Despite its name, ringworm has nothing to do with worms. It is a fungal infection affecting the skin. Ringworm creates a scaly, crusty rash on the skin known as dermatophytosis that occurs on any part of the dog's body. It does not cause internal parasitic worms to appear in the dog or in his stool. An infected dog will display raised red, ring-like welts on his skin that scab over and cause hair loss.
There are three types of ringworm that infect domestic dogs, including Microsporum canis, Microsporum gypseum and Trichophyton mentagrophytes. All of them live in the outermost layers of skin, the dead parts that eventually slough off. They also live in hair follicles, toe nails and in the fibers of the hairs. These fungi seldom live on living tissue although one of them, Microsporum gypseum is capable of surviving in soil for a year or longer.
Ringworm is an example of a zoonotic disease, meaning that it's transmittable between animals and humans. It's extremely contagious as the spores are carried on sloughed-off skin, shed hair and toenail castings. Direct contact with infected dogs transmits the fungus to other pets or to people. Ringworm infections happen most often in hot, humid regions and usually resolve themselves within a few months without medical intervention. Dogs with lowered immunity are most prone to catching ringworm.
There are several internal parasitic worms that appear in a dog's stool. Roundworms are long unsegmented worms living in the dog's intestines. There are whipworms, so called because they move around like a whip in the intestines, and hookworms that attach themselves to the dog's intestinal walls. Threadworms are tiny worms living in the intestines and there are tapeworms, large segmented worms that reproduce themselves by breaking off segments. All can be found in the infected dog's stool.
When a dog is scratching excessively, pulling tufts of hair, biting his own skin and developing unusual rashes, he should be seen by a veterinarian. If he seems tired all the time, is weak and sleeping more than usual, he may have anemia caused by internal parasites drinking his blood. Anemia is dangerous and potentially fatal if not treated. If worms are visible in the dog's stool or vomit, this indicates parasites and should be treated immediately.
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