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.

How did my dog get ringworm?

Direct contact is the main mode of transmission of ringworm among dogs and in between dogs and other animals. Transmission often happens when a dog is in contact with the infected animal or any contaminated object like a carpet, food bowl, or bedding. Infected animals spread fungal spores into the environment when they shed off infected hair. Fungal spores can stay viable for up to 18 months.

However, contact alone is not enough to cause an infection in dogs and humans. Host factors like immunity, age, health condition, nutrition, and grooming behavior can influence and affect the risk of infection even with direct contact with the fungal spores. Also, infected animals that have recovered can develop some degree of resistance against dermatophytes that protect them against reinfection for a short time.

Signs of Ringworm Infection in Dogs

Dermatophytosis in dogs typically causes hair loss and itchiness. Lesions are often seen in bald patches, and the skin can become scaly and produce dandruff. The skin can also become darker and occasionally red from inflammation. Secondary bacterial infection may occur on the affected parts of the skin and pustular nodules may start to develop.

The commonly affected parts of the dog’s body are the feet, face, ears, and tail, as these are the ones that come in contact with various objects in the environment or other animals. The nails and nailbeds can also become infected, which can result in misshapen, broken, or brittle nails in dogs. Redness and darkly pigmented skin are often seen in dogs with ringworm infection on their nails and nailbeds.

Dogs can become carriers of dermatophytes, and not show any signs even if they are carrying the fungal organism. Asymptomatic carriers can still transfer the infection to other animals and humans through contact.

How is ringworm diagnosed in 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 link for 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)

Can ringworm infection be prevented?

Since ringworm is primarily transmitted through direct contact, isolation of the infected animal and daily cleaning of the house and objects that might have come in contact with an infected animal can help prevent transmission and control the spread of ringworm. Supplements that help improve your dog’s immune system and general health can help prevent infection even if there’s contact with infectious spores.

Recently, a vaccine is being studied that can offer protection against some species of dermatophytes that cause ringworm in dogs. Having your dog vaccinated can help offer protection but does not eliminate the risk entirely, since other fungal species can cause skin infection in dogs.

Read more:

How to Safely Manage Fleas in Pets

Ditch the Itch: Skin Allergies in Dogs

Deworming Your Dog - Q&A

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