Fighting Those Infamous Fungi

Ringworm, girth itch, rain rot… what horse owners wouldn’t do to wipe these words from the equestrian vocabulary! Unfortunately, these determined fungi (or in the case of rainrot, a bacterium masquerading as a fungus) are not so easily eliminated. These relentless skin invaders have been a source of immense irritation to horses and owners alike for as long as anyone cares to remember. Though unlikely that we will ever be completely rid of these microscopic marauders, they are fortunately not entirely unconquerable.

Ringworm

Most equine managers cringe at the very mention of the word “ringworm” and immediately visualize a wildfire of balding circles inflicting themselves upon every warm-blooded creature on the premises. The fact is that ringworm can be caused by a number of different fungi, each with its own subtle differences and subversive tactics by which to invade a population virtually unnoticed until the fungal forces are well entrenched.

Perhaps the most common organism associated with ringworm is Microsporum gypseum. This is the culprit responsible for those instantly recognizable circular rings so commonly associated with the affliction. Microsporum is highly contagious and is easily spread through direct contact with infected horses, dogs, cats, humans, and diseased rats. The organism is also passed along via shared contaminated tack and grooming supplies, and on contaminated clothing. Thin-skinned animals, young animals, and those receiving inadequate nutrition are particularly susceptible to ringworm infections, as are any animals kept in warm, damp, filthy environments where the fungus is likely to flourish.

After exposure to Microsporum gypseum, incubation typically takes from one week to one month but may be shortened to as little as four to six days under ideal circumstances. The condition can appear overnight as raised patches in the haircoat with no accompanying bumps on the skin, or the first signs may be the appearance of increased skin scaling in one or two spots or over the entire body surface. The condition may then progress to raised welts, which in turn progress to crusty patches of skin and hair, one-half to one inch in diameter, which may spread all over the body. These crusts are both itchless and painless and can be peeled away as solid caps exposing a moist, reddish area underneath. It is also possible for this infection to be localized to the legs where it may contribute to grease heel, another uncomfortable skin condition afflicting the backs of the pasterns.

Treatments for ringworm have changed over the years. Captan washes are no longer recommended as Captan is suspected of possessing carcinogenic properties. Iodine preparations have long been used to combat fungal skin infections. Iodine, however, can easily burn sensitive equine skin and can be replaced by safer and equally effective products.

Both Nolvasan and Dermazole animal shampoos contain active ingredients effective against ringworm. Bathing the afflicted horse with either one of these shampoos every third day for three to four weeks will bring the fungus under control. There are, however, those situations and times of year during which bathing is simply not an option. In this case, clipping the hair from around the lesions and spot cleaning with one of these shampoos or applying Lotrimin ointment (the athlete’s foot medication available at drug stores) or Nolvasan topically to small areas of infection may suffice. It is important to wear gloves when treating ringworm lesions directly, as the most common ringworm fungi are transmissible to humans. Take care, also, to burn or discard any removed crusts or scabs to avoid reinfection.

If the infection involves large areas of the body surface, and bathing is not possible, consider treating the animal with griseofulvin orally. This treatment, too, is not without its flaws. Correct dosages of this product specific to the horse have never been researched; therefore, dosages may be inaccurate. Though horses are known to improve while taking griseofulvin, ringworm itself will run its course and spontaneously abate, making any curative effects of the griseofulvin difficult to determine. Oral thiabendazole may have some action against the ringworm organisms, although here again the dosage is vague and the therapeutic value unproven.

As mentioned, if left untreated, most horses will eventually self-cure from a ringworm infection. However, the duration of the condition is largely dependent upon management practices and environmental factors. Under ideal circumstances, spontaneous recovery occurs in six to eight weeks with hair regrowth beginning approximately three weeks after the infection has been brought under control. This natural healing process can be drastically undermined by well-intentioned yet ill-fated cold-weather care. Horses contracting the condition in early winter and kept in a warm but poorly ventilated barn with little or no exposure to the curative effects of the ultraviolet rays of the sun will likely be battling the fungi into spring.

Girth Itch

Girth itch is another member of the ringworm family; this one attributed to the organism, trichophyton equinum. In many ways similar to the microsporum branch, this fungi also prefers the most youthful members of the herd (though neither ringworm organism is actually restricted to any one age group); is spread through contact with contaminated tack, grooming supplies, and environments; is highly contagious; and will gladly infect a reckless caretaker as readily as every pasturemate. Tack friction also plays a significant role in the advent of this condition.

Trichophyton differs from microsporum in its appearance as clusters of small hairless circles, one quarter to one inch across, covered with tiny scales in the girth or rein area. These may balloon into larger barren patches or may form crusts as the surrounding hair falls out in clouds of dandruff. Though not painful, this condition is often mildly to tremendously itchy. Treatment for girth itch is identical to that for other ringworm infections.

