Ringworm is a fungus, not a worm. How it spreads between dogs and people, how it is diagnosed, and how treatment and cleaning together clear a kennel.
Ringworm, or dermatophytosis, is a skin infection caused by fungi, most often Microsporum canis, Microsporum gypseum from soil or Trichophyton from rodents and their burrows. It spreads by direct contact and by spores shed with infected hairs, which survive for a year or more on brushes, bedding, crates and kennel floors. Puppies, old dogs and dogs with weakened immunity are most at risk. Ringworm also infects people, especially children, who get itchy, round red patches, so everyone in the household should know about it and see a doctor if they get symptoms.
Typical signs are round, hairless patches with scaling or crusts, often on the face, ears and front legs, but ringworm can look like almost any skin problem, and some dogs carry spores without visible lesions. Under a Wood's lamp some Microsporum infections glow apple green, but a negative result does not rule ringworm out. The vet confirms the diagnosis with a fungal culture or PCR of hairs brushed out with a new toothbrush. Because PCR also detects dead fungal material, cultures are used to show when a dog is cured.
Treatment combines medicine for the dog with cleaning of the environment. The vet usually prescribes an oral antifungal such as itraconazole or terbinafine, together with treatment of the whole coat, for example a shampoo with miconazole and chlorhexidine or lime sulphur dips twice a week. Clipping a long coat can help but should be done gently, since it spreads spores. Treat every dog that has been in contact, not only those with lesions, and continue until the vet confirms they are clear, usually with two negative cultures in a row. Stopping too early is the most common reason ringworm comes back.
Remove spores mechanically first: vacuum and wipe all surfaces, wash with detergent, then disinfect with a product proven to kill dermatophyte spores, such as diluted household bleach or accelerated hydrogen peroxide, following the label. Wash textiles twice at the highest temperature they tolerate and throw away what cannot be cleaned. Keep affected dogs in a room that is easy to clean. Pause matings, visits, sales and shows until the kennel is clear, tell buyers and other breeders honestly if they may have been exposed, and check new dogs before they meet your own.
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