Onychomycosis in white line disease in horses: pathology, mycology and clinical features

Abstract

Summary This paper describes onychomycosis in horses and reports the pathological findings, associated fungi and incidence of concurrent white line disease. In addition to these observations, relevance between post mortem and clinical findings of onychomycosis are discussed in 3 necropsied horses. Samples were collected from 100 hooves from a total of 51 Thoroughbreds suffering from white line disease. Of these, 15 hooves from 13 horses were also complicated with severe hoof wall fissure formation. Preparations from the same samples were used both for histopathology and for culture to identify the associated fungi. Onychomycosis was diagnosed when it could be confirmed histologically. Fungal identification was based on morphological characteristics in culture and the associated fungi were determined by comparison with culture morphology. As a result, 10 samples collected from horses were diagnosed as suffering from onychomycosis. Seven of these showed complicating severe inner hoof wall fissures and the soil fungus Scedosporium apiospermum or the teleomorph of this fungus, i.e., Pseudallescheria boydii, was isolated. The fungus was found to be ubiquitous in the fissure cavities, the terminal horn of the white line and the terminal horn‐like laminae of the metaplastic white line‐like tissue. It can be concluded that onychomycosis frequently causes white line disease and/or makes it worse. Associated with deterioration of the submural condition, the main associated fungus for onychomycosis in this series, was Genus Scedosporium and the most susceptible region was the terminal horn of the hypertrophied white line and/or the terminal horn‐like laminae of the metaplastic white line‐like tissue.

Ultrasonography of a ureteral and bladder fungal granuloma caused byScedosporium apiospermumin a basset hound

“…There is little information available about eumycotic mycetoma formation related to Scedosporium species. Scedosporium infection in other animal species has been documented including cats, horses, layer pullets, cows, and humans . In dogs, Scedosporium species have been previously documented causing keratomycosis, discospondylitis, osteomyelitis, disseminated disease, and rhinitis .…”

Scanning electron microscopy and fungal culture of hoof horn from horses suffering from onychomycosis

“…Poor hoof horn quality is therefore a major cause of reduced performance and lameness. Equine onychomycosis has become a recognised cause of poor horn quality and hoof horn disease 4–8 . Recent research 13,14 has confirmed that both dermatophytes, which are well known to infect skin and associated structures in humans and other species, and moulds exhibit keratinopathogenic activity.…”

“…In the last two decades, fungal infection has been associated with poor quality hooves and several hoof diseases 4–8 . The horn defects in horses suffering from equine onychomycosis range from brittle hooves with sand cracks, horn fissures and large crumbling areas around the nail holes 4,7,8 to severe cases of white line disease 5,6 …”

“…Several groups of fungi that cause infections of keratinised tissues in humans 9–11 and other species have been identified 8,12 . Dermatophytes commonly infect skin and associated structures, but a number of other moulds also seem to be of major importance in equine onychomycosis 4,6,8,13,14 . In vitro studies have shown that the mould Scopulariopsis brevicaulis can be pathogenic in equine keratinised tissues 13,14 …”

New methods for isolation of keratolytic bacteria inducing intractable hoof wall cavity (<i>Gidoh</i>) in a horse; double screening procedures of the horn powder agar-translucency test and horn zymography

“…Many direct or supporting lines of evidence have indicated that possible contributors to the formation of the Gidoh include decreasing toughness of the wall based on abnormal anatomical conformation of the foot [2, 18], swelling and softening of the horny structure by water and/or urine [6,7,8,9, 19], neglect of incipient lesions relating to irregular farriery [2], and infection of the wall by microorganisms [1, 2, 4, 5, 12, 13, 15,16,17, 19]. Scientific research data have shown that keratinopathogenic fungi can invade into, and proliferate in, horny structures of the foot [1, 15, 17]. This can result in the collapse of the hoof capsule due to the production of keratolytic enzymes [1, 12].…”