Ringworm" isthepopulartermforsuperficialfungal
infection oftheskin.IntheUKitistheonlyfungal
skin diseasethatisseencommonly.Thefungithat
cause skininfectionsinhorsesarecalled
dermatophytes andhencethecorrecttermfor
ringworm isdermatophytosis.Thetermringworm
presumably derivesfromthecharacteristicrings
that developwithinfection,howeverthetermis
misleading aswormsorparasitesarenot
responsible forthecondition.Thereare2generaof
dermatophytes thatmayinfecthorses; Microsporum
and Trichophyton. Ineachgeneratherearemultiple
species thatmayaffecthorseshoweverthevast
majority ofcasesarecausedbyonlyafewspecies.
Tricophytonequinum is themostcommoncauseof
dermatophytosis followedby Trichophyton
mentagrophytes, Tricophytonverrucosum,
Microsporum equinum and Microsporum gypseum.
Dermatophytes invadehairfollicleswheretheyfeed
on keratinandproducevastnumbersofpotentially
infective spores.Infectionusuallyrequiressome
existing disruptionoftheskinsurfacetoenable
penetration intothehairfollicle.Onceinfectionis
established itwillremainandspreaduntilthe
infected hairsceaseactivelygrowingoruntilan
immune responsedevelopsandthefungiare
eliminated. Theinfectionisalwaysself-limitingin
healthy animalsandeventuallyresolves.Following
infection clinicalsignsmaybeseenwithin1to6
weeks andthelesionsoftencontinuetoenlargefor
a fewmonthsbeforetheyeventuallyresolve.