While we would like to think at times we are all experts in a particular field, the term “expert”
should be attached to a person (s) who have the clarity to recognize that someone is more
proficient than they might be. This would be the case with this paper. Heather Smith Thomas
published a report in the January 2001 Issue of Anvil Magazine from which much of the
information included in this paper is derived. It is by far the most accurate assessment of this
skin malady that we have researched. Kudos to Ms. Thomas for her insight and presentation
skills! “Scratches" is a term that refers to a skin dermatitis problem of the deep layers of skin
of lower legs of horses and cattle. It is a caused by a fungus, specifically Sporotrichum schenki, which in its most advanced form can have a bacterial component. It is most prevalent in the pastern and fetlock area and manifests itself as thicken black and crusty scab like bumps. Due to the location of the sores and the constant movement in the joint area, the skin will move and crack, leaving festering abscesses. Left untreated, the open sores allow the bacterial component to invade inner tissues and even vascular and lymphatic vessels. When this occurs, the whole lower leg may swell and the horse may become lame. Treatment at this point is complicated due to the combined bacterial/fungal components.
The myth about scratches is that it is “inherited” or that it occurs only in horses with white leg
markings. Like any disease or infection, some animals are more susceptible than others. The
fact is that unpigmented skin is more prone to chaffing and abrasion, thereby allowing the
infectious organisms to enter the body. Fungal and bacterial organisms need a break in the
skin in order to infect tissue. Other common fungal infections which act in this manner are
ringworm and girth itch. Both the fungus and bacteria which cause scratches are present in
moist and organically contaminated pastures or corrals. While not specifically identified, the
bacteria which works in concert with the fungus is more than likely anaerobic, which means
that it requires little or no oxygen to live and thrives in moist and manure like environments.
A variety of different treatments for scratches have been used over the years with limited
success. They include nitrofurazone, topical steroids, bactericides, iodine based chemistries
and a variety of home remedies and ointments. One such treatment is a mixture of
thiabendazole (cattle wormer), DMSO (dimethy sulfoxide) and nitrofurazone. There are
number of issues with creating these “compounded” mixtures. First, from top to bottom these
remedies contain chemistries which may be included on the banned substance list for
performance horses. DMSO has been used for years as a “carrier” solvent. Used alone it can
burn or irritate tissue. When mixed with chemicals such as iodine it can cause serious
problems. It will also readily show up on a urine or blood test. Second, it is difficult securing
many of these chemistries; which should tell you something about their safety. With certain
components such as thiabendazole not being readily available, it was substituted with
fendendazole, cambendazole and oxfendizole.
There are additional issues with this tact. Do the people using the products have any idea what
they are applying to their animals? Has there been any research detailing what the
compounding effects of mixing these chemicals together is? Do people realize that some of the
recommended chemistries are listed as being carcinogenic?
Third, with the combination of a fungus and unidentified bacteria, the “throwing” of chemicals at the infection in hopes that it will work allows the organisms to develop immunity to treatment. Drug or chemical treatments are designed to poison the infectious cells. If 100% of the cells are not eradicated, the organisms have the ability to mutate through a complex chemical work around. It not likely that 100% of the cells will be killed in the environment which horses and cows exist. It is however likely that the organisms have engaged in a mutation process based on the difficulty that people experience in eradicating scratches.
There is also another remedy that is being promoted. It is the all natural, essential oil, tea tree
oil formulation. There are two weaknesses with this treatment regimen. First, the bacteria
that co-exist with the fungus are anaerobic. Applying essential oils serve only to prevent
oxygen coming in contact with the infection. Oxygen is an effective agent in the deactivation of
this type of bacteria. Second, while tea tree oil has been evaluated as a bactericide, it has no
specific effectiveness against fungal infections, the predominant infection causing organism.
To be fair, depending on the extent and nature of the infection, this remedy would be
preferred over the drug therapy.
There is a natural alternative for the treatment of scratches. Summit Animal Health’s
technical staff researched this problem for over two years before developing a solution. The
SAH uses a 3 Step Process. The effectiveness treatment is based on the EnvizO3-Shieldtm