Canine Ringworm
All You Ever Wanted To Know About Canine Ringworm
Although dogs are susceptible to many parasitic infections, canine ringworm is actually a fungal infection that has nothing to do with worms. It is called ringworm because of the appearance of the lesions caused by the fungi. The term ringworm is less descriptive for canines than it is for humans, who are also susceptible to the fungi. In humans, the fungal infection causes a circular lesion with healing skin in the center, and a ring of scaly skin on the outside. The term ringworm refers to this outside ring of irritated skin that resembles a worm. In canine ringworm, the infection is not always ring-shaped. It can look like any type of skin lesion, but is most often a dry and scaly patch of skin that is gray in color.
Canine ringworm is caused by fungi known as dermatophytes, which feed on dead skin and hair cells. The fungi live in the hair follicles, where they cause damage to the hair shaft that results in hair loss and skin irritation. Ringworm is spread by contact with infected animals or items, and is highly contagious among animals. Ringworm can also be spread between animals and humans, although certain people are at an increased risk. People are more likely to contract ringworm if they have a suppressed or reduced immune system; this includes people such as children, elderly people, those with HIV, people on certain medications, and people who are under a great deal of stress.
Canine ringworm most commonly occurs on the face, tips of the ears, tail, and paws. Skin lesions will form within 12 days of exposure to the fungus. The lesions will have a scaly appearance and, in some cases, may be itchy. As with humans, the skin at the center of the lesion will begin to heal first. Although canine ringworm is not as characterized by the ring-like shape as human ringworm, in some cases it may cause your pet's hair to break in a ring-shaped pattern.
Your vet can perform several tests to determine if your dog has ringworm. One simple option is to use a Wood's light, an ultraviolet light that causes the most common ringworm fungus to fluoresce about half the time. This is not a definitive diagnosis, but may be enough to confirm what your vet suspects from a physical examination. Another option is to examine hairs from your pet under a microscope, to look for fungi spores. Spores are very difficult to see, but if they are seen to be present you can be sure your pet has ringworm. A third option is a fungal culture, in which hairs and skin scales are taken and used to attempt to grow the ringworm fungi. This test takes at least 10 days, because fungi grows quite slowly. It is useful, however, because it can both confirm a diagnosis of ringworm and tell precisely which of several possible species of fungi is responsible for the infection. This is the only test that can be used on animals that are not showing signs of ringworm, as the other tests require a specific lesion in order to work. Therefore, the fungal culture test can be used to determine if any of your animals is a carrier of the fungus with no symptoms. Finally, a biopsy can always be done to look for fungal spores and obtain a definitive diagnosis.
There are several possible courses of treatment for canine ringworm. Oral medications are available, although they have some downsides. They must be continued for 1-2 months, they can be rather expensive, and they must be given to your pet with food. They also should not be given to a pregnant animal, as they can cause birth defects. Topical treatments are another option. They are advantageous because they work by actually killing the fungi on contact, while the oral medications stop fungi reproduction and allow the live fungi to continue to contaminate the pet's environment. If left untreated, canine ringworm will probably go away on its own after about four months. Because the fungus is so contagious, a period of four months allows for much opportunity to spread the fungus and reinfection, and it is best to treat the ringworm to speed up the recovery process.