Ringworm in Cats and Dogs

Cat with RingwormCat with Ringworm
Cat with RingwormCat with Ringworm

Table of Contents:

  1. The Basics
  2. Who’s at Risk?
  3. Methods for Diagnosis
  4. How to Treat Ringworm
  5. The Bottom Line

The Basics

Ringworm is a misnomer, since it is not actually a worm! This condition, also known as dermatophytosis, is a fungal infection of the nails, hair, and skin that affects both animals and people. Typically, skin lesions are in the form of a ring or circle, which may be the inspiration for its name. Similar to athlete’s foot, which is also a fungal infection, ringworm is spread by contact with an infected individual or a contaminated environment. Ringworm is also zoonotic, meaning it can spread between humans and animals.

Who’s at Risk?

Pets and people that are young, old, have compromised immune systems, or are sick are at higher risk of ringworm infections. Cats are most likely to carry and be infected with ringworm. In a shelter setting, this can be devastating, since treatment can take months and may discourage adopters. However, treatment for isolated pets in households typically takes less time and isn’t as urgent. Ringworm does not cause internal disease, but is more of an inconvenience, and should be avoided in immunosuppressed pets and people that may have trouble fighting the infection. Without treatment, pets often spontaneously recover from ringworm in approximately 3 months.

Dog with Ringworm

Methods for Diagnosis

  • Wood’s lamp
    • This is an ultraviolet light that can illuminate a specific species of ringworm.
    • The test is not exact and anywhere from 50-90% of strains will light up .
    • Other things like dry skin, nasal or ocular discharge, and lint may light up as well.
  • Microscopic evaluation
    • Typically, a few plucked hairs from the affected area are examined under a microscope.
    • This technique takes practice and should be used in conjunction with other testing to be sure of the diagnosis.
  • Polymerase chain reaction (PCR)
    • This is a fast and accurate test that takes 1-3 days to identify the presence of 3 different ringworm species from hair, nails, or skin scrapings.
    • The test does not give you the exact species of infection and may be cost prohibitive.
  • Dermatophyte test medium (DTM) culture
    • This is the “gold standard” of ringworm testing.
    • This test can take 1-3 weeks for a result.
    • Two negative cultures are required to consider an animal “cured.”

How to Treat Ringworm

Ringworm is most often treated based on veterinary speculation while waiting for test results, especially if lesions take on a classic appearance, which is hair loss in the shape of a circle, accompanied by dried, flaky skin. These areas are most commonly seen on the tips of ears, tail, or toes, but can be anywhere and may or may not be itchy. There are various anti-fungal shampoos, topical, and oral medications that can be used in combination for treatment. In the meantime, decontamination of your household to prevent spread or re-infection includes vacuuming and sanitizing surfaces, washing bedding and clothing in hot water, and discarding anything that cannot be decontaminated.

Ringworm on top of dog's head.
Overhead view of ringworm lesions.

The Bottom Line

Ringworm is more of a pain (or an itch) than it is a threat, but in homes with immunocompromised people, shelter settings, or a household with pets and kids coming and going, it is important to stay vigilant to prevent the spread of this pesky fungal infection.

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