Scratches and leg mange are characterized by very similar symptoms in equines but the causative agents and treatment of the two conditions are very different.
Scratches, also known as greasy heel, dermatitis, dew poisoning, mud foot or verucossa, can be caused by less than sanitary conditions and a resulting infection caused by bacteria, fungi, or virus. “Scratches” is characterized by slowly enlarging redness, crusts (scabs), and open sores on the back of the heels, pasterns and fetlocks. Unchecked this condition may spread even further up. The sores are painful and can cause lameness. Along with scabbing, you might find hair loss or areas of blood, fluid or puss. Most commonly the affected area is observed on the hind legs. Treatment usually consists of antimicrobial, anti-fungal and anti-inflammatory agents.
Leg mange, also known as Chorioptic mange, foot mange, or heel mange is caused by a small insect called a mite. Chorioptes equi is the most common type infecting horses. These microscopic mites have eight legs and are closely related to spiders. Scab like lesions will be observed below the knees and hocks on the lower limbs with crusts and sores on the thickened skin. The wounds are caused by the mites puncturing the skin to induce fluid they can then feed upon. The mite’s feeding causes intense itching and affected horses will stamp their feet, chew their legs and rub their legs together in attempts to alleviate the itching. In long standing cases the skin often becomes severely thickened with deep creases, and permanent damage can occur. These mites do not transmit to or infest humans or other species and are exclusive to the equine family. There is a higher incidence of leg mange and scratches in the draft horse breeds, especially those with thick feathers such as Shires, Clydesdales and Brabants.
It is important to attempt to determine whether you are treating scratches, leg mange or both. The symptoms can be very similar and the two can exist concurrently. This is because once the skin is damaged by the mites it easily becomes infected by the opportunistic bacteria, fungi, viruses commonly found in scratches. If mites are present and traditional antimicrobial and anti-inflammatory treatments for scratches are used without treating with an insecticide, the mites will not eliminated and the process will start over. In the experience of Doc Hammill, DVM, it is common to treat draft horses for what is thought to be scratches without being aware that the underlying cause is leg mites. A microscopic exam of scrapings from the lesions is the diagnostic test used to confirm the presence of the mites. However, it is not uncommon for even multiple skin scrapings to come up negative, when in fact mites are present and causing the problem.
Contrary to common recommendations, Doc Hammill advises not clipping the hair on the affected legs. His experience has shown clipping or shaving can make the skin problems worsen whether they are from scratches or leg mange.
In his 1886 book, Magner’s Standard Horse and Stock Book, the legendary horseman, Dennis Magner, states: “Clipping the hair from off the legs is regarded as a very serious cause of scratches, as it leaves the skin so bare that it cannot readily resist the effects of irritants of any kind as when protected by its natural covering; but the most common cause is the habit of washing the legs with cold water, and not drying them thoroughly afterward. The sebaceous glands in the hollow of the pasterns become inflamed, their secretion is increased, the skin cracks, and discharges an ichorous matter.”
Doc first completely cured a case of leg mites in one of his own horses in the 1970s by experimenting with a powerful dose of an insecticide for mange in hogs that was later banned. So for years he was limited to the use less effective leg mange treatments and mineral oil in his practice and with his Clydesdale horses. Unfortunately, mineral oil and many other treatments typically only reduce mite populations and alleviate symptoms temporarily rather than eliminating the mites completely.
Injectable ivermectin is no longer licensed for use in horses due to some problems with infections at the injection site. However, many veterinarians have found injectable ivermectin products for cattle (such as Dectomaz) to be reasonably safe and very effective when used in horses, IF: (1) injected into the muscles of the thigh, (2) the injection site is surgically prepared, (3) absolutely sterile injection technique is used. Consequently, Doc Hammill recommends having a veterinarian administer the ivermectin injections. It is imperative that the hair be shaved off of the site and that the area is surgically scrubbed and disinfected before injecting. A new sterile needle must be used for each injection and it should touch nothing except the freshly sterilized stopper on the ivermectin bottle prior to the injection. Sterility is of utmost importance to prevent potentially dangerous infections. Many veterinarians will not administer ivermectin to horses by intramuscular injection since it is not licensed for use in equines. If you find one who is willing to inject your horse(s) with ivermectin they will likely require you to sign a liability release first.
