Rats may suffer from ringworm occasionally. This problem is not caused by a worm as its name suggests, but is in fact a fungal disease. The fungi (or dermatophytes) colonize keratinized tissue (skin, hair and claws) causing a disease properly known as dermatophytosis. Ringworm gets its name from its appearance in humans in which it forms a red ring of scaly skin.
Ringworm is spread by direct contact between mammals, including humans and it is also carried on bedding and other fomites such as cages, toys and clothing. It is spread relatively easily between animals but not all animals carrying the fungal infection will show clinical signs of it. Rats may be more susceptible to developing ringworm lesions if their immune system is compromised in some way, for example by stress caused by poor husbandry or corticosteroid therapy causing immunosuppression.
If your rat has ringworm you may notice lesions on the skin. These may be red areas of skin which may or may not be itchy or more commonly will be scaly patches of skin; there may or may not be hair loss associated with these lesions. Often the lesions appear to be roughly circular in shape (like a ring). Ringworm lesions may occur on any part of the body but is often seen at the base of the tail or along the back and neck. The disease is caused by a fungal infection (Trichophyton and Microsporum spp) not a worm as the name of the disease would suggest.
Your vet may be able to diagnose ringworm on your rat using a special light called a Wood's lamp; this lamp emits ultraviolet light. When ultraviolet light is used some types of ringworm may show up as apple green florescent areas on the skin. Not all types of ringworm will shine in this way however and your vet may need to take some skin or hair samples to culture or examine under a microscope in order to reach a diagnosis.
If your rat does have ringworm oral medication may be required. A drug called griseofulvin is often used as is ketoconazole. Medication is often required for 4 to 6 weeks and sometimes longer. Shampoos, ointments and lotions may also be used in conjunction with this treatment but they do not seem to be as effective if they are used alone. Sometimes there may be secondary infection of the skin with bacteria and if this is the case then this will need to be treated too.
Ringworm is easily spread between mammals so all animals in contact with an infected rat are at risk of contracting the disease. Prevent the spread of ringworm by employing good methods of hygiene. If your pet has this disease then you will need to thoroughly disinfect the cage and change the bedding. Since bedding materials may be contaminated with ringworm it may be useful to freeze it then thaw it before use. Cages of infected animals should be disinfected thoroughly possibly using a weak solution of bleach, but do rinse and air it well afterwards.
All mammals can suffer from ringworm and humans can catch this disease too. If you suspect your rat has ringworm take it to your vet. If you need to handle or treat the infected rat you should wash your hands thoroughly afterwards. In humans this disease tends to cause red and itchy patches of skin but it is generally easily treated, often with over-the-counter medications.