Oh no, the dreaded ringworm season is here! When we suspect ringworm in a pet, or more often, as part of a general skin workup, hair samples are collected by plucking or using a new toothbrush to brush the animal’s coat. The hairs are then placed in culture medium for about 10-14 days. With ringworm, the medium typically turns shocking pink (from dull orange) at the same time that fungal growth occurs. Growth without color change is typically due to nonpathogenic fungi. Confirmation is achieved on microscopy by finding rowboat or cigar-shaped chambered macroconidia on the ends of filamentous growth, using new methylene blue stain.
Treatment is prolonged as with any fungal condition. Topical and systemic treatment are usually recommended. Topical dips include lime sulfur or miconazole + chlorhexidine. Systemic treatments include ketoconazole in dogs, itraconazole in cats, fluconazole, or griseofulvin. All of these medications have the potential for severe side effects, such as bone marrow toxicity or hepatotoxicity. Household surfaces are cleaned with bleach and multiple pets in the household may need to be treated, especially cats.
Ringworm is zoonotic, so if a pet is being treated for ringworm, and a person in the house develops a rash, they should see their physician.