The Canker : Chronic Hypertrophic Pododermatitis

The origins of canker are multiple and have not been completely brought to light yet. With only few cases, this pathology is often poorly known or even unknown by horse owners as well as farriers and / or veterinarians. Its complete medical name is Chronic Hypertrophic Pododermatitis (CHPD). “Pododermatitis” means skin infection; “chronic” as it is periodic and “hypertrophic” because a tissue or organ is abnormally over developed. It is not tumour-induced. It is therefore not a hoof “cancer”, as there is no (even benign) tumour.

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Unlike thrush, which regularly affects five million horses in the United Sates and four million in Europe, canker is hopefully quite rare, although no study has been conducted to determine its prevalence.
It is however a serious pathology which can be fatal if no suitable treatment is provided.

Equine canker is a chronic inflammatory disease of the hoof derma, coming along with often deep and infected lesions secreting big quantities of foul-smelling pus.

It also presents raised and soft, wet and proliferating tissues, looking caseous as soft cheese or yogurt, with a significant vasculation. Trimming hypertrophic tissues (abnormally over developed) leads to abundant hemorrhage and can be very painful to the touch.
Coronary bands are swollen and the horse can hardly step on its hoof, or even move. Overgrowths of the horn are frequently well visible at the back of the frog, and it is unfortunately very common to notice that several hooves are simultaneously affected.
Another characteristic of CHPD, which may explain its English name canker, is its invasive tendency to easily spread from the initial lesion (e.g. the frog or the heel) to all the nearby tissues, including the sole chorion and the hoof wall.

This phenomenon starts with a chronic hypertrophy of the tissues producing the hoof horn, i.e. an overgrowth due to the increasing size of the cells.
These degenerated tissues, of a very poor quality, are then very easily contaminated by a series of pathogenic germs (bacteria, fungi, protozoa), which explains the quick emergence of deep, purulent and spread infections.
Isolated and specific bacteria are varied.

A few examples are the Spirochete (spiral-shaped soft bacteria without a rigid shell), the basophile bacteria (living in alkaline means – ammoniac – urine), the Fusobacterium Necrophorum or the Dichelobacter Nodosus (negative gram) living in the absence of air oxygen (anaerobia), positive gram like Bacillus and many others. They spread through soils (pastures and/or wet beddings, muddy grounds) where they can survive several weeks under favourable humidity conditions and average temperatures (above 10°C). These germs are located on all the infected animals, including the equine as well as the bovine animals, sheep and goats, etc.
All these fungi (this is a non exhaustive list) are cosmopolite, which means they are found in any area of the world. They are aerobic; therefore they live in presence of the air oxygen. They develop on various substrates high in organic matter: beddings, manure, excrements, sludge, waste water, vegetal waste, etc. which is the reason why they are also called “saprophagous”.

Compared to the usual and well-known thrush, canker shows distinctive signs. Both canker and thrush have an infectious component.
The bacterial and mycosic (fungi) strains that can be found in both thrush and canker are identical or very similar.
However, in the presence of canker, a highly inflammatory reaction can be noticed, as well as acceleration and an anarchic and chaotic renewal of the conjunctive and underlying tissues of the hoof (keratin).

The latter therefore look gelatinous, milk-white and inconsistent.
Many studies and researches have been conducted over the last year, but the precise causes of canker remain undetermined.
A systemic (general) or local immune weakness could explain the cases of canker observed on animals less vulnerable to health problems identified as responsible for the onset of the disease.
Because of both difficulties and length of its treatment, this pathology is often considered as incurable.

If Canker is discovered and therefore diagnosed before the hoof has been severely damaged, prognosis is often favorable. However, the latter will be uncertain when the sensitive structures of the hoof are unfortunately already damaged.

It is therefore important not to wait, but to act quickly and to call a veterinarian.

Factors helping canker to develop:

-Inappropriate use by the horse owners of various topic treatments (for local use), which are often caustic, corrosive, aggressive, irritating, inefficient to treat frog thrush, and cause a chronic irritation of the derma and therefore inflammation.
-A repeated deep thrush of the frog due to lack of efficient treatment is a triggering factor of canker.
-Lack of hoof and/or environment (bedding) hygiene, excess of humidity, closed and badly ventilated areas, are all determinant vectors contributing to the onset of the disease.
-Decomposing organics (feces, urine) release big quantities of ammonia, a highly irritating substance which leads to lesions and inflammatory irritations when constantly in contact with the sensitive structures of the hoof.

The origin of the disease may also be traumatic and the latter can thus appear due to an injury (hoof cracks, contractions of the hoof, lamellar injuries, etc.) Seasonal factors due to weather conditions are usually reported. Warm and wet periods are favorable to the onset of the disease. Horses with long heels are more up to developing this disease, as well as the heavy horses with rich fetlocks seem to be. This is sometimes mentioned, but poorly documented.

Treatments:

Treatments must be performed by veterinarians.

The surgical approach:

The therapeutic approach first consists in a complete and careful surgical debridement and curettage of all the epidermal parts having an abnormal visual aspect, until the inferior layers, with a firm, rosy and non exudative appearance.
Depending on the seriousness of the case, a local or general anesthesia will be necessary.

