Ringworm (dermatophytosis) is not actually a worm, it’s a fungal infection that can affect the hair, skin or nails of both cats and dogs, and humans. The most contagious skin infection in cats, it can easily be transmitted from cats and dogs to other animals, and also to, and from, people.
Several different fungi can cause ringworm but the vast majority of cases in cats and dogs are caused by Microsporum canis, Microsporum gypseum or Trichophyton species. The fungus is commonly found in soil and often affects gardeners, who can transmit it to their pets. Once infected, an animal will shed spores into their living quarters, on brushes, bedding, furniture, or anything that has been in contact with an infected animal, and into the wider environment. Humid, warm environments encourage growth of the fungus.
Cats can be asymptomatic carriers, carrying the fungus but showing no signs of the infection themselves, and transmitting the fungi to any other pets they come in contact with. Animals thought to be chronic carriers can be routinely cultured to determine if they are carriers. Where a cat is confirmed as a carrier, if you have other pets in your home, the only way to minimise the spread of ringworm through all of your pets is by ensuring that the carrier cat is permanently kept outside.
Because ringworm spores can survive for long periods in the environment your cat can contract ringworm from just about anywhere other dogs or cats have been. Fortunately, most healthy adult cats have a degree of natural resistance to ringworm and never develop symptoms from the fungus. Young cats under a year old are most often infected. Older cats with a suppressed immune system caused by disease are also more susceptible to contracting the disease. Senior cats, free-roaming cats, and those under stress, malnourished or suffering other diseases such as parasites or viral infections are also at increased risk.
The classic symptom of a cat infected with ringworm is a small circular lesion, or spot, that is red, hairless, and often scaly in the centre. Small pustules are often also found in the lesion, which are most common on the head, ears, and tail. In some infections the fungus will not be in a circle and can spread across the face, lips, chin, or nose and look like an autoimmune disease or other generalised skin disease.
Hair loss may be mild or severe. In some cases the first sign may be excessive shedding, and hairballs may occur when large parts of the body are affected. Scratching at the ears is also common. Ringworm can also occur in the nails, often causing them to grow malformed.
How is ringworm diagnosed?
Ringworm can most easily be diagnosed by looking at a lesion under a UV lamp. The infection will glow a fluorescent color when exposed to UV light. However, not all the species of the fungus will fluoresce. A healthy animal may have spores on his or her coat that fluoresce, but not have an active infection.
If there is any doubt we will confirm, or eliminate, a ringworm infection by collecting scales and crust from the skin and coat and performing a fungal culture, but in most cases an infection is fairly easy to identify.
Treatment is relatively simple. A fungal shampoo such as F10 or Malaseb, together with the application of a fungal cream will generally quickly clear up the infection.
Some cases of ringworm are more resistant to treatment and will also require the use of an oral antifungal medication.
Because the ringworm fungus can survive for such long periods in the environment, and be transmitted to or by humans, one of the most important elements of treatment, and the prevention of future infections, is hygiene. It is important that you thoroughly wash your hands after treating your pet, and after playing with it. You should also thoroughly clean wherever an infected animal has been to eliminate the spores.
Spores are very light and are carried in the air so wherever there is dust and hair, there may be spores. Vacuum and mop hard floors, and steam clean carpets. All grooming tools, bedding, kennels, cat carriers, and cages should also be thoroughly cleaned and disinfected.
Ringworm is a disease where prevention is definitely better than cure. If you have cats, be very careful about bringing a new kitten into your household. Cat shows, kennels, and grooming facilities can also be a source of infection. Breeders of Persians and Himalayans need to be especially cautious about bringing any new animal that has not been cultured into their facility. If any sign of ringworm is seen, make sure you isolate the infected cat and call the hospital for advice.