What Causes Staph Infections in Dogs?
Staph infections in dogs are caused by bacteria. No surprises there. But did you know that bacteria is actually a normal part of your pet's microbiome? The microbiome is a natural combination of bacteria, fungi, viruses, and parasites that live on or in the bodies of dogs, humans, and other animals. Believe it or not, these microbes are beneficial when they are kept in balance.
All dogs have several species of Staphylococcus bacteria from birth and they likely acquire it from their moms and their environment, says Amelia White, DVM, MS, DACVD, Associate Clinical Professor of Dermatology at Auburn University College of Veterinary Medicine in Auburn, Al. "In healthy dogs," she explains, "this bacteria can typically be found in the mucous membranes (e.g. nose, mouth, genitals). It only becomes a problem for dogs when they become sick or injured."
What Causes Staph Infections in Dogs?
"Staph" (pronounced staff) infections in dogs are caused by an overgrowth of Staphylococcus bacteria. Staphylococcal bacteria on your dog's skin is normal, but staph infections of the skin (also called staphylococcal dermatitis) definitely aren't. The difference between the two comes down to the pet's skin barrier and immune system. When these are compromised, infection can occur.
"When animals become ill, pathogenic (i.e. disease-causing) bacteria inhabiting the skin can overgrow the 'good' bacteria and lead to infections at various body sites," White explains. "For example, dogs with allergic skin disease have dysbiosis of the microbiome, or an imbalance of good and pathogenic bacteria. During an allergy flare, these pathogenic bacteria are found in higher numbers on the skin and are thought to contribute to the inflammation and unhealthy condition of the skin."
This irritation of the skin's barrier, coupled with the scratching, chewing, and licking that tends to accompany allergies in dogs, can allow opportunistic staphylococcal bacteria to penetrate and infect the skin.
In addition to allergies (like flea allergies, food allergies, atopic dermatitis, or seasonal allergies), the Merck Veterinary Manual notes that staph infections can be triggered by:
- Skin wounds or burns
- Hormone issues (such as hypothyroidism)
- External parasites (such as mange or fleas)
- Hair follicle abnormalities (like follicular dysplasia)
- Keratinization disorders (such as seborrhea)
- Poor grooming
- Anatomy (such as deep skin folds)
Staph infections can occur in any dog regardless of breed or age, but they are more common in older pets because their immune systems are weaker.
Signs and Symptoms of Staph Infections in Dogs
The signs of staph infections in dogs largely depend on where the infection is located, White says. Bacterial infections of the skin (commonly referred to as pyodermas) can affect both the superficial and deeper layers of the skin, she continues. According to the Merck Veterinary Manual, superficial infections typically affect a dog's chest and abdomen. Deeper infections are more commonly found on the muzzle, chin, between the toes, and on pressure points like elbows, knees, and hocks (lower part of hind legs).
Superficial skin infections are the most common skin infections in dogs, says White. Common signs include:
- Red, hot, swollen skin
- Skin lesions like papules (small, red bumps), pustules (acne), crusts, and erosions
- Hair loss
Dogs with deeper infections in the dermal and fat layers of the skin may show these signs:
- Nodules or masses that are painful to the touch and produce blood and pus when ruptured
- Decreased appetite
If you see any of the above signs in your pet, regardless of whether they correspond to superficial or deep infections, it's time to take your dog to the veterinarian.
Diagnosis and Treatment for Staph Infection in Dogs
If you suspect your dog has a staph infection, your veterinarian will need to physically examine your pet and will likely recommend various tests (like a bacterial culture or skin cytology) to get to a diagnosis. Because staph infections are secondary infections, it's crucial to determine the primary cause so it can be treated as well. If the primary cause is not addressed, it is very likely that the staph infection will continue to come back!
According to White, topical antiseptic therapies are safe and effective treatments for staph infections. "This includes the use of medicated shampoos, sprays, wipes, mousses, and creams for several weeks," she explains. "When bacterial infections are in the bloodstream or deeper layers of skin, antibiotics are administered as pills or injections to help treat the infections."
White notes that the treatment regimen required for staph infections can be tricky for pet parents to follow—especially those with busy schedules and dogs who are difficult to medicate—but that it's vital to remain diligent for the sake of antibiotic resistance. "When these medications aren't administered on time or for a long enough duration, antibiotic resistance is more likely to develop," she continues. "Resistant skin infections like methicillin-resistant (MRS), multidrug-resistant (MDRS) Staphylococcus are common in both human and veterinary medicine, and they complicate treatment." It's very important to use all of the medications prescribed by your veterinarian.
Moreover, because staph infections are contagious, White says that an antibiotic-resistant infection in one pet poses a risk to other pets and even people living in the same home (especially if they have suppressed immune systems or open sores). If your pet is diagnosed with an antibiotic-resistant staph infection, your veterinarian will likely suggest extra precautions, such as wearing gloves when handling infected items and regularly disinfecting surfaces with bleach.
Once the staph infection is treated, White says it's important for pet parents to follow up with their veterinarian to make sure the primary cause of infection has been properly diagnosed and managed. "When the primary disease is left untreated," she explains, "the skin infection will return." So, it's best not to assume that your dog's staph infection is gone just because the skin looks better.