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The surgery can be long, as it is imperative to scrape all the abnormal tissues, and to explore patiently all the crevices. As the tissues to scrap are often soft, the used tools must be extremely sharp.
Even with an antiseptic bandage applied for 12 to 24 hours before surgery, the operating field is never sterile, as pathogen germs are still highly concentrated around the cankered tissues.
Unfortunately, it is not unusual to have to repeat the surgery several times. Indeed, despite all the careful operative actions of the vet, the disease is sometimes not totally controlled and recurrences appear during healing.

Care shall be provided every two or three days in order to help all the hoof structures rebuild. Over that period of time, a careful cleansing of the necrotic residues (dead tissues) and other small tissue debris will be done using a small soft brush (toothbrush). The healthy tissues shall not be irritated, and antiseptics (antibiotics) will often have to be used to avoid secondary infections. The hoof shall be wrapped in a bandage. The bedding shall be clean and dry.

Therapeutic trials:

A lot of therapeutic trials have been conducted alone or together with surgery in order to try to cure canker.
Among these, are found formalin solutions (often 10% concentrated), 50/50 mixes of phenol and iodine, Norwegian tar, sulfuric acid, fats as lard, and many more…
All these preparations are to be banned as they are irritant, caustic, and dangerous or lead to infections (Norwegian tar, fats).
Antibiotics in systemic (general) or topic (local) use are often needed or advised (Penicillin – Sulfa pyridine – Metronidazole).

Over the last ten years, two interesting studies have been conducted on the trial of new treatments.

The first one was realized by Dr Stephen E. O’Grady and his team (equine clinic « Northern Virginia Equine » in Virginia, United States) and the second one by Dr Hans Castelijns (veterinarian clinic of Cortona, Italy).

The first study consisted in doing a post-op follow up using topic (local) applications with a mix of 10% benzoyl peroxide in acetone associated with metronidazole.

Daily care was provided until a keratinized tissue appears with a healthy consistency. It was recommended to provide antibiotics (chloramphenicol and oxytetracycline) by mouth, although the authors consider that the observed results are exclusively due to the experimental treatment.

The combination of a debridement and a complete and careful curettage, together with the local use of the benzoyl peroxide solution in acetone and metronidazole has given very interesting, satisfying and coherent results, foreseeable in fifty-six cases, between 1998 and 2004. Only one recurrence has been noted.

One major problem nevertheless remains, that is the daily use of the benzoyl peroxide solubilized in acetone.

Indeed, benzoyl peroxide is a highly reagent product. It is explosive when dry. It can be stored in its solid form only if 30% of its mass is humidified with water. It is irritating. For these reasons, it can only be available in 4% to 5% doses.

Acetone is a highly flammable, irritating and toxic solvent.

Risks are therefore really present during preparation, storage, and use of this kind of remedy outside a totally secured experimental or professional environment.

In the second study, one can read that the author has successfully treated 65 out of 67 cases of canker. And that the two failures are not directly linked to the tested preparation.

The approach is the same: a complete and careful surgical debridement and curettage, but this time with a post-op follow-up using powder compound made of 50% picric acid and 50% salicylic acid. This treatment is repeated every two or three days until a keratinized tissue appears with a healthy consistency. Exudative phenomena disappear within two or six weeks following the surgical intervention.

The difficulties mentioned by the author are the followings:

«Practical problems can be summarized to the difficulty to find non-hydrated picric acid in dry powder because of its high affinity for water molecules making its in-depth action more effective on wet, exudative tissues. Besides, picric acid is not really pleasant to work with, as it irritates skin and mucous membranes, and it is toxic by ingestion».

It is indeed very difficult to find non-hydrated picric acid, mainly for two reasons:

  1. Its high capacity to fix water (the mere humidity from ambient air)
  2. Picric acid, hydrated or not, is an extremely dangerous product to handle as it is explosive. Its hydrated form (over 30%) is a little more stable but still remains hazardous. It can only be packaged or stored in glass containers. Crystal containers cannot be used as this contains lead, and metal containers (in copper etc.) can even less be used, as this acid would form picrates, which are extremely unstable and explosive.

Risks therefore really exist during preparation, storage and use of this type of remedy outside a perfectly controlled experimental and/or professional environment.

As for salicylic acid it is a safe and natural product extract from the willow tree or wintergreen, with well-known anti-inflammatory virtues.

Towards a new therapeutic approach:

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Having met all these difficulties, we believed it was necessary to start new researches and examine the therapeutic potential of safe and efficient natural therapeutic substances.

We focused on Curcuma, a plant of the ginger family (Zingiberaceae) with powerful and well-documented anti-inflammatory and anti-oxidizing virtues.

Our research center has developed Canker Care, a liquid preparation made by extracting the active principle of this plant. Several equine veterinarian clinics in Canada and Europe work together on the trials of this new treatment.

The first results (nine hooves affected with canker on five horses) are really encouraging.
The methodology is the same: a complete and careful surgical debridement and curettage with a post-op follow-up using Canker Care.

The treatment is repeated every day, or every two or three days (depending on the severity of the cases and / or the practical aspects) until a keratinized tissue appears with a healthy consistency. Exudative phenomena disappear within two or four weeks following the surgical intervention.

On the five horses currently treated with Canker Care, only one (partial) failure has been observed due to an insufficient post-op follow-up by the owner.

Canker Care therefore represents a real hope and even more, an original and interesting therapeutic perspective to heal canker using a product which is both safe and natural.