Contact your veterinarian. A low immune system makes humans and cats more susceptible to ringworm, says Dr. William Fortney, Kansas State University veterinarian. Ringworm, which is actually a fungus and not a worm, is predominately a cat disease. There are many kinds of ringworm, but only one is shared between humans and cats.
Humans can also get other kinds of ringworm from the environment.
Fortney says it is generally a young animal disease because of their low immune system. A strong immune system prevents contraction of ringworm, or at least limits it so not much treatment is needed if the fungus is contracted. Ringworms are dermatophytes, which means they like skin and don't go any further than that. In cats, ringworm will cause a crusty, circular lesion and the hair falls out. The lesion doesn't have to be circular and there are other things that cause circular lesions.