Dog - Staphylococcal Dermatitis & Hypersensitivity

What is staphylococcal dermatitis?

Dermatitis is the name given to inflammation of the skin.  Staphylococcae are a type of bacteria which are commonly found both on humans and animals.  In normal circumstances they are considered to be commensal, i.e. on healthy skin they cause no harm.  If the skin becomes damaged they can multiply rapidly and cause a surface pyoderma infection, i.e. staphylococcal dermatitis.

What is likely to cause the skin damage?

Scratching is the most common cause.  Any problem that causes pruritus (itching) can trigger staphylococal dermatitis.  Common causes are fleas and certain allergies as well as irritating chemicals, e.g. just walking in a fuel spillage, paraffin, etc.

How is the condition diagnosed?

Acute staphylococcal dermatitis is usually initially diagnosed on physical appearance.  There are basically two types.  One type starts as a red area on the skin with a pimple-like pustule in the centre.  The other type is a circular, reddish area with a crusty edge and hair loss.  This can easily be confused with ringworm but either of these skin problems in a dog that is scratching is highly suggestive of the condition.

Confirmation should be made with bacteriological cultures and/or skin biopsy.  It should be borne in mind that MRSA can affect our dogs.  It is important with any staphylococcal  infection to determine the antibiotic sensitivity of the bacterium as soon as possible.

How is the condition treated?

Staphylococcal skin infections are usually sensitive to several antibiotics.  Because of the possibility of developing staphylococcal hypersensitivity (see below) we may suggest that treatment continues for three to six weeks even though the lesions appear to have cleared. Antibacterial shampoos and ointments are also used to help establish rapid control of the infection.

Since the pruritus (itching and scratching) may have been present before the staphylococcal infection occurred, other tests may be needed to determine the reason for the pruritus.

Am I or any of my other pets likely to catch the condition?

In normal circumstances staphylococci live on the skins of normal dogs, cats and people without causing problems. It is only when the skin is injured or diseased that problems arise. The staphylococci then become pathogenic (disease producing).  In view of the risk of MRSA,   which can pass between pets and people, it is important that antibiotic sensitivity tests are undertaken to establish the most suitable treatment for the condition and whether or not it is one of the strains of antibiotic resistant staphylococcae.

My dog was treated for staphylococcal dermatitis for almost two months.  Two weeks after completion of treatment, lesions have returned.   What is happening?

This may be due to an allergy that the dog has developed to the staphylococcal bacteria.  This is called staphylococcus hypersensitivity or staphylococcus allergy.

The hypersensitivity lesions appear identical to those caused by staphylococcal dermatitis.  With correct treatment the staphylococcus causing the original dermatitis should be eliminated.  As stated previously these bacteria are normal inhabitants of the skin. Following treatment for the allergy/infection the skin lesions clear up but, if your dog is allergic (has a hypersensitivity), skin lesions will return within a few days or weeks since the original organism is likely to return to colonise the skin and an allergic reaction will occur.  Treatment for the hypersensitivity (allergy) may have to be repeated long term.

How is staphylococcal hypersensitivity treated?

Initially the treatment is the same - appropriate antibiotics, medicated baths and drugs to control the pruritus.  If following special allergy testing it is found that the problem is due to staphylococcal hypersensitivity, it may be necessary to administer a special vaccine (staphylococcal bacterin).  This is intended to reduce the dog's sensitivity to the organism and involves a series of injections.  Should this prove necessary we will discuss the subject fully with you.

Is such treatment likely to be successful?

In dogs with a pruritus (itchy) allergy, we expect up to 75% response although booster shots frequently have to be given on a regular basis.

What happens if this allergy treatment is not successful?

Your dog will have to be treated periodically with appropriate oral antibiotics and medicated baths.  Repeat antibiotic sensitivity tests in respect of the staphylococcal organism may have to be performed in order to ensure that the most suitable treatment is maintained over time since as previously mentioned, staphylococcal organisms frequently develop antibiotic resistance.