Not all dogs that come in contact with ringworm will show signs of an infection. Ringworm infections depend on the type of fungus, as well as the dog's age, relative health, nutrition and grooming.
Any dog can develop a ringworm infection, however, certain age ranges and breeds are more at risk. In an article for DVM360, veterinary dermatologist Anthea Schick says Boston terriers, Yorkies and Jack Russell terriers are all prone to contracting ringworm. Very old dogs, puppies and dogs who have a suppressed immune system, she continues, are at an increased risk for developing ringworm.
Dogs with ringworm are contagious to humans. If your dog has been diagnosed, or if you suspect they may have ringworm, do not handle them and then directly touch your skin. Wash your hands after every touch, and if you notice any red, circular itchy spots on your own skin, call your doctor.