come off on their own, but you do not want to remove them at this time.
- Day Three: A second application of the aforementioned medicated shampoo should be completed on this day, and you can now use the brush or a comb to remove scabs. The robust immune systems of horses will start healing the skin soon after the first day of treatment, but the affected areas may still be sore, which means that you should be gentle when pulling off scabs.
- Day Four: Take a look at the infected spots and look for signs of the inflammation going away and hair growing back. If this is the case, you can reapply Banixx Wound and Hoof Care and let the healing process take care of the rest. If scabs remain, you should continue the shampooing sessions until they are gone and before spraying with Banixx.
Rain Rot Prevention
All horses enjoy sunlight; let them get as much of this powerful antiseptic as they want, particularly after a scrub-down, rain, or trail ride on hot days. This is all it takes to prevent primary rot, but you should not forget that rain scald can also be indicative of more serious issues. Keeping your horse healthy can go a long way in preventing secondary rain rot infections. If you suspect rain rot on your horse, make sure to seek veterinary care before doing anything else.