Microsporum ringworm, a fungus that causes a skin infection called ringworm, can pass from animals to people. It is characterized by skin lesions and small scaly patches that do not always form a circle, microsporum ringworm causes hair loss at the affected site. Ringworm mimics other skin infections, such as demodex, caused by a parasite. Seventeen species of Microsporum exist.

Pathogenic dermatophytes are parasitic fungi that share the ability to invade keratinized (do not have circulation, technically dead) structures such as hair, nails, and stratum corneum, causing superficial infections called dermatophytosis in both humans and animals. Microsporum canis is the main agent of dermatophytosis in dogs and cats but is also a frequent zoonotic agent, as shown by the increasing prevalence of human infections in many European countries.

Human infection occurs mainly by direct contact with infected cats, which are considered the natural hosts and the reservoir for Microsporum. The fact that cats can be asymptomatically infected (no sign of infection) enhances the risk for both human and animal contamination since they are responsible for occult and massive dissemination of fungal material into their environment.