Ringworm is self-limiting, and it can heal on its own, but it can often take one to six months or even longer for the lesions to heal. During that period, the affected horse can spread the fungus and infect many other horses in the herd, so it’s worthwhile to be proactive in calling your veterinarian, diagnosing the problem and treating it as early as possible.
Ringworm is a disease of the skin and hair, and contrary to its name, it’s caused by a fungus rather than worms. In North America, various species of two genera – Microsporum and Trichophyton – are the most common sources of infection in horses. These fungi can also infect small animals and other livestock. Ringworm is also a zoonotic disease, meaning that it can be transmitted from animals to humans.
Ringworm is spread through direct contact between infected animals, as well as by fungal spores found in the environment. The spores can be found on tack, brushes and other equipment. They are very resilient, and can survive in an environment for many years. Horses that are most commonly affected by ringworm include young animals under three years old and those that have compromised immune systems from disease or poor nutrition. Healthy adult horses can also contract the fungus, however.