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Understanding and Managing Ringworm in Dogs and Cats

Ringworm, or dermatophytosis, is a common fungal infection that affects both dogs and cats. It is particularly challenging to manage in environments with many animals, such as shelters, due to its long incubation period and high transmission rate. Here's a comprehensive guide on what ringworm is, how to diagnose it, and effective ways to treat and prevent it.

What is Ringworm?

Ringworm is caused by fungal species such as Microsporum canis, M. gypseum, and Trichophyton spp. It is particularly troublesome in cats, which can carry spores for long periods. Although ringworm thrives in warm, moist climates, pets in any environment can be affected. The fungal spores are microscopic and can live on an animal’s hair and in the environment for up to two years, making them highly contagious.

Identifying Ringworm in Pets

Ringworm presents as small, round lesions causing patchy hair loss. These lesions are typically not itchy, causing minimal discomfort. Young animals may exhibit more widespread infections, while older animals have localized spots. Infected kittens often have lesions on their face, ears, and front legs, while dogs, particularly puppies, show more typical ringworm lesions. In adult dogs, similar lesions might be due to mange or bacterial infections.

Diagnosing Ringworm

Several methods can be used to diagnose ringworm in pets:

  1. Fungal Culture: Collect a hair sample from the infected area and place it in a test medium to grow the fungus. Results can take one to two weeks.

  2. Woods Lamp: Use a black light to detect M. canis, which fluoresces under ultraviolet light. Note that other substances, like iodine, can also fluoresce.

  3. PCR Test: This test identifies the genetic material of the fungus in the skin and hair.

  4. Skin Biopsy: A more invasive method where a sample of skin is surgically removed for examination.

Treating Ringworm

Effective treatment of ringworm requires a combination of topical and oral medications:

  1. Topical Treatments:

  • Lime Sulfur Dip: This is highly effective for eliminating the infection and reducing environmental contamination. It’s suitable for use on nursing queens and kittens as young as four weeks. Ensure the animals are kept warm until dry, and wipe the dip off mammary glands before allowing nursing.

  • Antifungal Sprays: These can be applied to new spots immediately to stop further transmission and treat current infections after bathing or dipping.

  1. Oral Treatments:

  • Itraconazole: Safe for dogs and cats, administered orally at 5 mg/lb daily for 21 days.

  • Terbinafine: Safe with few side effects, dosed at 20–30 mg/kg daily until the infection is cured.

  • Ketoconazole: Effective and safe for dogs but not recommended for oral use in cats. Used at 5 mg/lb daily until cured.

  • Griseofulvin: Used less frequently due to safety concerns, especially in cats.

Environmental Management

Ringworm spores are resilient and can be present almost anywhere. Here are key steps for managing the environment:

  • Vacuum Frequently: Remove spores from carpets, furniture, and other fabrics, and dispose of vacuum bags immediately.

  • Disinfect Thoroughly: Use disinfectants that kill fungal spores for all bedding, laundry, cages, and equipment.

  • Use Chlorhexidine: This disinfectant is effective against ringworm and safe for use around nursing animals.

Preventing Ringworm

Preventing ringworm involves maintaining a clean environment and good hygiene practices. Bath pregnant animals before birth to prevent transmission to newborns. Using disinfectants like Chlorhexidine in the nest box can help eliminate spores. Regularly fogging areas with Oxine, Rescue, or Virkon can also reduce spore presence.

For more information and tips on managing pet health, visit

Understanding and Managing Ringworm in Dogs and Cats
Understanding and Managing Ringworm in Dogs and Cats


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