Ringworm in Cats and Dogs - is it a worm?

17 Oct 2018

This summer we have been seeing more Ringworm cases in kittens than is usual. An understandably common misconception that many of our clients have is that ringworm is caused by a worm. 

Ringworm is actually a fungal infection which can affect the skin, hair and nails. The medical term for Ringworm is Dermatophytosis. 

The most commonly isolated fungal species are Microsporum canis (commonly referred to as Ringworm), Trichophyton mentagrophytes and Microsporum gypseum. Cats, dogs and other mammals including people can be affected. Ringworm is more common in puppies and kittens than adult cat and dogs.

These organisms are everywhere in our environment so like people, animals are exposed to these organisms from an early age. Pets can become infected from the environment, directly through contact with an infected animal or indirectly through contact with bedding, food bowls and other materials that have been contaminated with the skin cells or hairs of infected animals.  Ringworm spores are very tough and can survive in the environment for more than a year.

In normal circumstances as animals grow up their immune systems mount a defence against the organisms and the animal becomes resistant to infection.  Diseases or medications that weaken the immune system can increase the risk of disease as can environments that are densely populated with animals (e.g. an animal shelter/rescue centre, kennel, stray cat colony) or where there is poor nutrition and hygiene practices. Warm and humid conditions tend to promote Ringworm infections.

Symptoms of Ringworm can vary and can range from dandruff (scales) and poor hair coat (thinned and patchy looking) to scaly areas of hair loss with which can be circular or irregular in shape. The skin can be reddened or darkened. Some pets will itch while others don’t. Nodules or boils on the skin are less common. Affected nail beds may be red and inflamed.

What makes things more complicated is that not all animals infected with Ringworm have lesions.  We call these animals asymptomatic carriers. It is these animals that can make getting rid of Ringworm more difficult, as even though they don’t look sick they are contagious to other animals and humans.

Our first line test for diagnosis of Ringworm is a Woods Lamp examination of the hair.  This test is quick, easy and inexpensive and involves taking the animal into a darkened room and shining a special UV light on the hair and skin. Hairs that are infected will fluoresce a bright apple green colour confirming the diagnosis of fungal infection. Unfortunately we only pick up about sixty% of cases by this method so if we are suspicious that a pet has Ringworm or we need to rule it out when working up skin problem our next step is to pluck a sample of hairs and send them to the laboratory for examination under the microscope to check for fungal hyphae and spores and a Fungal Culture.  Fungal organisms are slow growing so it takes about three weeks to get culture results back. Very occasionally skin biopsies and histopathology are required for diagnosis.

Treatment is normally on an outpatient basis and involves use of anti-fungal medication and where possible clipping the hair from affected areas.  For localized lesions topical creams are useful. In more generalized cases often long courses of oral antifungal medication combined with antifungal shampoos are necessary (usually a minimum of thirty days).  Treatment is continued until the Woods Lamp examination or Fungal Culture is negative.

In contact pets will have invariably been exposed so should be examined for signs of Ringworm as well as being tested and if necessary treated.

There is a risk that you could catch Ringworm from your pet. The risk is higher in children, elderly people and in people with weakened immune systems.  If your pet has Ringworm it is important to practice good hygiene after handling such as hand washing and carefully observe for the development of suspicious skin lesions.  If you are concerned you should get these checked out by your doctor.

To reduce the risk of transmission to in contact pets and people in the household it is important to decontaminate the household environment as much as is possible. In practical term this means washing the infected pets bedding and toys with a disinfectant that kills ringworm spores (a 1:10 dilution of household bleach is effective) and discarding items that are impossible to thoroughly disinfect (e.g. scratch posts and carpeted cat towers). Because fungal organisms survive on shed hairs and skin cells/scale it is very important to thoroughly and frequently vacuum your house to get rid of the environmental build up.

If you are concerned that your cat or dog may have Ringworm or if someone in your household has ringworm and you would like your pets checked to see if they are infected please book an appointment to see us. 

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