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Rain Rot / Rain Scald
PREPARED BY: Cheryl Sutor 
What is rain rot?
Rain rot is one of the most common skin infections seen in horses. It is also referred to as "rain scald" or "streptothricosis". The organism that causes rain rot appears and multiplies in warm, damp conditions where high temperature and high humidity are present. This condition is not life-threatening, so don't worry. However, while the horse has rain rot, any equipment that may rub and irritate the infected skin (such as saddles and leg wraps) should be eliminated.
What causes rain rot?
The organism dermatophilus congolensis causes rain rot. dermatophilus congolensis is not a fungus. It is an actinomycetes, which behaves like both bacteria and fungi. Most people believe that the organism is present in soil, however, this has not been proven. The organism is carried on the horse, who has it in his skin. A horse who has this organism in his skin may or may not be affected.
What does rain rot look like?
Rain rot can appear as large crust-like scabs, or small 1/4 inch matted tufts of hair. There is usually dozens of tiny scabs that have embedded hair and can be easily scraped off. Underneath the scabs, the skin is usually (but not always) pink with puss when the scabs are first removed, then it becomes gray and dry as it heals. It is usually hard to differentiate rain rot from other similar skin conditions, so if you are unsure, call your veterinarian.
In the early stages, you will be able to feel small lumps on the horses' skin or hair by running your hand over your horse's coat.
In what region is rain rot most common?
Rain rot can be present in any horse around the world, but is most common in South Florida. In South Florida, the increased humidity and high temperatures combine with the prolonged rainfall to create the perfect environment for the organism to live.
What conditions are usually present?
1. The animal has to be infected with the organism. A horse can become infected by shared saddle blankets, leg wraps and brushes with other infected horses.
2. There has to be extreme moisture present. Horses with thick coats are more likely to keep the moisture close to their skin.
3. The skin has to be damaged (by a cut or scrape), for the organism to be able to enter the epidermis.
4. Also, poor stable management, damp stalls, poor ventilation and infected barns.
Will rain rot go away on its own?
It sometimes does. What I mean is that some horses will naturally get rid of the organism as they shed out their winter hair coat. However, it is not advisable to let the condition persist, you should not wait to see if it will go away...start treating it now, before it gets any worse!
Does rain rot lead to any other conditions?
Since the organism needs a warm, moist environment, it is likely that a secondary bacterial infection may become present. The most common secondary bacterial infections known are staphylococcus (staph), and streptococcus (strep). This is why it is very important to treat rain rot immediately, since any secondary bacterial infection may be even more resistant and difficult to treat.
How does rain rot spread?
The organism, dermatophilus congolensis, can be spread through sharing of equipment between horses. This includes saddle pads, blankets, leg wraps, brushes, halters, etc. It is extremely difficult to prevent the spread of rain rot, since a horse can pass it to another horse by simply rubbing it's skin on any object that the other horse may touch. The best prevention for rain rot is to use a disinfectant on any equipment shared between horses after each use.
When treating this condition, you must keep all equipment used on the horse disinfected, to be able to keep the organism from coming back. A good solution is 2 tablespoons to 1 gallon of water of Chlorox. Do not use this solution on your horse, only on the equipment!
Where does rain rot appear?
Usually on the horse's back and rump, along with the back of the fetlock and front of the cannon bone. It may also appear on the tips of the horse's ears and around the eyes and muzzle. When rain rot appears on the lower limbs (behind the fetlock), it is most commonly referred to as "dew poisoning".
Are the scabs painful to the horse?
No, the scabs do not hurt the horse. The scabs have not been associated with an "itchy" feeling either. However, it may be painful while you are removing the scabs, so be very gentle and take your time. Many horses will be resistant to this.
How is rain rot treated?
Dermatophilus congolensis grows better with a lack of oxygen. Since the organism doesn't like oxygen, you'll have to eliminate a the heavy hair coat (if your horse's hair is long and thick), and remove any scabs that hold the organism to the horse's skin.
It is not a good idea to use ointments on rain rot, since they hold moisture to the skin (and moisture needs to be removed for the condition to cease).
The best treatment is to wash the horse with antimicrobial and antibacterial shampoos and rinses. These medications help to kill the dermatophilus congolensis organism. If Betadine, Phenol or Nolvasan is used, you should continue applying them once a day for one week.
1. Keep the horse in a dry, clean area that is very well ventilated. Give the horse protection against biting insects. Separate the horse from any others that also have rain rot.
2. Use an antimicrobal shampoo that lathers well. Vigorously lather the horse, let sit for 10 minutes, then rinse. Be sure to follow with a conditioner that works well. Continue this for daily for 1 week.
3. Remove all scabs that are present. This is usually painful for the horse, so be gentle! The best way I have seen to remove these scabs is to temporarily moisten them (so they become soft and easy to remove). Be sure to dry the horse immediately after scab removal.
4. The organism in the horse's skin must be killed. This can be done by using any of the products listed below.
SEVERE CASES ONLY: for severe cases, antibiotics may be used. These include potassium penicillin, procaine penicillin G, sodium ampicillin, streptomycin or gentamycin. Immune-boosting drugs may also be needed for the horse's immune system to fight off the organism and heal. If your horse has a severe case of rain rot, make an appointment with your veterinarian and discuss the antibiotics listed above.
References, Resources & Links:
Horsetalk - Solving the scald problem, by H. Steve Conboy, DVM
MyHorseMatters.com - Summer Skin Problems
Susan L. White, DVM, MS, Dipl. ACVIM, AAEP member, with Lydia F. Miller, DVM, AAEP Owner Education Director
Petalia: Rain Scald
Dr John Kohnke BVSc RDA
Horse & Hound Online: Treating Rain Scald
Tim Couzens MRCVS
HorseConnections - Rain Scald
Dermatophilosis (Rain Scald)
Client Information Handout: Virginia-Maryland Regional College of Veterinary Medicine, Veterinary Teaching Hospital.
HorseMatters.net - Skin Conditions
Mane Points - Rain Rot
Lucky S&L Ranch, Reference Library: Rain Rot
Rain Rot Remedies - R&K Croft Farms
Brief Notes on How Others Treat Rain Rot
ORSE BITS - Equine Winter Skin Problems
Equine Rescue League - Ask Bubba
Equiworld - Mud Fever