Bacterial Infection (Mycoplasma) in Dogs

Mycoplasmas are a large family of gram-negative bacteria that lack a cell wall. They are considered to be the smallest form of life capable of reproducing (as opposed to viruses). Many species of mycoplasma are commensal, meaning they live in other organisms without either hurting or harming them, but others cause infection especially when they are able to proliferate in large numbers. There are hundreds of species of mycoplasma. They cause disease in many different animals, including dogs and humans, but species are typically host specific. At least fifteen different species have been identified in dogs. Mycoplasmas are commonly associated with the canine infectious respiratory disease (CIRD), also known as kennel cough. They are just one of a number of different organisms responsible for CIRD. Mycoplasma infection in the respiratory tract weakens a dog, increasing susceptibility to bacterial and viral infection. In many cases, it can be hard to tell which organism is the primary cause. Most studies show that mycoplasmas live in the upper respiratory tract of healthy dogs, but when they descend into the lower respiratory tract they cause infection and even pneumonia in severe cases. Mycoplasmas are also found in the genitourinary system in dogs; species that affect this area are categorized under the separate heading ureaplasmas. As in the respiratory system, ureaplasmas are part of the normal bacteria flora that colonize in healthy dogs, but under conditions of stress or immune-suppression they can proliferate and cause lesions that lead to infertility. Additionally, species of mycoplasma can attack red blood cells and cause anemia. These are called hemitropic mycoplasmas or hemoplasmas. They are transmitted through ticks and parasites, or dog to dog via blood transfusions or other methods of fluid exchange. They rarely cause symptoms in healthy dogs, but pets with a compromised immune system can develop severe hemolytic anemia and other symptoms of ill health.

Mycoplasmas are groups of very small bacteria that lack a cell wall. Some species can cause an infection called mycoplasmosis in dogs. Respiratory symptoms are the most common, but the bacteria can also affect the reproductive and urinary systems, and blood pathogens may cause anemia. Kennel dogs and dogs with weakened immune systems are more at risk.

Symptoms can vary depending on where the bacteria are located. These are some of the signs you might notice in your dog.

• Sneezing
• Coughing
• Inflammation of the nose (rhinitis)
• Eye inflammation (conjunctivitis)
• Fluid build-up and discharge from the eyes
• Difficulty breathing (pneumonia)
• Infection in the bladder, urinary tract or vagina
• Infertility
• Joint disease (polyarthritis)
• General systemic illness (weight loss, fever)
• Neurological symptoms (meningoencephalitis)

Types

These are some of the different types of mycoplasma that might relate to your dog’s diagnosis.

• Mycoplasmas species most commonly identified in dogs (mycoplasma canis, mycoplasma cynos)
• Acholeplasmas – a slightly different category of mycoplasma, one species has been identified in dogs called acholeplasma laidlawii
• Ureaplasma – a number of different species found specifically in the urinary tract
• Hemoplasmas – a blood mycoplasma that causes anemia
• Mycoplasma haemocanis – the hemoplasma most commonly found in dogs

Mycoplasmosis is an opportunistic disease that is influenced by your dog’s overall health as well as exposure to the bacteria.

Exposure to the bacteria

• Contact with sick dogs
• Staying in a kennel or shelter (especially long term)
• Possible air contamination with M. cynos (found in one study)
• Mating with infected dogs
• Blood transfusion
• Blood exchange during fighting

Dog’s overall health

• Infection with another bacteria or virus
• Infection with several species of mycoplasma at the same time
• Immune system suppressed from another treatment (chemotherapy or medication for an autoimmune disorder)
• Splenectomy
• Any long term disease

The veterinarian will analyze your dog’s symptoms as well as testing for the presence of mycoplasma in cultured samples. Respiratory symptoms are nonspecific, so it is difficult to tell if CIRD is caused by mycoplasma or another organism. Other symptoms such as urinary tract or genital infection will produce different symptoms. If your dog is experiencing generalized symptoms of illness or malaise, blood work may show anemia. Joint pain and lameness can also suggest more systemic mycoplasmosis. Any other factors, like other diseases, medications that suppress the immune system, or a recent stay at a kennel can be relevant.

It is not very easy to test for different species of mycoplasma because of their small size, and also difficulties with preserving and culturing the bacteria. M. canis and m. cynos can be identified with quantitative PCR testing, but other species may be harder to differentiate. A general diagnosis of mycoplasma may be given rather than an identification of specific species.

Other tests will focus on ruling out different causes for your dog’s symptoms. Bloodwork and urinalysis will be necessary. The veterinarian will also test for other bacterial and viral infection as these are commonly concurrent with mycoplasmosis. 

Mycoplasma do not respond to traditional beta-lam antibiotics (such a penicillin) because these drugs work by destroying the cell wall. However many tetracycline type antibiotics can be effective and doxycycline is frequently prescribed. The antibiotic will need to be taken for at least two weeks with an upper respiratory infection, and longer if your dog has lower respiratory symptoms or pneumonia. The veterinarian will prescribe an appropriate antibiotic dosage based on your dog’s symptoms. It’s important to continue treatment even after the symptoms have stopped in order to ensure that all the bacteria are killed and do not become resistant. Any immunosuppressant medication will need to be discontinued if possible to ensure the effectiveness of the antibiotic. Dogs with severe hemolytic anemia may need blood transfusion or glucocorticoids.

In most cases, dogs will make a complete recovery. Antibiotic treatment is typically effective, however dogs with hemoplasmas will still remain carriers after treatment. They can transmit the disease to other dogs and may experience clinical relapse occasionally. This condition is much easier to treat in the early stages, so it’s a good idea to make sure your dog has regular check-ups.

Mycoplasma can be managed most effectively by practicing proper hygiene and keeping your dog in good health. Avoid conditions of over-crowding, regularly clean out any kennels, wash and change bedding. Prompt treatment for infected animals can avoid spreading the disease. Make sure your dog has a healthy diet. Vitamins and supplements can sometimes help to support the immune system, so discuss the best choices with your veterinarian.