Page 41 - Speedhorse Canada Spring 2020

RAIN ROT (RAIN SCALD)
“We don’t commonly see this
in a dry climate, but rain scald is probably the second most common wet-weather skin problem in horses,” says Evans. “In my practice, we see it mainly in winter when horses have snow on their backs and it melts and runs down their back, similar to a horse that’s standing out in the rain a lot.
“The causative organism is Dermatophilus congolensis, which is
a flagellated anaerobic bacterium. It’s probably a prehistoric bacterium, compared with some of the others such as staph and strep. The pathogen that causes rain scald has more ancient DNA.
“There are probably carrier horses, and if conditions are right they can spread it to other horses through direct contact. Rain or wet conditions may trigger active infections if there’s a break in
the skin. Horses with rain scald have a typical crusting hair loss, generally on the topline and down the buttocks and neck—but predominantly over the back, shoulders and rump. Rain scald tends to have a recognizable clinical appearance; the lesions almost look like water beading off the horse, like a drip pattern. The crusts generally correspond with that pattern.
“We can examine samples of
the crusts under a microscope and see the flagellated bacteria. They have what’s called a railroad track pattern. These skin scrapings are diagnostic and we don’t have to send them to a pathology lab; we can usually recognize them ourselves,” Evans says.
Treatment is topical. “We
like to keep these horses dry,” he explains. “We first wash them really well with chlorhexadine soap to remove the crusts and then apply
a chlorhexadine ointment to the affected areas. Generally, the lesions respond favorably if we can then keep the horse dry. If the horse lives outside and we’re having constant rain, I encourage the client to keep that horse inside. If we’ve just come through a rainy period and the client recognizes that the horse has rain scald and we’ve treated it, and we now have nice weather, I like to see those horses out in the sun, in dry conditions.”
Rain scald can be a cosmetic issue because a large area of the horse may be affected, with hair loss. “Clients wonder if the horse is contagious, but if you are actively treating the horse and keeping it dry, this condition is not any more contagious than
the horse was prior to getting it,” he says. “We don’t know which horses are carriers; we generally just treat the affected individuals.
“Rain scald is generally not as frustrating as scratches, because scratches tends to recur over and over again, if conditions are right. Rain scald seems to be more of an intermittent problem, depending on the weather.”
Rain scald lesions can be painful, and the horse may not be able to wear a saddle until these areas heal. “In some cases we have to use anti- inflammatory drugs, such as non- steroidal drugs like phenylbutazone to manage acute pain. On occasion, in horses that seem to have an auto-immune component, I use
low dose steroids for 7 to 10 days to get the pain and swelling under control. Most of the cases I see, however, are not very painful— particularly if we get the crusts off. The chlorhexadine cream acts as a soothing salve,” Evans says.
RINGWORM
“This is another common infectious condition,” says
Evans. “The medical term is dermatophytosis; the fungal organism is a dermatophyte that lives on skin. There are a number
of fungal organisms that can cause ringworm. Most of them can affect all species and not just horses. When a horse has ringworm, it could
be spread to humans and other animals. I encourage horse owners to be careful and use gloves when handling or treating the horse. If their immune system is suppressed for any reason (stress, chemotherapy, etc.), they would be more likely to get it themselves.
“We typically see ringworm
in a random distribution. It is
not as dependent on weather or management. The horse may have a suppressed immune system for some reason and this allows the fungal organism to become established. Signs are patchy hair loss—anywhere on the body, but typically on the trunk, head and neck. We don’t see lesions as often on the limbs.
“One of the characteristic signs, if you examine around the margins of where the hair is lost, is that you can easily pluck the hair. It readily comes out in tufts around the edges of the hairless area. This is different from a typical rub mark that some people might think is ringworm. If
SPEEDHORSE CANADA Spring 2020 41
EQUINE HEALTH