Rain Scald

Rain scald, or rain rot, is also called streptothricosis and is caused by the fungal organism Dermatophilus congolensi.

The organism is dependent on a carrier horse who has the organism on its skin, and who may or may not be affected by it. Contrary to what a lot of people think, the organism has not been demonstrated to be present in dirt or soil.

There is some natural immunity, but some horses seem to be more susceptible to it, and that’s why some horses get it year after year.

In order for a horse to get the disease, some conditions have to exist.

¨ an infected carrier animal, or

¨ an item such as a brush, blanket, or saddle that has the organism in the form of a spore that makes contact with the susceptible horse.

¨ some form of extreme moisture, like heavy rainfall, hence the name.

¨ horses that have heavy coats keep the moisture in contact with their skin, which helps the spores grow.

¨ the skin has to be damaged – from an insect bite, cut, or scrape. That lets the organism get down into the skin

Getting the scabs off and letting the air get to the ulcerated areas is most important.

Rain scald is somewhat a self-limiting disease. The horse will probably get over the problem as it sheds its coat. The organism prefers carbon dioxide or a lack of oxygen to grow. So, you need to get rid of the heavy hair coat and the scab that’s holding the organism into the skin.

The first thing we do is use a soap – like an iodine, or chlorhexidine soap– that lathers good and work that crust off that’s created by serum oozing out through the skin. With gloves on, lather the horse good and try to break the scabs off, which is painful to the horse. Getting the scabs off and letting the air get to the ulcerated areas is the most important part, and it is the most difficult because the horse resists it. Since it’s painful, sometimes it takes a couple of days working a little at a time. If this occurs during the winter it is very difficult to make sure the scabs are exposed to the air while still remaining dry, often stabling is necessary. In cases where this is not possible make sure the horse is completely dry before putting its cover(s) back on. Often the cover will also need to be treated aswell to prevent re-infection.

There are complicating factors occasionally. Because this disease causes a moist, warm environment, it’s a good place for a secondary bacterial infection like staph, strep, or Rhodococcus . The case can be more difficult to treat, and it might require systemic antibiotics. The Dermatophilus organism itself is very susceptible to penicillin, so your veterinarian may prescribe that for severe cases.

Rain scald or rain rot can manifest itself in several ways.

The best way to prevent spread of the disease is to use some form of disinfectant for brushes (like Vircon) and wash your hands thoroughly after working with an infected horse. Blankets shouldn’t be used between horses, but if they are, they should be washed and disinfected before being used on another horse.

It’s important to disinfect anything you use on an infected horse before using it on another horse: halters, saddle pads, brushes. Even if the horse has a favorite place he rubs, like a stall door or a fence, it can become a source of the organism.

Diagnosis is usually by clinical signs, and the disease can manifest itself in several ways. It can result in rather large, crusty, circular areas. It can also be in small, raised areas with small scabs (less than one-quarter of an inch). When it’s like that, there will be a mass of raised hair all over the horse’s back. In either case, there is a crust of serum that elevates the hair. As the disease progresses, the crust may increase to a quarter of an inch thick.

The disease is not usually associated with any discomfort or itching except when you remove the scab, which is painful. When you remove the scab, the skin underneath might be gray and healing, or pink and oozing.