Ringworm

Information About Dermatophytosis AKA Ringworm

What is Ringworm?
“Ringworm,” or dermatophytosis, is a fungal infection infecting the skin, hair and occasionally nails of animals (and people). Three species of ringworm fungus most commonly affect cats and dogs. Microsporum canis, Trichophyton mentagrophytes and Microsporum gypseum.

How is it Transmitted?
T. mentagrophytes is thought to be contracted from exposure to rodent nests, and M. gypseum from contaminated soil, though the potential also exists for spread from animal to animal in a contaminated environment. M. canis is most often spread from contact with an infected animal or contaminated environment, and therefore is by far the most likely to be a serious problem in a shelter environment. Ringworm is very durable in the environment. Ringworm can persist in carriers, furniture, carpets, dust, heating vents, furnace filters and the like, and can infect animals housed in a contaminated environment months and even years later. It can be spread readily on grooming implements, contaminated toys and bedding, or by humans on clothing and hands. It can be found on the hair of animals from a contaminated environment even when the animal itself is not showing any signs. In nature, the incubation period for ringworm is between 4 days and 4 weeks.

What are the Signs?
The name “ringworm” comes from the most common appearance of a circular area of hair loss and scaling. The most common locations include the face, ears, feet and tail. However, ringworm can present with a wide range of appearances, including large areas of hair loss with or without crusts and exudate. Ringworm can cause infection of the toe nails and nail beds. Ringworm may either resemble or secondarily infect conditions such as “stud tail” and “chin acne” in cats: especially consider ringworm as a possible cause of these conditions if the cat is known to have been recently exposed. Ringworm lesions may or may not be itchy. Diagnosis is deduced using some or all of the following methods: Wood’s lamp (ultraviolet light with specific wavelength that causes the lesions to phosphoresce), direct microscopic examination, and fungal culture. All of these tests can produce a false negative. To be certain of a diagnosis of ringworm, it is imperative to microscopically examine and positively identify the fungus.

Which Animals Get it?
Animals of any age are susceptible, but young animals (<1 yr old) and geriatric animals are at the highest risk. Persian cats and Yorkshire Terriers as well as long haired cats in general may be at higher risk. Conditions that compromise the immune system such as FIV, FeLV, pregnancy/lactation, malnutrition, or anti-inflammatory drugs, cancer, and stress will also increase the risk of contraction. Also, animals with preexisting skin conditions are at an increased risk for contracting ringworm.

How is Ringworm Treated?
In most cases, animals spontaneously recover from ringworm within about 3 months. Awaiting self-cure is certainly a reasonable choice in a one animal household where contagion is not a major concern. However, in a shelter environment or foster situation, a more rapid resolution is often desirable. Treatment should be directed towards speeding recovery and reducing environmental contamination. Clipping the animal’s hair is often un-necessary in short/medium haired animals and may even worsen lesions through microtrauma and mechanical spread of spores. However, clipping is indicated for seriously long haired animals and those that may be unable to groom due to conformation, concurrent severe upper respiratory congestion, or matted coat. Topical dips and shampoos, although, generally recommended as an adjunct to systemic therapy rather than a sole treatment is important in a shelter situation because it reduces shedding of infections spores into the environment. Treatment with creams and ointments is ineffective on animals (they do not work on haired skin). 8% Lime-sulfur dip is readily available, safe, and most importantly, has been demonstrated to be effective in a shelter environment. It should be used twice weekly on affected animals. Systemic treatment is an important adjunct to topical therapy. The drawbacks are the relatively high cost of the drugs, the possibility of toxic side effects and the relatively long course of treatment required. These drugs include Griseofulvin and Fluconazole which are both anti-fungal medications.

How is Ringworm Prevented?
There is currently no vaccination available that is protective against ringworm. The best protection, as with many infectious conditions, is to practice excellent husbandry. Screening high risk animals before housing them with the rest of the colony will help identify potential issues. Cleaning contaminated areas with a 1:10 bleach solution as well as disposal of linens is recommended. Segregation of infected animals for the 4 day to 4 week incubation period before re-introducing them to the “colony” will catch and prevent some but not all cases.

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