What is Ringworm, and how do pets get it?

Question: What is Ringworm, and how do pets get it?

Ringworm derives its name from the classic red, round "worm like" lesion seen on human skin that is infected. It is not a worm though; it is a fungus that is spread from animals to humans.

Answer: Dermatophytosis is the medical term for "fungal infection of the skin, hair or claws" (keratinized tissue). Ringworm is not a worm, it is a fungus that can infect the skin of animals and humans. Some species of dermatophyte fungi live in the soil, some are adapted to humans, and some are adapted to animals, with worldwide distribution. The animal dematophytes are the ones known as "ringworm". Because it is transmissible to humans from animals, it is also known as a zoonotic disease.

Ringworm is spread by contact with infected animals, and by touching objects that the infected animal has touched; such as bedding, brushes or grooming equipment, saddles and other tack, furniture, rugs, etc. Not every animal or human who touches infected animals or objects will become infected; the age, immune status, skin condition and grooming habits of the recipient influence if the fungus is actually able to grow and infect.

In animals, the classic Ringworm lesions are patchy areas of hair loss and scaliness, usually with very little inflammation or redness. It is not usually itchy.

Ringworm is best diagnosed by doing a fungal culture -- adding some hair and skin scraping material to a tube of growth media (culture) and seeing what grows on it. This can take several days to a few weeks. A quick "in office" test is the Wood's lamp test, using an ultraviolet (black) light in a darkened room to see if the affected area will fluoresce to a yellow-green. It should be noted that not all ringworm fungus infections will fluoresce, and other (non Ringworm) skin infections will not fluoresce at all.

Most animals will "outgrow" the Ringworm fungus as their body's immune system fights it off over the course of a few weeks. Animals that are immunocompromised or very young or old will have a more difficult time. One caution with an infected animal is the potential to spread the fungus to other animals, humans, or contaminate the environment. Topical medications vary in effectiveness. Oral medications are generally reserved for severe and/or chronic infections and can be expensive and with side effects. Please speak to your veterinarian about what treatment is best for your pet's condition, age, and general health status.

Reference: Merck Veterinary Manual, 9th ed.