Ringworm is a common fungal infection of hair, skin and nails. In cats, Microsporum canis is the fungus causing approximately 90% of ringworm cases. Ringworm is rapidly spread in shelters and persists in the environment, and is therefore difficult to control and may be transmitted to caretakers and owners. Treatment options for ringworm are limited and difficult to administer, especially in outbreak situations. Though M. canis infection is widespread, and poses a risk of zoonotic infection to owners and veterinary staff, few studies have evaluated genetic aspects of this agent that relate to disease-causing potential. Understanding genetic characteristics of this fungus could help manage outbreak situations if isolates vary in virulence. Further, current treatment protocols are difficult and may be expensive and ineffective; therefore, assessment of new therapeutic targets are needed. This application proposes to use modern molecular tools to extend our preliminary studies to advance understanding about the ways M. canis can cause disease. This work will determine if variations in M. canis genes relate to differences in disease-causing potential, and will assess the activity two candidate genes that may be vulnerable targets for new therapies to treat ringworm infections.