found this on a website that I thought was interesting:
"Ringworm is not actually a worm, but is a fungal infection. Young horses are particularly at risk, but it can affect horses of any age. Initial symptoms include circular tufted areas of hair, about ½ inch in diameter; then the hair will fall out to reveal scaly skin which may become infected with pus.
Ringworm can spread very easily and the fungi can survive for at least a year in stalls, trailers, wooden fences, tack and grooming equipment. Anywhere that infected hair may reside is a potential source of contamination when another horse rubs against the infected hair. Ringworm is spread through the hair.
Treatment involves isolating affected horses, clipping all around infected areas (properly dispose of infected hair) and treat with any fungicidal dressing. You can also give anti-fungal meds in feed.
Use protective gloves when treating because it can occasionally be transferred to humans.
Disinfect all equipment, tack, wooden fences, trailers; anything that has been in contact with infected horsehair and or anything an equine might rub on. Use a power washer.
I have not had any ringworm in more than 15 years (knock on wood), so I cannot recommend any particular anti-fungal. There are many good anti-fungal products on the market today and I am sure any would suffice. Ask your veterinarian for a recommendation."