Ringworm is the common name for a skin infection caused by one of several Dermatophyte fungi. The name is misleading as the infection has got nothing to do with worms. Ringworm fungi can cause infection in many types of animals, including people, cats and dogs. The disease tends to show as reddish, scaly rings on the skin of people. Some infected animals (especially young cats) may show no skin lesions at all and others will have patches of dry scaly skin or other types of skin change. Most lesions that look like the classic ringworm rings in animals are actually caused by Staphylococcus bacteria.
Ringworm can spread from animals to people, from people to animals and both can catch the infection from the soil. Fungal spores are shed from infected skin, where they can survive in the environment for months to years before causing infection. People and animals with a weaker immune system (they are young, old, sick or on certain medications) are at greater risk of developing a ringworm skin infection. Some animals are only diagnosed when a human member of the family develops a skin lesion.
Several different techniques can be used to try to diagnose a ringworm infection in animals. About 50% of the most common type of dermatophyte fungi will fluoresce under an ultraviolet light, so this is the easiest way to confirm an infection. If there is no fluorescence under a UV lamp, then other methods such as examination of a hair sample under the microscope (though the spores are very difficult to find) and fungal cultures (though this will often take 2 weeks) can be used to try to confirm the disease. In rare instances a skin biopsy may be the only way to diagnose the problem.