Ringworm for "Dummies"...Nice and Simple

....this is a primer on the fundamental knowledge we have about Ringworm, pertaining to cause, mode of infection, risk factors, clinical signs, diagnosis, treatment, monitoring therapy, vaccination and control. Much more detail can be found in veterinary textbooks and journals. For more depth, the reader is referred to issues of the The Compendium of Continuing Education, published in November and December, 1995.1 Also, Veterinary Medicine, March 2003, pp216 and Veterinary Medicine October 2003, pp845. This author has created a fairly large (~30 page) downloadable Adobe Acrobat-formatted (.pdf) outline of four articles focused on the problem of Ringworm in cats. The original article was designed for veterinarians but is relevant and important to clients and their pets. The salient features are outlined in the pdf file for you. (If you have a pdf browser plugin installed, you will see the document open in a separate browser window ; you can then save the document to your hard drive.). PLEASE NOTE: the final version of the downloadable pdf file is still in preparation...only a preliminary draft is available now...


The common name, "ringworm", is somewhat confusing since the disease is NOT caused by a worm, but rather by one of several species of fungi. The medical term for infection is "dermatophytosis". Causative fungi are sometimes found as normal inhabitants of soil. However, more often than not, contaminated households, kennels and catteries readily serve as sources of infection, as decontamination of these areas can be extremely difficult. Some infections can be spread from a single animal to another animal or rarely, to a human. The disease itself has a very low mortality but in ill-thrifty animals, invasion of the compromised outer skin layers (see below) by other organisms is possible and severe illness may ensue. Ringworm is the most common infectious skin disease of cats.


Clinical signs result from penetration and digestion of the non-viable outer skin layer and of hair shafts by infective fungal elements. Often, there is some trauma to the skin, including bites from fleas, clipping wounds, etc. Arthrospores (the infective element) are present on the broken hairs, collars, and brushes from infected or carrier animals and contamination of the environment from these sources is common Arthrospores invade hair shafts and stratum corneum (the outer-most layer of the epidermis...see "SkinBasics" page).Some strains can also invade "living" tissue as well. Immune and inflammatory responses to organisms and their metabolic by-products contribute, in part, to the appearance of gross lesions (see below). In rare instances, an infected hair follicle may rupture and spread organisms to tissue beneath the skin (subcutaneous tissue) producing a firm, sometimes painful nodule known as a "pseudomycetoma". The disease is highly contagious, and Microsporum canis, the most common species in cats, is zoonotic, meaning that infections are transmissible to other species, including humans. (Not all dermatophyte species are transmitted between animals)

Risk Factors:

Risk factors for dermatophytosis ...at least in cats, which have been extensively studied... include very young and older animals and animals that are immunocompromised. Grooming inhibits development of infection, so animals which are not grooming are at increased risk, as well. Additionally, and quite significantly, long-haired cats are at considerably greater risk for infection and/or maintaining a reservoir of infectious elements (arthrospores). These "carrier" animals may actually show no clinical signs of disease! Finally, there may be genetic factors that predispose some cats to increased suseptibility.

Environmental factors also present risks. High humidity, favors arthorspore survival. Bathing of cats may remove naturally protective skin secretions (sebum and serum) which increases the probability of invasion and infection by fungal elements.

More details about risk factors and other circumstances favoring infection is described in the downloadable pdf file. (If you have a pdf browser plugin installed, you will see the document open in a separate browser window ; you can then save the document to your hard drive.)


Clinical Signs:

· In cats, Infection may present with any combination of the following


Considerably more details, including pictures of diagnotic methods, findings and interpretations can be seen in a downloadable pdf file. (If you have a pdf browser plugin installed, you will see the document open in a separate browser window; you can then save the document to your hard drive).


Monitoring Therapy:

Beginning four weeks, after the onset of treatment, repeat fungal cultures should be performed. These should be repeated at two to four week intervals until negative cultures are obtained. Then culture weekly and treat for additional period until two to three negative cultures in a row are obtained.

Do not allow cats to go outside, and culture any new cats prior to allowing entry into the environment.

Discard any potentially contaminated items in contact with affected cats, vacuum thoroughly and often and discard contaminated vacuum bags immediately. Scrub and disinfect surfaces tolerating potent disinfectants, such as bleach. Make sure to disinfect (or change) shoes so as not to tract potential fungal spores into the environment.

More information on monitoring and maintaining a fungal-free cat house-hold can be found here: (Outline of Dermatophytosis)




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