Ringworm

Veterinary advice should be sought before applying any treatment or vaccine.

Ringworm

Dermatophytosis, Girth Itch, Jockey Itch, Athletes Foot, Onycomycosis, Epidermophytosis

Ringworm is a superficial, highly contagious skin infection caused by a closely related group of fungi known as dermatophytes. Dermatophytes have the ability to utilize keratin as a nutrient source (i.e. they have a unique enzymatic capacity [keratinase]). There are several different species and strains of dermatophytes, therefore the type and severity of the infection differs from horse to horse. Some dermatophyte species are zoophilic, meaning they are able to cause infections not only in horses, but also humans or other animals. Certain animal species are more prone to infection by a particular dermatophyte species. In horses, recent studies have found that each species of dermatophyte tends to invade a particular area of the horse and cause their own specific reaction.
SpeciesNatural HabitatWhere found on horsesClinical signs
Microsporum canisCatsGeneralized, saddle areaMultiple areas of hair loss
M. equinumHumans, HorsesSaddle, flank and girth areas (pressure areas)Discrete, raised areas of crusting, progressing to areas of patchy hair loss
M. fulvumHumansHeadArea of hair loss
M. gallinaeChickensFlank and girthCircular area of hair loss
M. gypseumSoil/Dead animalsLimbs and saddle areaLesions
Trichophyton equinumHorsesSaddle areaSingle area of pathy hair loss
T. mentagrophytesRodentsLimbsLesions
T. soudanenseHumansGirth areaAreas of hyperkeratosis and patchy hair loss
T. vanbreuseghemii GeneralizedAreas of hair loss ("moth eaten" appearance)
T. verrucosumCattleLimbs and rumpAreas of inflammation
Although ringworm can occur in horses worldwide, it is more prevalent in hot, humid climates than in cold, dry regions.

Dermatophytes produce enzymes called keratinases that break down the protective barriers of the outer layer of the horse's skin and hair, allowing itself entry to establish infection.

Ringworm is characterized by the appearance of circular areas of hair loss, scaling, and crusting. Although in can occur anywhere on the horse's body, it most often occurs on the face, legs, girth, shoulder, and chest.

Transmission
Ringworm is easily transmitted, and occurs through direct or indirect contact with skin of other infected animals, insects, people, soil or fomites (tack, blankets, grooming equipment, etc.). The fungus has been known to survive on saddle-girths for 12 months.

Incubation period
The incubation period for ringworm varies from several days to a couple weeks.

Symptoms

Round, hairless skin lesions
Crusting and scaling
Areas of hair loss
Skin greyish white in color
Lesions found in the girth or saddle area

Diagnosis

  • History
  • Clinical signs
  • Physical exam
  • Fungal skin culture

Treatment


Topical therapy : 2% lime sulfur

Prevention

  • Biosecurity
  • Maintaining a well balanced diet
  • Don't share equipment, tack, blankets, etc. with different horse owners or horses
  • Reduce stress

Scientific Research References

Good Overviews

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Risk Factors

  • Lowered immune system
  • Concurrent illness
  • Stress
  • Existing injury or skin condition such as abrasions, excessive dry skin or allergic reactions
  • Younger horses, under 3 years of age
  • Prolonged moisture exposure

Seasonality

WinterSpringSummerAutumn