Ringworm, also called dermatophytosis, is a fungal infection that occurs in the skin, hair and nails. The fungi feed on the keratin that is found in the outer layers of these structures. Ringworm infections can occur in all domesticated species of animals. There are a number of distinct species of dermatophyte fungi and some are ‘zoonotic’, meaning that they are capable of spreading from animals to humans.
The common name ‘ringworm’ is very old and is somewhat misleading, in that it is not an infection caused by a worm, and the infected areas are not always ring-shaped. In people, a ringworm infection usually starts as an itchy patch of skin that will expand outwards in a ring-like pattern. As it expands, the middle of the patch will heal while the edges will be inflamed and red.
In dogs, although the infection may sometimes look similar to the lesion in humans, more often the disease only causes one or more bald spots on the fur. In cats, a ringworm infection may appear as a patch of baldness, but more often the only symptom is some flaky dandruff.
Ringworm is contagious, and can be passed between animals or people by direct skin contact or by contact with contaminated objects such as combs, bedding, food bowls, furniture, or other environmental surfaces. Some animals and people can be “asymptomatic carriers” of ringworm, meaning that they have the fungus on their body but do not show any symptoms.
Contact with ringworm does not always mean that an infection will develop. The age of the exposed person or animal, whether they have other health problems or immune system disease, whether they have skin sensitivities or allergies, and what the level of exposure (the amount of environmental contamination that is present), are all important factors in the development of a ringworm infection. Young and old people and animals are more susceptible to ringworm infections.
Before assuming that a skin lesion is caused by ringworm, it is important to confirm the diagnosis by culture of the fungus in a laboratory, which includes determination of the specific species of ringworm causing the infection. A positive culture can sometimes be confirmed within a couple of days, but in many cases the ringworm spores may be slow to grow, meaning that it can take up to a month before a suspected sample is confirmed negative. A special type of ultraviolet lamp called a Wood’s lamp may cause some species of ringworm fungi to fluoresce, but this test is not always accurate. A Wood’s lamp test is sometimes used as a rapid screening test in multi-animal facilities, and suspect cases are then confirmed by culture.
Treatment of ringworm in animals is always necessary to avoid spread of the infection to children or other pets. Treatment of an individual pet will include a prescription of antifungal medication, combined with clipping or shaving the hair from the infected lesions to minimize further environmental contamination. In some cases, it is necessary to completely shave the animal’s fur. In minor cases, an antifungal cream, ointment or shampoo will be prescribed for topical application for a treatment period of several weeks to months. In the majority of cases, effective treatment requires the use of oral antifungal drugs for a minimum of six weeks. In all cases, the household must be thoroughly cleaned to eliminate any environmental source of re-infection. In a multi-animal environment, treatment can be extremely challenging and costly.
For further or more specific information about ringworm and your pet, please see our handouts on ringworm in the Pet Health Section of our website, or call us during business hours to speak with one of our health care team.
Caution: These news items, written by Lifelearn Inc., are licensed to this practice for the personal use of our clients. Any copying, printing or further distribution is prohibited without the express written permission of Lifelearn Inc. Please note that the news information presented here is NOT a substitute for a proper consultation and/or clinical examination of your pet by our clinic veterinarian.