Skin infections caused by Staphylococcus bacteria are relatively common in dogs. The most common skin infection caused by Staphylococcus is canine superficial pyoderma, or superficial staph infection. Left untreated, this can progress to canine deep pyoderma, or deep staph infection. The prefix “pyo-” refers to pus and the word “derma” means skin.
Symptoms of a Staph Infection in Dogs
Symptoms of a superficial staph infection include patchy alopecia (hair loss) and the presence of papules or pustules and epidermal collarettes. A superficial staph infection begins as small, flat red circles on your dog’s skin called macules. As the condition progresses, the macules become raised bumps called papules. If a papule fills with pus, creating a small white dot in the middle of the raised red circle, it is called a pustule; in humans, we’d call this a pimple.
Staph infections can be pruritic (itchy) and you may notice your dog scratching or licking at these lesions. Scratching or licking at papules and pustules causes them to rupture and release clear fluid from papules and pus from pustules. When that clear fluid and pus dries, the papules and pustules become covered with a crust. If your dog continues licking and scratching at these crusty red circles, the circles get bigger and develop scales or flakes along the edge. These are called epidermal collarettes.
Symptoms of a deep staph infection include pain, swelling, crusts composed of blood and pus, and draining tracts of blood and pus from deep within the skin. Your dog will not want to have affected areas of his skin touched. He may have a decreased appetite, be lethargic, and have a fever.
Diagnosing Staph Infections in Dogs
Skin infections caused by Staphylococcus bacteria are diagnosed by skin cytology, bacterial culture and sensitivity, and ruling out other causes of similar skin lesions in dogs.
Your veterinarian will want to start with two different types of skin cytology tests: an impression smear or skin swab cytology and a skin scrape cytology. An impression smear is obtained by pressing a clean microscope slide against the affected skin. Alternatively, a piece of tape or a sterile moistened swab can be pressed against affected skin in places that are hard to reach with a microscope slide. The contents of the tape or swab are transferred to the slide, stained, and examined under a microscope.
Skin scrape cytology is used to look for Demodex and Sarcoptes mites in the skin. A sterile surgical blade is used to scrape the first few layers of skin from a small area of a lesion. The layers of skin are transferred to a slide and examined under a microscope. Demodex mites live in the hair follicles and can cause demodicosis. Sarcoptes mites burrow into the top layers of skin and cause sarcoptic mange. Both mites create skin lesions that look similar to a staph infection.
Your veterinarian may also want to examine your dog’s skin under a Wood’s lamp. Some fungal species that cause dermatophytosis (ringworm) may fluoresce an apple green color under the light of a Wood’s lamp. A fungal culture and PCR test may also be recommended to help rule out dermatophytosis as a cause for your dog’s skin lesions.
If this is not the first time that your dog is being diagnosed with a superficial staph infection, your veterinarian may recommend a bacterial culture and sensitivity. This is a test to confirm that Staphylococcus is the bacteria causing your dog’s skin infection and determine the correct antibiotic selection.
There are several ways to collect an appropriate sample for a bacterial culture and sensitivity. Your veterinarian may prick a papule or pustule so that its contents can be collected on a culture swab. If all of the papules and pustules have already been ruptured and transformed into epidermal collarettes, your veterinarian may lift the crust from over a collarette and swab the lesion underneath.
If your dog has a deep staph infection that is not responding to the antibiotic prescribed, then your veterinarian may want to obtain a small skin biopsy sample for bacterial culture and sensitivity. This can be done with a light sedative and a numbing agent applied around the affected skin. A tool called a biopsy punch is used to quickly obtain a small sample through all the layers of skin. A biopsy punch is like a cookie cutter, but it is only a few millimeters wide. Your veterinarian will close the biopsy site with a single suture.
Bacterial culture and sensitivity tests typically take 3 to 5 days to complete at a commercial laboratory. Bacteria are cultured and grown from the samples provided and then identified. Then the bacteria are tested against several antibiotics to determine which drugs should be most effective at resolving the infection.
Treating Staph Infections in Dogs
Staph infections are typically treated with a combination of oral antibiotics and medicated shampoos, mousses, sprays, or ointments. There is increasing evidence that superficial staph infections may be treated effectively with just medicated topical therapy without an oral antibiotic. Deep staph infections require an oral antibiotic.
Dogs with superficial staph infections should continue treatment until 7 to10 days after the resolution of their symptoms. For most dogs, this means that the duration of treatment is at least 3 to 4 weeks.
Dogs with a deep staph infection should continue treatment until 2 to 3 weeks beyond the resolution of their symptoms. For most dogs, this means that the duration of treatment is at least 6 weeks.
Prognosis for Dogs with Staph Infections
Staph skin infections in dogs are caused by an overgrowth of the bacteria Staphylococcus pseudintermedius. Your dog’s skin naturally has yeast and bacteria growing on its surface. This population of yeast and bacteria is called the normal skin flora. It is part of the skin’s immune system and keeps yeast and bacteria from growing on the skin surface that can cause your dog harm.
A staph skin infection caused by Staphylococcus pseudintermedius is always secondary to an underlying skin condition. Underlying skin conditions that can lead to a staph skin infection include demodicosis, sarcoptic mange, flea allergy dermatitis, dermatophytosis, canine atopic dermatitis (CAD), hypothyroidism, and hyperadrenocorticism. Your veterinarian may recommend completing a diagnostic workup, including certain skin and blood tests, to determine the underlying cause of and prognosis for your dog’s staph skin infection.
Dogs with a deep staph infection are at increased risk for developing sepsis. This is especially true for dogs that are immunocompromised or that are taking immunosuppressive drugs, such as steroids. Sepsis is a serious and life-threatening condition in which a dog’s body responds inappropriately to an infection. Thankfully, sepsis is a rare sequela to a deep staph infection.
Most dogs make a full recovery from a staph skin infection. Keys to a successful recovery include:
- Identifying the underlying skin condition that allowed the staph skin infection to occur in the first place
- Completing all treatments as prescribed by your veterinarian, even if your dog’s skin issue has resolved before treatments have been finished
The imprudent use of antibiotics has led to the development of Staphylococcus pseudintermedius strains that are resistant to one or more antibiotics. Antibiotic-resistant strains of this bacteria are known as methicillin-resistant Staphylococcus pseudintermedius (MRSP). This is not the same as methicillin-resistant Staphylococcus aureus (MRSA) in people. Effective resolution of MSRP will require aggressive treatment with oral and topical antibiotics and frequent monitoring by your veterinarian.
Are Dog Staph Infections Contagious to Humans and Other Dogs?
All dogs have the bacteria Staphylococcus pseudintermedius as part of their normal skin flora. Therefore, a staph skin infection is not contagious to other dogs in the home. Pets that reside with a dog that has been diagnosed with MSRP are not likely to develop a staph skin infection unless they also have an underlying skin condition.
Staphylococcus pseudintermedius prefers dogs and has a limited life span on human skin. Healthy people are unlikely to contract a staph skin infection from their dog. However, immunocompromised people may be at increased risk. Talk to your doctor if you are immunocompromised and your dog has been diagnosed with a staph skin infection.
