Ringworm Susceptibility

Identification

• Most cases of ringworm are caused by one of three fungi: Microsporum gypseum, Microsporum canis or Trichophyton mentagrophytes. Although these spores are typically found in hot, humid areas, most ringworm cases ironically occur in autumn and winter. Animals that are infected with ringworm may shed spores that can survive for a year and a half. This means a kennel that once housed an infected dog may still pose a ringworm threat more than a year later. While milder cases of ringworm may clear up on their own, more advanced cases require medical treatment. Ringworm typically occurs in young dogs, whose immune system is not yet fully developed, and in dogs whose immune system is compromised due to other diseases or medications.

Immune System Function

• The immune system functions by recognizing foreign "invaders" to the body such as bacteria, viruses and fungi. Contact with these foreign substances trigger an immune response, during which specialized cells gather to destroy them. The largest area of the immune system is the skin, since it is the first area of contact for most foreign substances. In a healthy dog, the skin can successfully repel a threat, such as that from bacteria or fungus, before it progresses into something more serious.

Weakened Immune System Factors

• Several factors contribute to a weakened immune system in dogs. Young dogs whose immune systems are still developing are less able to fight off bacterial, viral or fungal threats than adult dogs. Vaccinations given during these early weeks and months additionally tax the immune system. Conversely, older dogs--especially those with other underlying medical conditions--have depleted immune systems that make them more susceptible to disease. Additional immune system stressors include cortisone shots, used to treat conditions such as arthritis and hip dysplasia, and poor diets.

Symptoms

• Ringworm causes small lesions of scaly skin, which are easily noticeable since the fur will typically fall off in those areas. These lesions are most often located on the head, although they can occur on other areas of the body as well. The infected areas may continue to grow in size, and the dog may itch at the lesions, but there may also be no obvious sign of irritation. In some instances, the ringworm will spread across an area, particularly the face, rather than forming smaller lesions. Such cases can be mistaken for mange, which is another skin infection that is typically contracted by dogs with weakened immune systems.

Diagnosis

• There are three main methods of diagnosing ringworm in dogs. A special black light may be used, which causes areas infected by ringworm to glow a florescent green. However, this method is not always accurate since some strains of ringworm will not show up. Hairs near an infected area may be extracted and examined under a microscope using a potassium hydroxide solution, which dissolves the skin cells but leaves fungus cells intact. The most accurate diagnosis is obtained by a skin culture, in which the infected skin is scraped and examined for evidence of ringworm.

Prevention

• The best way to prevent a dog from contracting ringworm is to avoid environments where ringworm spores may be present. Kennels, dog shows, grooming facilities and even veterinary hospitals pose a risk of ringworm infection for dogs whose immune systems are unable to keep the fungus at bay. It is also possible for ringworm to be transmitted from dogs to people. This is especially true for individuals whose immune systems are suppressed, either through disease or medications. Always protect yourself by wearing gloves when touching infected animals, and thoroughly wash hands afterwards. Since an infected dog can spread spores in its living space, bleach should be used to clean these areas, as well as any exposed bedding.