Effects of Dog Disorders on Human Skin

Dog skin disorders are among the most common health problems in dogs. Skin disorders in dogs have many causes, and many of the common skin disorders that afflict people have a counterpart in dogs. The condition of dog's skin and coat can also be an important indicator of its general health. Skin disorders of dogs vary from acute, self-limiting

problems to chronic or long-lasting problems requiring life-time treatment. They also need to be differentiated on the basis of being of primary or secondary (due to scratching, itch) in nature, making diagnosis complicated.^[1] Dog skin disorders may be grouped into categories according to the causes.

Types of disorder

Immune-mediated skin disorders

Skin disease may result from deficiency or overactivity of immune responses. In cases where there is insufficient immune responses the disease is usually described by the secondary disease that results. Examples include increased susceptibility to demodectic mange and recurrent skin infections, such as Malassezia infection or bacterial infections. Increased, but harmful immune responses, can be divided into hypersensitivity disorders such as atopic dermatitis, and autoimmune disorders (autoimmunity), such as pemphigus and discoid lupus erythematosus.
 

Canine Atopic Dermatitis

Canine atopy is a hereditary^[2] and chronic allergic skin disease. It usually starts between 6 months and 3 years of age with some breeds of dog such as the Golden Retriever starting at an earlier age. Dogs with AD are itchy, especially around the eyes, muzzle, ears and feet. In severe cases the irritation is generalised. In cases where the allergens are seasonal the clinical signs of irritation are similarly seasonal, but many dogs with house dust mite allergy have perennial disease.^[3]

Canine Atopy with dermatitis around the eye created by rubbing

Some of the allergens associated with canine AD include pollens of trees, grasses and weeds, as well as molds and House dust mite. Ear and skin infections with the bacteria Staphylococcus pseudintermedius and the yeast Malassezia pachydermatis are common secondary to canine AD. Flea allergy is commonly associated with AD. AD is a lifelong condition in most dogs.
Food allergy can be associated with identical signs and some authorities consider food allergy to be a type of atopic dermatitis.
 
Diagnosis of AD is by elimination of other causes of irritation including fleas, scabies and other parasites such as Cheyletiella and lice. Food allergy can be identified through the use of elimination diet trials in which a novel or hydrolysed protein diet is used for a minimum of 6 weeks and allergies to aeroallergens can be identified using intradermal allergy testing and/or blood testing (allergen-specific IgE ELISA).

Treatment for AD includes avoidance of the offending allergens if possible, but for most dogs this is not practical or effective. Other treatments modulate the adverse immune response to allergens and include antihistamines, steroids, ciclosporin and immunotherapy (a process in which allergens are injected to try to induce tolerance).^[5] In many cases shampoos, medicated wipes and ear cleaners are needed to try to prevent the return of infections.
 
New research into T-cell receptor peptides and their effects on dogs with severe, advanced atopic dermatitis are being investigated by Animal Health Consulting, LLC.

Autoimmune skin diseases

Pemphigus foliaceus is the most common autoimmune disease of the dog. Blisters in the epidermis rapidly break to form crusts and erosions most often affecting the face and ears initially, but in some cases spreading to include the whole body. The pawpads can be affected causing marked hyperkeratosis (thickening of the pads with scale). Other autoimmune diseases include bullous pemphigoid and epidermolysis bullosa acquisita.
 
Treatment of autoimmune skin conditions requires treatment to markedly reduce the abnormal immune response; steroids, azathoprine and other drugs are used as immunosuppressive agents.

Physical and environmental skin diseases

Hot Spots

A Hot Spot, or acute moist dermatitis, is an acutely inflamed and infected area of skin irritation created and made worse by a dog licking and biting at itself. A hot spot can manifest and spread rapidly in a matter of hours as secondary Staphylococcus infection causes the top layers of the skin to break down and as pus becomes trapped in the hair. Hot spots can be treated with corticosteroid medications and oral as well as topical antibiotic application, as well as clipping hair from around the lesion. Underlying inciting causes include flea allergy dermatitis, ear disease or other allergic skin diseases. Dogs with thick undercoat are most subject to getting hot spots.

Acral lick granulomas

Lick granuloma from excessive licking

Related to Hot Spots are Lick granulomas, a raised, usually ulcerated area on a dog's wrist or ankle area caused by the dog's own incessant compulsive licking. According to the Merck Manual of Veterinary Medicine, compulsive licking has the following necessary condition: licking in excess of that required for standard grooming or exploration. The following condition is sufficient: licking in excess of that required for grooming or exploration that represents a change in the animal’s typical behavior and interferes with other activities or functions (e.g., eating, drinking, playing, interacting with people) and cannot easily be interrupted.^[6]

Infectious skin diseases

A dog with skin irritation and hair loss on its leg caused by demodectic mange

Infectious skin diseases of dogs include contagious and non-contagious infections or infestations. Contagious infections include parasitic, bacterial, fungal and viral skin diseases.
One of the most common contagious parasitic skin diseases is Sarcoptic canine scabies. Another is mange caused by Demodex (Demodicosis), though this form of mange is not contagious. Another contagious infestation is caused by a mite, Cheyletiella. Dogs can be infested with contagious lice.
Other ectoparasites, including flea and tick infestations are not considered directly contagious but are acquired from an environment where other infested hosts have established the parasite's life cycle.
Ringworm is a fungal skin infection and is more common in puppies than in adult dogs.

Dog with dermatitis caused by Malassezia (yeast)

Non-contagious skin infections can result when normal bacterial or fungal skin flora is allowed to proliferate and cause skin disease. Common examples in dogs include Staphylococcus intermedius pyoderma, and Malassezia dermatitis caused by overgrowth of Malassezia pachydermatis.
 

Hereditary and developmental skin diseases

Some diseases are inherent abnormalities of skin structure or function. These include seborrheic dermatitis, ichthyosis, skin fragility syndrome (Ehlers-Danlos), hereditary canine follicular dysplasia and hypotrichosis, such as color dilution alopecia.
Puppy strangles is a developmental skin disease of puppies of unknown etiology.
 

Cutaneous manifestations of internal diseases

Some systemic diseases can become symptomatic as a skin disorder. These include many endocrine (hormonal) abnormalities, such as hypothyroidism, Cushing's Syndrome (hyperadrenalcorticism), and tumors of the ovaries or testicles.