Thanks to the advent of ivermectin we now have the potential to eliminate Chorioptic mites completely and cure long standing and severe leg mange with a very specific treatment regime. In Doc’s experience ivermectin administered orally or topically will affect mite populations, but the results are often transitory. On the other hand, the cure rate is excellent when ivermectin is administered by intramuscular injection, and even better when accompanied by topical treatment with a specific flea and tick spray, and followed by rubbing mineral oil into affected leg areas between the series of injections.
Since treatment does not destroy mite eggs the ivermectin dosage must be repeated every two to three weeks, to not only kill the adult mites present initially, but to also kill the newly hatched mites before they can lay more eggs and re-infest the host. The timing is critical. Doc Hammill recommends a minimum of three treatments. The first treatment is to kill the existing adults, the second to kill the newly hatched and the third to eliminate any late hatching survivors.
For long standing, severe cases or cases resistant to treatment Doc includes a topical insecticide for dogs and cats called fipronil which is marketed as Frontline Flea Spray. Doc shies away from using insecticides in general, but spraying the legs once on the day of the ivermectin injection and once a day for two more days has helped cure some tough cases. Wear rubber gloves to rub the product into the hair and skin thoroughly. Whether you use the spray or not Doc recommends treating the legs with mineral oil between injections and for a few weeks afterwards.
If you are reluctant to use the injectable ivermectin regime your veterinarian might be willing to prepare a topical ivermectin, antibiotic, anti-inflammatory ointment for you. Wear rubber gloves and thoroughly rub the mixture into the affected skin areas 2 to 3 days in a row at intervals of two to three weeks. Treating the legs with mineral oil between ointment treatments will improve success. However, Doc warns that the results are often temporary except in some early and mild cases.
Mineral oil is easily found and purchased from most general merchandise stores. To purchase gallons or larger quantities, the horse owner can obtain supplies from a veterinarian or a bulk oil distributor. Application is simple. Rub the oil into the affected skin areas of the leg twice a week initially and then once a week or every other week for maintenance after the lesions are healed and the itching gone. Plan a regular schedule and massage the oil thoroughly into the affected skin areas. A handy way to dispense the oil is to fill a plastic liquid dish soap bottle with oil and use it to squirt the oil onto the leg and rub it in. When the oil begins to soften the crusts and scabs, gently rub and pull them from the hair each time you treat the area. Accumulation of dirt on the hair can occur with the application of the oil but does not seem to be problematic. The oil seems instead to provide a necessary barrier for the skin against future dirt and moisture.
The key to success is to treat each leg thoroughly and regularly. There is no need to pick up the horse’s feet during treatment. Horses unwilling to have their legs massaged in this manner need to have some daily grooming and desensitizing by grooming further down the legs each day until they are comfortable with your hands on their legs and feet. If the horse is really difficult, you can loop a rope around the upper leg and rub it back and forth around the leg, gradually working up and down the leg until they can accept the touch. Switch to using your hands only after the horse is non-reactive to the rope.
The supposition is that the oil suffocates the mites by plugging their breathing holes. The oil is beneficial to the skin of the horse regardless if suffocation is the effect on the mites. Doc wipes the excess oil from his hands after a treatment onto the horse’s mane and tail to make them shiny and soft as well.
It is extremely important in the treatment of leg mange to treat all of the horses that have contact with one another, and to treat them on the same schedule. It’s also a good practice to check any new horses for symptoms before they come on to your property. A horse does not need to have visible symptoms to be carrying the mites and passing them on to other horses. Close contact between individuals is the most proven way of contamination. There are some claims that mites can live in the horse’s bedding for several months but those claims have not been proven. To be safe, removing bedding from the area is never a bad notion. Power spray the stalls a couple times during the treatment process if possible. You can also clean the stalls and then let them stand for two to three months without horses in them to out wait any mites.
In summary, there are potential sources of bacterial and fungal infections everywhere. Scratches can appear as a single condition or be the result of a condition created by leg mites. Keep barns, corrals and legs as reasonably clean and dry as practical and use mineral oil as a grooming habit. Disinfecting grooming equipment with bleach and water occasionally can also help prevent the spread of unwanted skin conditions.
Originally published in Rural Heritage, Spring ’08