What kind of infection is it?
Ringworm infection is not caused by a worm at all - it's actually a skin infection caused by certain kinds of fungus called dermatophytes. The scientific name for ringworm is dermatophytosis.
The fungi feed upon the dead cells of skin and hair causing in people a classic round, red lesion with a ring of scale around the edges and normal recovering skin in the centre. The characteristic ring appearance is primarily a human phenomenon. In animals, ringworm frequently looks like a dry, grey, scaly patch but can also mimic any other skin lesion and have any appearance.
Where would my pet pick up this infection?
The spores of dermatophyte fungi are extremely hardy in the environment; they can live for years. They survive best in warm, humid environments. All it takes is skin contact with a spore to cause infection; however, the skin must be abraded as the fungus cannot infect healthy intact skin. This means that freshly shaved, scraped, or scratched skin is especially vulnerable.
Infected animals are continuously dropping spore-covered hairs as infected hairs break off into the environment. Some animals are carriers, who never show signs of skin irritation themselves but can infect others readily. Ringworm patients undergoing treatment commonly fit in this category towards the end of their care; the skin is still dropping spores but the visible signs of infection have cleared up. A carrier can also carry the spores on their fur without being infected, much as an inanimate object might have spores on its surface incidentally. In this situation, the spores can be easily washed away. There is no obvious way to distinguish between these two types of carrier state.
There are several species of dermatophyte fungi. Different species of fungi come from different kinds of animals or even from soil thus determining the ringworm species can help determine the source of the fungal infection.
Can I get this infection?
Yes, ringworm is contagious to people, however some people are at greater risk than others. Those with reduced immune capacity, such as young animals and children, elderly people and pets, people with immunosuppressive disease or people on chemotherapy, as well as highly stressed people and animals, are at greater risk.
The fungi are present in large numbers on hair and skin cells that are shed by infected individuals. People or animals can be infected through contact with infected hairs and skin cells, either directly on the affected person or animal (i.e. direct contact), or on things like clothing, blankets, hairbrushes etc. that have touched the affected skin (i.e. indirect contact).
How does your vet know this is really ringworm?
A fungal culture or a fungal PCR test is the only way to know for sure that the pet has dermatophyte fungi, in some cases we are only highly suspicious. Ringworm lesions on animal skin are rarely the classic ring-shaped as in people (in fact, in animals, lesions are often not even itchy) thus some testing is usually necessary. Some strains of dermatophyte fungi will glow under an ultraviolet light (woods lamp). If your vet sees a green fluorescence of the base of the hairs, they will be highly suspicious of ringworm. Not all strains of ringworm will glow and a culture or PCR is the only way to be sure of the diagnosis
Commitment is the key to success, especially if you have more than one pet. Infected animals are constantly shedding spores into the environment (your house) thus disinfection is just as important as treatment of the affected pet. The infected pet will require isolation in one room of the house that is easy to clean, while the environment is disinfected. Ideally all pets should be isolated until they have been deemed clear of infection, at which point they can be allowed back into the clean area. This is not always practical though, and more frequent cleaning and disinfection is required if the pets are not isolated.
Infected pets generally require oral medication, which is generally supplemented with topical treatment (shampoo, cream, or both). Localized lesions in dogs might get away with topical treatment only.
The problem with decontaminating the environment is that few products are effective. Bleach diluted 1:10 with water will kill 80% of fungal spores with one application and any surface that can be bleached should be bleached. Vigorous vacuuming and steam cleaning of carpets will help remove spores; of course, vacuum bags should be discarded. To reduce environmental contamination, infected cats should ideally be confined to one room until they have cultured negative. The rest of the house can be disinfected during this confinement period. Cultures of the pet are usually done monthly during the course of treatment