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y a variety of fungal metabolites. T equinum produces urease, gelatinase, protease,
hemolysins, keratinases and lipases. Trichophyton spp
have been shown to produce proteolytic enzymes capable of inducing acantholysis.
As well as pro-inflammatory metabolites T. mentagrophytes produces mannans that
may inhibit T cell responses and reduce epidermal turnover (exfoliation being an
innate defence mechanism of the skin to surface microbes). Concurrent bacterial
infection is sometimes seen in dermatophytosis and dermatophytes may liberate
penicillin-like substances that result in the formation of penicillin resistant bacteria
from affected skin.
There seems to be a lack of specific immunological studies in the equine however
based on other species it would appear that spontaneous resolution is associated
with the development of cell mediated immunity (IFNγ and IL2). There does not
appear to be any correlation with antibody titres. Recovered horses from T equinum
and M. gypseum infections are reported to be resistant to re-infection with
dermatophytes of the same species.
Clinical features:
Dermatophytosis is a follicular infection so the common clinical symptom is of
folliculitis. This may include hive like follicular tufts, annular, peripherally expanding
areas of alopecia with variable scaling or crusting, classical ring lesion with peripheral
papules, coalescing areas forming serpiginous patterns of alopecia, exudative lesions
on the caudal fetlocks “grease heal” and rarely subcutaneous and dermal nodules
(dermatophytic pseudomycetoma). Pruritus is minimal or absent unless complicated
by ectoparasites and pain is uncommon unless complicated by Staphylococcal
folliculitis.
Lesions in dermatophytosis are most commonly seen on the face, neck, dorsolateral
thorax and the girth area. It has been reported that dermatophytosis affecting the
girth is most likely to be T equinum (fomite transmission) and that M. gypseum is most
commonly isolated from face, neck, legs and rump (geophylic fungus spread via
arthropods). T verrucosum is reported to have a thicker, grayish crust. Due to clinical
overlap, lesion type and location should not be relied on to identify species of
dermatophyte involved.
Zoonotic factors:
T equinum, T. verrucosum and M. canis all have zoonotic potential
Differential diagnoses:
Other folliculitides
- Staphylococcal folliculitis
- Dermatophilosis
- Pemphigus foliaceous
- Eosinophilic folliculitis
ACVSC Proceedings Dermatology Chapter Science Week 2005 107