Written by Emily McNally, VMD   Rappahannock Equine Clinic

With winter upon us, we can be sure to see a fair share of wet days over the next few months. Wet weather brings a myriad of different skin conditions that can be frustrating for horse owners to deal with. One of these conditions almost all owners have to deal with at some point is commonly known as “rain rot” and is one of the most common skin infections seen in horses.

The organism Dermatophilus congolensis is the causative agent of rain rot. These bacteria can be found dormant on the skin of many healthy horses and do not pose a problem until the skin is compromised in some way or infection is exacerbated by weather conditions. There is a certain natural immunity to the organism, but as many owners have seen, some horses are more susceptible to infection and can get rain rot year after year. Horses with heavy winter coats keep moisture in contact with their skin, producing an environment for the organism to grow. When the skin is damaged, such as with an insect bite or scrape, Dermatophilus congolensis can infect deeper down into the epidermis.

Diagnosis is usually made using observation of the clinical signs alone, but skin scrapings can be observed under the microscope to visualize the bacteria. Rain rot appears as large crust-like scabs or small 1/4 inch matted tufts of hair. Underneath these scabs the skin can be pink and irritated, and you may sometimes even see puss when the scabs are first removed.

Dermatophilus congolensis can be spread among horses through sharing of equipment such as blankets, brushes, saddle pads and halters. Try and have separate equipment for each of your horses. If you are unable to do so, the best prevention for spread of rain rot is to use a disinfectant on any equipment shared among horses after each use. A good solution for equipment sanitation is two tablespoons of Chlorox bleach to one gallon of water.

It is advisable to start treatment for rain rot when clinical signs first appear because it is easier to treat a less severe case than a more severe case. Rain rot can lead to secondary bacterial infections, such as Staphylococcus and Streptococcus infections, which are at times more refractory to treatment.

The best treatment against rain rot is to wash the horse with antimicrobial and antibacterial shampoos such as betadine or chlorhexidine, which help kill the causative organism. You can continue applying these shampoos once a day for one week letting the lather sit on your horse for 10 minutes before rinsing. It is generally not a good idea to use ointments on rain rot because they hold moisture to the skin.

For severe cases, an examination and advice from a veterinarian may be required. Your horse may have an underlying condition causing its immune system to become depressed, thus giving it higher susceptibility to the organism. Blood work may be run to rule out systemic disease. Antibiotics and immune boosting drugs can also be employed to help get your horse’s coat back to being sleek and healthy.

If you have questions about rain rot or any other concerns about your horse’s health, please don’t hesitate to call our office at 540-854-7171.