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Bacterial and Fungal Infections in Dogs

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Diagnosing and Treating Canine Bacterial and Fungal Infections

Dogs are susceptible to a wide range of bacterial and fungal infections, especially when they spend a lot of time outdoors. These infections can be worrisome for pet owners because some bacterial infections can be fatal if treatment is not administered promptly.

In this guide, we'll provide an overview of the most-common bacterial and fungal infections found in dogs and how they can be treated.

Most Common Bacterial Infections in Dogs

Leptospirosis—Leptospirosis is a bacterial infection caused by a bacterium known as spirochetes that can affect both humans and animals. Dogs typically contract this infection from contaminated, stagnant water, or from coming in contact with urine from other animals infected with the bacteria. Dogs also may get it through bites or from mating with other infected dogs.

Symptoms of leptospirosis may include fever, lethargy, depression, vomiting, and redness of the mucous membranes. In the case of serious infection, a dog can develop kidney inflammation, which can result in permanent damage to the kidney. Treatment for leptospirosis requires an antibiotic like doxycycline.

Staphylococcal Infection (staph infection)—Staph infection is caused by the bacterium Staphylococcus sp. and is the most-common type of bacterial skin infection seen in dogs. It also can affect a dog's upper respiratory tract or its skin. Staph infections can be treated using antibiotic shampoos and ointments for skin infections, and oral antibiotics like erythromycin, clindamycin, or cephalexin. Staphylococcus is potentially a zoonotic risk, meaning it can be transmitted from a dog to a human and vice versa, so early treatment and good hygiene practices are important.

Bacterial Ear Infection—A dog can develop a bacterial ear infection when there is underlying inflammation. This is common with allergies, excessive moisture within the ear canal, and co-infection with yeast species called Malassezia. While a healthy dog usually can defend himself against this bacterium, a dog who has a weakened immune system may find it more difficult.

Signs of a bacterial ear-infection include itchy, red, and inflamed inner ears, bad odor and waxy build-up in the ear. If the eardrum is intact, bacterial ear infections can be treated using gentamycin, tobramycin, or amikacin.

Actinomycosis and Nocardiosis—Actinomycosis is an infection that's caused by Actinomyces sp. and Nocardia sp. Bacteria. Both bacteria are found predominantly in soil. The infection occurs when the bacteria enters the skin through a wound or abscess. If the infection isn't treated using a beta-lactam penicillin-type antibiotic like carbenicillin, it may make its way deeper into the chest or abdomen, where it causes pus to accumulate.

Most-Common Fungal Infections in Dogs

Aspergillosis—Aspergillosis is a fungal infection caused by a species of mold called Aspergillus. These fungi most commonly affect dogs with weakened immune systems. The nasal form of the disease is the most common, with transference occurring through your dog's nose and sinuses. The disease also can develop in other organs in the body.

Common symptoms may include sneezing, bleeding from the nose, nasal discharge, swollen nose, and decreased appetite. Veterinarians can treat Aspergillosis with an antifungal medication like ketoconazole, fluconazole, or itraconazole.

Cryptococcus—Cryptococcus is caused by a yeast-like fungus called cryptococcus neoformans. Dogs contract this disease by inhaling the spores found in soil that has been contaminated by bird droppings.

Cryptococcus can affect a dog's brain, eyes, lymph nodes, and skin. Symptoms include coughing, imbalanced gait, circling, seizures, inflammation of the eyes, blindness, and swollen lymph nodes. Cryptococcus is treated using imidazole-based medicines like miconazole or clotrimazole.

Blastomycosis—Blastomycosis is a regional systemic fungal disease that can be found along the Eastern seaboard, in the Great Lakes region, and in the Mississippi River valleys. The fungus is prevalent due to the moist, rotting, organic debris and bird droppings commonly found in the area. A dog can get this disease by inhaling infected spores.

The symptoms are seen in the respiratory system, with coughing, weight loss, and lameness being the most common. If left untreated, blastomycosis may result in pneumonia. Blastomycosis is treated using ketoconazole, fluconazole, or itraconazole.

Getting Canine Infections Diagnosed and Treated

If you think your dog might have a bacterial or fungal infection, you need to take him to the veterinarian for an examination as soon as possible.

About the Author

Dr. Evan Ware

Dr. Evan Ware is a veterinary practitioner in Phoenix, Arizona. He received both his undergraduate degree in microbiology and his Doctorate of Veterinary Medicine from The Ohio State University.

Dr. Ware is currently the Medical Director of University Animal Hospital (VCA) and is also the owner of two other hospitals, including Laveen Veterinary Center and Phoenix Veterinary Center. His areas of expertise include orthopedic medicine and surgery, veterinary oncology and chemotherapy, and general and advanced soft-tissue surgery.