by Ashley Daily
Rain rot, sometimes called rain scald, was once thought to only affect neglected horses. However, even impeccably cared for horses were known to develop the condition. This led researchers to determine that rain rot was caused by a bacterium known as Dermatophilus congolensis.
D. congolensis often resides dormant on a horse’s skin. Exposure to moisture for an extended amount of time will activate the bacteria, causing it to spread and potentially infect the horse if it finds a break in the skin. Once D. congolensis enters the skin, a rain rot infection can be identified by small gray-white scabs clustered along the horse’s body, usually along the back and hindquarters. But rain rot can appear anywhere on the body.
“A lot of the time I’ll see it along the frontside of the cannon bones,” says Logan Kembel-Whitfield, DVM, of Equine Medical Associates in Edmond.
Symptoms & Treatment
Rain rot symptoms often appear a few hours after a horse comes in from the rain. While attempting to smooth out your horse’s ruffed-up coat, you’ll notice heat emitting from the skin and your horse flinching when the area is touched. These are the first signs of a brewing rain rot infection.
By the next day, the characteristic tight scabs will have appeared, ranging in severity from small, peppered scabs to a painful sheet. Tufts of hair, having a paintbrush appearance, will then appear over the scabs. If the scabs are removed, the skin underneath will be red, raw and contain yellow-green pus. Rain rot can sometimes mimic other skin conditions (and vice versa), such as ringworm, photosensitization and insect hypersensitivity. So if you’re unsure of what you’re seeing on your horse’s coat, call your veterinarian for a definite diagnosis and correct treatment plan.
D. congolensis thrives in an oxygen-free environment, so it’s sometimes recommended to remove scabs to allow air and sunlight to reach the affected area. However, removing scabs before they are ready to release can cause other issues.
“It can be really painful if you’re sitting there picking on them, and they’re not real loose,” Kembel-Whitfield cautions. “So get them wet first and soften the scabs.”
Bathing the area with medicated shampoo can help release scabs, as well as applying mineral oil and soaking with warm water. Soft rubber curry combs can be beneficial during bathing, but avoid using metal curry combs that can scratch the skin and cause the bacteria to spread. After removing scabs and hair tufts, place them directly into a plastic bag and dispose of them in a secure trash bin — or better yet, burn them. The bacteria can live in the scabs for several months, potentially infecting other animals.
While rare, cats and dogs can also contract the condition. Rain rot can be transmitted to humans, and although Whitfield has not personally encountered a human case, she advises wearing gloves when treating an affected horse. Hands should be washed thoroughly before handling other horses, and brushes used on infected animals should be disinfected by soaking them in a mild bleach solution for at least 10 minutes, then rinsed thoroughly and dried in the sun.
Usually, D. congolensis lives in the horse’s coat without causing any problems, but certain individuals, such as horses who have Cushing’s or those on immune-suppressing medications such as corticosteroids, can be more susceptible to developing rain rot. In healthy horses, rain rot will often resolve in approximately two to three weeks, usually only requiring an antimicrobial shampoo and topical treatments to speed recovery. In severely affected horses, an oral or injectable antibiotic might be prescribed.
Home Remedy Caution
You may hear about a variety of home remedies that claim to clear up rain rot quickly, but they should be avoided. Treatments such as white vinegar, mouthwash and essential oils are largely ineffective and may further irritate the skin. Your veterinarian can help determine the most appropriate treatment plan for your horse’s specific needs.
Rain rot is relatively easy to treat, but prevention is always best. Ensuring horses have access to shelter during rainy weather is critical in helping to prevent rain rot. It might be necessary to outfit more susceptible horses in lightweight rain sheets. Sharing tack, especially saddle pads, should be avoided, and each horse should have his own set of grooming tools to prevent spreading D. congolensis from a horse who is able to keep the bacteria in check to one who might be more sensitive.
Not every horse will develop rain rot, but by practicing good biosecurity and beginning prompt treatment at the first sign of infection, you can reduce the risk that crusty scabs will overshadow the growth of your horse’s new spring coat.
