Fungal Skin Infection in Dogs
Ringworm and yeast are different problems with different treatments. How to tell them apart, and which one transmits to people.
Two quite different things are grouped under fungal skin infection in dogs, and they need distinguishing because the treatment and the risk to people differ.
Ringworm
Ringworm is not a worm. It is a fungal infection of the hair and skin, most often caused by Microsporum canis.
What it looks like: circular patches of hair loss, often with scaling and a crusty edge, commonly on the face, ears, paws and tail. It is frequently not very itchy, which surprises owners.
It transmits to people, and to other animals. Children are most susceptible. If someone in the household has developed a circular red itchy rash, mention it.
Diagnosis is by fungal culture, by examining plucked hairs under the microscope, or by PCR. An ultraviolet lamp makes some strains fluoresce, but a negative result does not rule it out.
Treatment takes weeks: antifungal medication by mouth, topical treatment or medicated bathing, and thorough decontamination of the environment, since spores persist in bedding and carpets for a long time. Treat every animal in the household.
Do not stop treatment when the skin looks better. It is stopped on the basis of repeat cultures, not appearance.
Yeast
Malassezia is a yeast that lives normally on dog skin and overgrows when conditions favour it: warmth, moisture, and above all an underlying allergy.
What it looks like: greasy, red, thickened skin with a distinctive musty smell, and intense itching. It concentrates in the warm folds: ears, between the toes, armpits, groin, neck folds and around the lips.
Brown staining between the toes from constant licking is a very common sign.
It does not transmit to people.
Treatment is antifungal shampoo and topical treatment, medication by mouth in more severe cases, and, critically, addressing the underlying cause. Yeast overgrowth is almost always secondary to allergy, and treating the yeast alone means it returns within weeks.
Telling them apart
Ringworm: circular patches, hair loss, scaling, often not very itchy, transmits to people.
Yeast: greasy red skin in the folds, musty smell, intensely itchy, does not transmit to people, and there is usually an allergy underneath.
They look different once you know what to look for, but neither should be guessed at. Both are diagnosed with simple tests at the clinic.
What not to do
Do not use human antifungal creams without advice. Do not use tea tree oil, which is toxic to dogs. Do not bathe repeatedly with ordinary shampoo, which strips the skin and makes it worse.
When to come in
Circular patches of hair loss. Greasy, smelly, itchy skin in the folds. Brown staining between the toes. Recurrent ear infections. And promptly if anyone in the household has developed a rash.