Zoonosis: An infectious disease in animals that can be transmitted to people. The natural reservoir for the infectious agent is a animal.
One of the first misconceptions that I have to clear up with some of my clients is that ringworm isn't actually a worm. It's a type of fungal infection of the skin and is related to other fungal diseases such as jock itch and athlete's foot. The name comes from the ring-like progression of the lesion once it becomes established in the superficial layers of the skin. Many kinds of animals can get ringworm, including dogs, cats, rabbits, and guinea pigs.
The fungi that cause ringworm can be found contaminating the environment, and this is usually how humans and animals become infected. Once infected, that animal then becomes contagious, and can transmit the disease by contact. On animals the lesions look like scaly, hairless areas, most commonly on the head (though they can appear anywhere). Most of the time these areas do not cause itchiness, but if it progresses far enough they can be irritating.
Luckily, this is not a serious disease. In pets we most commonly make a definitive diagnosis by collecting hair from an affected or suspicious area and growing a culture to identify the organism. There are other, quicker methods of diagnosis, such as using a blacklight, but they are not as accurate as the culture. Once diagnosed, there are several methods of treatment, depending on how wide-spread the infection is and how long it has been going on. Most of the time treatment will consist of topical lotions or antifungal shampoos, though severe cases may require oral medications. Long-haired pets may also need to be shaved to reduce the numbers of spores on the skin.
If your pet has any sores that sound like this, make sure you visit your vet for a proper diagnosis. Doing so can not only help the pet, but can help the humans in the family with quick prevention or treatment.