Itchy dog scratching
Skin diseases are common problems in dogs and cats. Many of these diseases are not contagious, but some can be transmitted to other pets or people. Two common contagious and easily transmissible skin diseases are dermatophytosis (ringworm) and sarcoptic mange (scabies). Understanding what causes these diseases and how they are transmitted and treated is key in minimizing the potential for zoonotic transmission.


Caused by a fungal organism, dermatophytosis, or ringworm, is an infection of the hair shafts and upper layer of skin. Although there are thousands of fungi in the world and approximately 30 species classified as dermatophytes, relatively few cause skin diseases. Of those that do, the infections are caused by contact with another infected animal or exposure to infective material (spores) in the environment. These spores may be found on bedding or grooming tools used on an infected animal and on any surface with which the infected animal came in contact. The spores may also be present in the environment; certain ringworm infections may be caused by fungal organisms found in soil.

Any dog or cat can develop a ringworm infection but it is most commonly diagnosed in young kittens or puppies, in animals with immunosuppressive diseases (such as cancer or other illnesses) and in animals under stress or living in high concentrations (e.g., shelters). Also, having long hair seems to be a predisposing factor in cats.

Dermatophytosis can have a highly variable appearance in animals. It can cause a single skin lesion or many lesions, or it may affect most of the pet’s skin. Some pets with dermatophytosis are itchy, while others are not. Dermatophytes infect hairs and superficial layers of the skin and nails, resulting in patches of hair loss, round or irregularly shaped skin lesions and crusty scales with irregular edges. Hairs may be broken or break easily when the pet is touched, and the skin may be red. Lesions may appear anywhere on an infected animal.

Some animals may be asymptomatic carriers, meaning that they show no signs but can still infect others and shed spores into the environment.

In people, a ringworm lesion starts as a single, red, round, mostly flat lesion with a scaly or crusty appearance. Zoonotic lesions in people typically appear on areas that come in contact with the pet, such as the abdomen, arms or face. Children are especially susceptible. Infected people may or may not itch.

Diagnosis is based on history, clinical signs and a fungal culture. Dermatophytosis is treatable and curable. Treatment for animals usually requires topical and systemic therapy. Topical therapy (rinses and soaks) helps speed resolution and minimizes the spread of spores into the environment. The disease can self-cure, but treatment is recommended to minimize its spread. Treatment can take anywhere from a few weeks to several months. Spread of dermatophytes can be minimized through routine cleaning of the home and keeping the animal isolated in a room that can be easily treated.


Sarcoptic mange, or scabies, is a fairly common disease of dogs. It’s caused by infestation of mites. (Cats can also get scabies but this condition is very rare.) Canine scabies mites are spread by contact with an infested dog or indirect contact with mites in the environment. Infested dogs often have a history of being in an animal shelter; having contact with stray dogs; or visiting a grooming, boarding or doggy daycare facility where an infested dog was present. Increasingly, we have noted a rise in cases in dogs that spend time in dog parks. Foxes, coyotes and free-roaming dogs are known to transmit the mites and may be responsible for spread of the disease.

Sarcoptic mange is an intensely itchy disease; infested dogs will usually scratch themselves until they injure the skin. The skin is often red, bald and crusty with small red dots or bumps. The less hairy skin is more likely involved; however, the entire animal may be affected. Often, lesions are first noticed on the abdomen and elbows, around the edges of the ears and under the chest. Thick crusting of the border of the ears is common. In people, a red rash is often noticed in areas that come in contact with clothes or the infested animal.

Diagnosis is based on history and clinical signs and ideally finding the mite by examining a skin scraping sample under a microscope. However, the mites are difficult to locate. Often the only way to make a definitive diagnosis is by trying a treatment and seeing if it works. Fortunately, treatment and prevention options for scabies exist. It is important to treat all animals who have been in contact with the infected animal.

How You Can Help Prevent These Diseases

  • New pets should be adopted from reputable shelters or breeders and should be screened for possible zoonotic skin diseases before you take them home. For example, every new pet should have a fungal culture performed and routine flea and tick control started as soon as the pet joins the family.
  • New pets should be isolated from other family pets to minimize the spread of potentially infectious skin diseases. Keeping the animal in one or two rooms of the home for a short time also allows the new pet time to become acclimated.
  • If you notice that your pet is scratching or losing hair, visit your veterinarian immediately. Diagnostic tests for ringworm and scabies may be warranted.
  • To minimize the chance of your pet getting ringworm, keep him away from any animals with a known infection and keep cats indoors if possible. Many infections in cats can be traced back to an indoor–outdoor lifestyle.
  • To minimize the chance of your pet getting scabies, do not allow him to come in contact with animals that are known to be infested. Check with staff at grooming, boarding and doggy daycare facilities to see if animals with scabies have been there recently. Be careful at dog parks, especially if foxes are known to inhabit the area.
  • If your pet is diagnosed with ringworm or scabies, all animals he has had contact with should be treated. Ringworm and scabies may also affect pocket pets living with an infected dog or cat. Environmental decontamination (thorough cleaning) is also essential in minimizing continued spread of the diseases.
  • People handling an infected or infested pet should practice good hygiene and thoroughly wash their hands after coming in contact with the pet. Wearing gloves is recommended when applying topical treatments.
  • If you develop skin lesions after coming in contact with infected or infested pets, consult your physician.
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