Rainrot

Rainrot or rain scald is the final major skin malady to be discussed. It is most commonly caused by the organism, dermatophilus congolensis, which is not a true fungus, but a bacterium with fungal characteristics. True to its familiar name, this condition commonly attacks skin subjected to prolonged and constant wetting, as in animals left unsheltered during long rainy periods. Horses grazing frequently on pastures damp with dew or who tend to urinate in a manner which wets the legs may contract the disease on their lower legs. In this location, dermatophilus may also contribute to the development of grease heel. Poorly ventilated stabling where moisture retention and condensation are constant problems can also set the stage for a rainrot infection. Dermatophilus itself lives in dusty soil as well as in the dust of most horses’ haircoats where it quickly multiplies when mixed with sufficient moisture and skin secretions.

Malnourished animals, as well as those with inadequate shelter from moisture are particularly susceptible to this organism. Though, as with the true fungi, this bacterium can spread via contact with contaminated tack, equipment, and environments, only those animals whose skin is already vulnerable (wet or broken and oozing) are likely to contract the disease. Biting insects may play some role in the transmission of this organism from one animal to the next, as may skin left open to invasion through injury. Though not considered to be particularly contagious from one healthy, well managed animal to the next, rainrot commonly affects a number of horses left susceptible in similar circumstances at the same time.

Rainrot may initially take on a number of different appearances. The first evidence of an infection may be hot, tender bumps which are easier to feel than see. Or there may be one or more small crusts, two to four millimeters across, with lifeless hair protruding from the base which can be easily plucked from the skin. The infection may never progress beyond this point, or may spread out to create scattered, erect tufts of matted, crusted hair above the dripline on the horse’s back, rump, shoulders, and neck. These crusts will generally follow the runoff pattern of raindrops on the haircoat. There is no itch associated with dermatophilus, however, as the disease progresses, the scabby islands will harden and adhere more tightly to the underlying skin, causing great pain and revealing inflamed, purulent surfaces upon removal.

The affected areas should be cleansed carefully with one of the medicated shampoos previously mentioned in order to loosen the scabs and crusts for easier removal. Because moisture promotes this disease, the skin must be thoroughly dried after bathing. Nolvasan ointment can then be applied to soften the remaining crusts and kill the infective organism. All removed scabs and crusts should be burned or chemically treated to avoid spreading the infection. Dermatophilus can remain viable in scabs for up to forty-two months.

A combination of penicillin and dihydrostreptomycin (Combiotic, Pen Strep) administered intramuscularly once daily for fourteen days will further assist in a rapid recovery. Rainrot typically succumbs quickly to this assault. Healing should be evident within a few days of beginning treatment.

Left untreated, a dermatophilus infection, as with the ringworms, will usually spontaneously heal in eight weeks. Recovery may be hastened by maintaining the animal in perfectly dry surroundings until the condition has completely cleared. Hair in the affected areas will slip away but leave little or no permanent scarring of the skin. Hair regrowth should occur readily once the infection has cleared up.

Prevention

Of course, the easiest way to treat any skin condition is to do everything possible to avoid its occurrence in the first place. It’s the old “an ounce of prevention is worth a pound of cure” thing. Where these mighty stubborn fungi and bacterium are involved, however, it’s more like “a few hours of prevention are worth eight weeks of cure.” These organisms can survive under the right conditions anywhere from several months to several years and attach themselves to virtually every item and surface in your horse’s living environment. There is no significant immunity for the survivors of these unfortunate ailments. Left unmolested and viable in your barn, these skin invaders will find the next susceptible victim and continue to make their rounds time and time again.

So how do you break the cycle of reinfection or hopefully even avoid these nasty little problems altogether? All of these organisms can be eliminated from surfaces and supplies with a solution of one part bleach to twenty parts water. Disinfecting tack, grooming tools, stalls, fences, etc. periodically with this solution should be your first line of attack. Avoid sharing tack or tools between stablemates, and never share with an unknown animal. Do not allow horses new to your stable to come into direct contact with any other animal for at least the month-long potential incubation period for ringworm. Be careful, also, not to allow your horse to fraternize closely with others at horse shows, clinics, trail rides, etc.

Fungi are particularly susceptible to sunlight and hot, dry, clean environments. Aside from the obvious physical and mental benefits horses derive from time out in the sun and fresh air, there is little you can do to avoid or treat a fungal skin infection more effective than turnout on a nice day … but only on a nice day. Remember that rainrot loves dampness. You can easily avoid this infection by providing dry housing for your animals. When brought inside, horses should be kept only in clean surroundings with adequate exchange of fresh air.

The horses themselves can be made less susceptible to infection by also being kept as clean and healthy as possible. Regular grooming is the best way to keep a close eye on any problems popping up on your horse’s skin. Vacuuming the haircoat will help to reduce the dust which binds dermatophytes to your horse’s skin. Bimonthly medicated shampoos will further help to eliminate infectious organisms lying in wait on the surface of your animal’s coat. Attend to your horse’s overall health by providing an adequate diet and all necessary routine medical care. Do what you can to combat your horse’s exposure to biting insects which may spread infection and sources of injury that may break the skin, leaving it vulnerable.

And so, the battle lines are drawn. We struggle to keep our horses safe from such undesirable organisms as ringworm, girth itch, and rainrot. These invaders struggle to gain a stronghold in the environments we strive to protect. They are tenacious, but we are armed with strategies and remedies that assure us victory if we can only stay a step ahead of those infamous fungi.