BACTERIAL SKIN INFECTIONS
- Staphylococci (‘Staph
bacteria’) are the most common organisms found in bacterial skin
diseases (pyoderma's) in dogs. Fortunately, these bacteria (S.
intermedius) are not contagious to humans or other pets.
- Commonly itchy,
yellow pustules are often observed early in the disease, and the dog’s
skin can be reddened and ulcerated. Dry, crusted areas appear as the
condition advances, along with loss of hair in the affected areas
(lesions) and an odour.
All areas of a dog’s body may be involved, but most cases are
confined to the trunk. The chin is one area commonly affected. Called
chin acne, this condition is actually a deep bacterial infection.
Obese dogs and dogs of the pug-nosed breeds are frequently affected by
pyoderma in the skin folds on their face, lips and vulva.
Other areas where pyoderma may occur include between the toes and on
the calluses of the elbows that mostly affects the abdominal area in
- This is usually made from the case history
and appearance and location of the lesions. In some cases, it may be
necessary to culture the skin (grow the bacteria) and conduct
sensitivity tests to determine which antibiotic will be effective in
treatment. Most bacterial skin infections in dogs are secondary to
another disease such as parasitism, allergies, endocrine (hormonal)
disorders or abnormalities in the immune system. Therefore, in
recurrent cases, it is important to search for underlying causes. It
may be necessary to do blood tests, allergy tests or skin biopsies to
achieve a complete diagnosis.
- Initial treatments may entail removal of the
hair in and around the lesions, washing of the whole dog with
antibiotic shampoos such as benzoyl peroxide, careful drying and the
application of an antibiotic ointment to local lesions, in most cases,
antibiotics will also be administered orally for 3-4 weeks. Bandages
or a protective collar which prevents the dog from mutilating the
lesions may be applied.
Some pyoderma involving skin folds can require corrective surgery. In
recurrent cases where testing reveals no definable underlying cause,
special staphylococcal vaccines as an alternative to long-term
antibiotic treatment can be tried.
It may be necessary to continue treatments such as antiseptic
shampooing, antibiotic ointment applications and giving antibiotics
orally at home. While most cases respond to treatment, recurrences of
pyoderma are common, particularly if treatment recommendations and
follow-up visits to your veterinarian are neglected. Glucocorticoid
steroids cannot be administered.
Fungal Skin Infections (Ringworm)
- The fungal skin infections of dogs are caused
primarily be two species of fungi: Microsporum and Trichophyton. The skin
diseases resulting from these fungi are commonly called ‘ringworm.’
- Ringworm is seen most commonly in young dogs.
The fungi live in dead skin tissues, hairs and nails. Hair loss, usually
in circular patches, may appear. If infected, the center of the patches
may have a dry, crusty appearance. The head and legs are most commonly
affected by ringworm, although the disease may spread over other parts of
the dog’s body if not treated. Dogs may scratch the lesions.
- The appearance of the lesions, the history
of their development and the age of the dog are all helpful in diagnosing
ringworm. A Wood’s Lamp Test (ultraviolet light) can be used to help
diagnose the Microsporum species only. A definite diagnosis can be
obtained through a fungal culture -- grow the fungi found on the affected
- The hair around
the lesions is clipped, and special fungicidal shampoos or rinses are used
for bathing the dog. Topical lime sulfur and mandatory systemics should be
Public Health Aspects of Ringworm - Ringworm is contagious
to humans, particularly to children and to other household pets. Infected
dogs should be kept away from children and other dogs and cats until the
infection is cures -- which can be as long as 2-3 months or more after the
treatment begins. Adults should be careful to wash their hands thoroughly
after handling an infected dog. If treated early, ringworm is readily
controlled in humans. Other household pets should also be examined for
Allergic Skin Diseases
Allergies in dogs are common. Signs such as itchy skin, nasal and eye
discharges and sneezing, and/or digestive upsets and/or skin lesions may
indicate an allergy is present. Many skin diseases seen in dogs are caused
by an allergy.
- An allergy is a hypersensitivity reaction to
allergy-causing substances known as ‘allergens’ or ‘antigens.’
Dogs (like people) can develop allergies at any age, and the signs can
appear quite suddenly.
The most common allergy dogs develop is the flea
saliva. The presence of a single flea on these allergic dogs causes
intense itching. These allergies are seasonal in climate zones where fleas
are eliminated by the cold in winter months -- and a year-round problem in
Atopy (atopic dermatitis, allergic inhalant dermatitis) is a pruritic
(itchy) skin disease dogs develop in response to inhaled particles such as
house dust, molds and pollens. This common form of allergy usually starts
at a relatively young age. Rarely, dogs can be allergic to chemicals
contained in soaps, waxes, carpets and flea collars. This type of
hypersensitivity is known as a ‘contact allergy.’ Also, some dogs are
allergic to insect bites and stings. Food allergies usually case diarrhea
and/or skin lesions.
