Ringworm in Cats and Dogs
Does your pet have ringworm? What can you do to help? Keep reading to learn about the different types and treatments of ringworm in cats and dogs.
This article was written by a FirstVet vet
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What is Ringworm?
Ringworm is not a worm! Actually, it’s an infection caused by a type of fungus. These are also called dermatophytes. A “ringworm” infection is also known as “dermatophytosis”, and it can infect many animals including dogs, cats, and people. Several species of fungi can cause infection in the superficial layers of skin, and also hair and nails.
The most common dermatophytes causing infection in dogs and cats:
- Microsporum canis (prefers living on cats, dogs, sometimes large animals)
- Microsporum gypseum (prefers living in soil)
- Trichophyton mentagrophytes, T. verrucosum, and T. erinacei (affects hedgehogs)
Who gets it?
Ringworm tends to affect the young, old, and immunocompromised. A healthy adult animal may come into contact with these organisms without becoming infected by them. Most pets become infected through contact with other animals. It is not uncommon to see dermatophytosis in puppies and kittens, rescue and shelter pets or overcrowding situations, as well as hunting dogs or animals in warm environments. Animals that are under stress, malnourished, or harboring an underlying disease may be more likely to become infected. Interestingly, cats with FIV or Feline Leukemia are not more susceptible to dermatophytosis.
Dermatophytosis is a zoonotic infection, meaning humans can become infected by contact with infected animals. The name ‘ringworm’ comes from its red, round appearance surrounded by a scaly ring (on human skin).
How do animals and people become infected?
A combination of moisture on the skin, fungal spores, and microtrauma to the superficial layers of the skin can cause a lesion. The severity of lesions is correlated with immune response. There are no “more virulent” or “less virulent” strains, the infection is dictated by the host’s immune system. Many things can cause micro-abrasions to the skin, such as grooming and bathing, fleas, and mites.
Signs of Ringworm Infection in Pets
Clinical signs can be variable, from none to affecting the entire body.
- Asymptomatic (some animals show no clinical signs and you never even know they are infected)
- Hair loss (alopecia), often patchy, often starts around the face and paws but can affect any part of the body
- Scaling, scabs, redness, crusts, pustules, darker pigment of skin, and itchiness of the superficial skin layer
How is ringworm diagnosed in cats and dogs?
Diagnosis by your veterinarian may be immediate or take some time for testing through a laboratory. Tests for ringworm include:
- Wood’s Lamp - “apple-green” fluorescence under a black light of M. canis lesions (only) on a freshly plucked hair sample or on the pet itself
- KOH – Potassium Hydroxide, when heated, dissolves keratin and enables visualization of fungal spores under the microscope for specific species identification
- Culture – a sample of hair/crusts grown on a test medium to determine exactly which species of dermatophyte is present (or if any at all)
- PCR – tests for the DNA of the dermatophytes
- M. canis is most often the cause of dermatophyte infection in dogs
- M. gypseum is more common in humid, tropical regions
- M. gypseum and M. Trichophyton are the two dermatophytes found to be most commonly involved in combined infections, which can happen in dogs
Treatment of Ringworm in Cats and Dogs
Treatment requires persistent and appropriate medication, time, monitoring, and patience. Or doing absolutely nothing at all!
- Oral (systemic) and/or topical antifungal medication may be prescribed.
- Some animals may need periodic medicated baths and/or lime sulfur dips
- Fungal infections take longer to treat than bacterial infections
- You may have to continue medication for some time even after all lesions are cleared up
- Self-limiting infection - Some animals with healthy immune systems, a small amount of infection, or an already resolving infection at the time of diagnosis may rid themselves of the fungal infection without medical intervention. This should be determined by your vet.
Important Information for Humans:
- Ringworm is often easily treated in people (consult your physician)
- Follow this linkfor tips for decontaminating your home
- Preventing infection in others (animals and people):
- Keep your pet in the house until the infection is resolved (determine this with the help of your vet)
- Wash your hands after handling the pet
- Keep the pet away from all other pets in your home
- Don’t allow handling of the pet by people in your home (especially the young, old, and immunocompromised)
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