The Outbreak of Equine Onychomycosis
by: Burney Chapman, C.J.F, Lubbock tx
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(White Line Disease) in the U.S. and the U.K.
1985 through 1992

Onychomycosis (ONC) is not painful in the early stages and is not taken seriously by the farrier or the veterinarian until the horse becomes lame or the wall can no longer hold a shoe. If the disease is not treated properly it can cause chronic changes of the PIII, the tendons and the ligaments. It can be present in any or all feet. The breed of horse/donkey or the color of his feet seem to have nothing to do with the disease, it is very non-biased.

Presently only local treatments and diagnosis of this wide spread disease have been tried. It has been suggested that yeast such as Candida Albicans is the responsible culprit. However in a total of 24 horses with advanced cases of ONC, a yeast has not been identified, only fungi species. ONC has been labeled as a disease of the white line. ONC is not a disease of the white line or the lamella structures, but attacks the stratum medium of the hoof wall. Dominant fungi found to date:

Scopulariopsis Spc. 6 Pseudallescheria boydii 11
Trichophyton Tonsurans 1 Acremonium Spicies 1
Microsporun nanum 1 Chaetominm Spp. 1
Trechosporon pullulans 1

The common denominator of the disease is high humidity or a high moisture environment. The guilty organisms are opportunistic and invade quite rapidly when conditions become suitable. In the early stages it can be treated successfully by opening the lesion and exposing to the atmosphere. Most horses/donkeys diagnosed with ONC were well kept, well shod, and were on a good medical and nutritional preventative maintenance program. Primary bedding used have been wood by-products, shavings, etc. Of the 24 head of horses in the advanced, chronic stage all have been biopsied and fungi have been identified in 22 of the 24. 21 additional horses have been diagnosed with ONC, but biopsies were not taken because of expense. 5 of the 45 head had reoccurrences in at least one foot from 1 to 4 years after initial diagnosis and treatment.

Treatments of ONC have varied. Topical application of strong Iodine, formalin, bleach, pine tar, turpentine, unleaded gasoline, DMSO, DMSO and Metrinitozol have all been used with a very low percentage of success. Complete debridement of overlying horn and subungal debris, plus topical application of tincture of Merthiolate were highly successful while 10% Benzoil Peroxide proved to be the second best treatment. All horses were shod with heart bar or full support shoes and hospital (inspection) plates on ground surface of the shoe.

Research needs to continue to find the causes and early recognition of the disease. The question is: "Why it is epidemic now and not prior to 1985?"

© Burney Chapman