- Itching is the primary sign of allergic skin
diseases in dogs. The affected skin may appear normal, or red and moist in
patches called ‘hot spots.’ Pus and dried crusts are apparent if a
bacterial infection is also present. The dog tends to constantly scratch
and lick affected areas. Initially, flea allergies are most evident over
the dog’s back and near the tail. A dog’s face, feet, chest, and
abdomen are more often affected by pollen and dust-type allergies. Contact
allergies are seen mostly on the hairless areas of the abdomen and on the
bottoms of the feet.
- The dog’s case history helps with the
diagnosis. The intense itching and location of the lesions are also
helpful in diagnosing the type of allergy present. Response to treatment
(flea control) is often used as a method of diagnosis of flea allergy.
Trials of special hypoallergenic diets are used to diagnose food allergy.
Allergy testing is used to help choose immunotherapy. Blood tests are also
available to diagnose allergies, but their use is more controversial. Ask
your veterinarian for his or her current recommendations.
- Allergies can be controlled in most cases,
with few ‘cured.’ Antihistamines and corticosteroids may be used by
your veterinarian to give your dog relief from the intense itching. In
most cases this will stop the self-mutilation. The owner will be
instructed to give corticosteroid tablets in decreasing dosages for a few
months. Corticosteroids are potent drugs and should not be used carelessly
or for long periods of time. The main objective in controlling flea
allergies in dogs is to kill the fleas on the dog and in the dog’s
Another approach to allergy control is hyposensitization (immunotherapy).
In this procedure, a correct diagnosis by intradermal or blood testing is
necessary. The dog is then given injections of small but increasing doses
of the allergy-causing substance at varying intervals for up to 12 months.
Lifelong response may take up to 12 months.
Parasitic Skin Diseases
- Fleas are the most common parasitic skin disease
found in dogs. Mange is another type of skin disease which is caused by
mites. There are two severe types of mange: sarcoptic mange and demodectic
- Ear mites, lice, and ticks are other parasites that affect dogs. Their
presence irritates the dog, leading to self-mutilation.
- Sarcoptic mange causes intense itching,
loss of hair and crusting of the skin. A dog’s ears, front legs, chest
and abdomen are most often affected by sarcoptic mange.
- Demodectic mange can cause itching. The skin is reddened
and scaly, and hair loss occurs in round patches resembling ‘ringworm.’
The face and front legs are most commonly affected, although some cases
may be generalized. Generalized demodectic mange is often a sign of
underlying internal disease or a hereditary problem.
- Ear mites cause severe irritation in the ears. Often, an
affected dog will scratch the hair off the back of its ears. Ticks, lice
and fleas may transmit other diseases, in addition to causing
- Mange is often suspected on the basis of the
case history and the appearance and location of the lesions. A skin
scraping test is always performed to aid in identifying parasites. Ear
mites, which are barely visible to the naked eye, appear as small white
objects. The black debris commonly seen in the ears of dogs with ear mites
is a combination of dried blood, normal ear wax and discharges from
inflammation. Lice, fleas and ticks can also be seen by close examination
of the dog’s skin.
- Mange is treated by clipping the affected
areas and washing them with an antiseptic. Antimite dips are often
necessary and may be used weekly or biweekly for several months. Shampoos
can be sued before each dip. The dog’s eyes should be protected with
mineral oil or eye ointment and the ears plugged with cotton before
dipping. Most cases of mange respond well to this treatment. Antibiotics
can be administered in cases of mange where infection may be present.
Ear mites can be readily treated Initially, your veterinarian may
recommend a thorough cleaning of the dog’s ears while the animal is
sedated. This treatment can be followed up with home treatments using
special solutions or ointments to kill the mites and prevent infections in
addition, insecticidal dips, sprays, powders or shampoos are often
Lice, ticks and fleas must be killed on the dog and in the dog’s
environment with insecticides. Dips, shampoos, flea collars, sprays,
powders, foams and foggers containing insecticides are available from your
veterinarian to help control these parasites.
Hormonal Skin Diseases
Skin diseases caused by hormonal abnormalities in dogs are difficult to
diagnose. The thyroid gland, adrenal glands, pituitary gland, testicles
and ovaries all produce hormones. If excessive (‘hyper’) or deficient
(‘hypo’), these hormones produce changes in the skin and hair coat.
Most hormonal problems that affect the skin produce hair loss that is
evenly distributed on each side of the dog’s body. The skin may be
thicker or thinner than normal, and there may be changes in the color of
the skin or hair coat. These diseases usually are not itchy.
When any of the hormone-producing glands malfunction, they affect other
body functions besides the skin. Hormonal skin diseases in dogs can be
much more serious than a ‘skin problem.’
Some causes of hormonal skin disease, such as hypothyroidism and adrenal
gland problems, can be diagnosed by special blood tests and effectively
treated. Others may be more difficult to diagnose and treat. Skin changes
related to the sex hormones can be successfully treated with surgical
neutering, if this has not been performed previously.
From Columbia Animal Hospital