Mycoplasma cynos is a species of atypical bacterium that can be a complicating factor in the health of domestic dogs. This organism is commonly present in the upper respiratory tract of healthy animals, existing as part of the normal microbial community without causing any problems. However, under certain conditions, this bacterium can transition from a benign resident to an opportunistic pathogen, leading to infectious disease. When it becomes pathogenic, M. cynos is often associated with issues in the canine respiratory system and, less frequently, the joints.
The Organism and Its Canine Hosts
The genus Mycoplasma is distinct among bacteria because its members do not possess a rigid cell wall. This lack of a cell wall means they are highly flexible. M. cynos and related species rely on the rich, protected environment of mucosal membranes, such as those lining the respiratory and urogenital tracts, for growth and survival.
While many healthy dogs carry M. cynos in their upper airways, the organism poses the greatest threat to specific populations of dogs. Animals with compromised immune systems, very young puppies, and older dogs are most susceptible to developing clinical disease. Furthermore, dogs already suffering from other infections, particularly those involved in the Canine Infectious Respiratory Disease Complex (CIRDC), are at higher risk.
How Mycoplasma Cynos Causes Disease
The disease process initiated by M. cynos begins when the organism attaches to the host’s cells lining the respiratory passages. This attachment is followed by localized inflammation and damage, which can lead to the destruction and loss of the tiny, hair-like structures responsible for clearing mucus and debris from the lungs. This damage impairs the dog’s natural defense mechanisms, making the respiratory tract vulnerable to secondary infections.
M. cynos frequently acts as a co-pathogen. It works alongside other viruses or bacteria already present in the dog’s system. Damage to lung tissue caused by viral infections can promote the colonization of the lower respiratory tract by Mycoplasma, often leading to more severe and prolonged illness.
When the respiratory tract is affected, common signs include a persistent cough, inflammation of the nose (rhinitis), and sometimes serious lower respiratory tract infections like pneumonia. Less commonly, the infection can spread beyond the respiratory system, resulting in signs like polyarthritis, which is characterized by joint pain and swelling. Other generalized symptoms may accompany the infection, such as lethargy, a decreased appetite, and an elevated body temperature.
Confirming the Diagnosis
Diagnosing an infection caused by M. cynos can be a complex process. Since this bacterium is a normal resident in many healthy dogs, simply detecting its presence does not confirm it as the sole cause of the illness.
Traditional bacterial culture methods are often inadequate for identifying Mycoplasma species due to their fastidious growth requirements and fragile nature. The preferred and most reliable diagnostic method is the Polymerase Chain Reaction (PCR) test. PCR offers high sensitivity and specificity, allowing for the accurate identification of M. cynos.
Samples for PCR testing are collected from the site of the suspected infection. These may include swabs from the nasal or throat areas, or more invasive samples like a tracheal wash or bronchoalveolar lavage (BAL) for lower respiratory disease. If joint involvement is suspected, a fluid sample from the affected joint (synovial fluid) can be tested. This targeted testing helps confirm the organism’s role in the disease, particularly when it is isolated from a normally sterile site.
Treatment and Recovery
The lack of a cell wall in Mycoplasma species dictates the choice of antimicrobial therapy. Many common antibiotics, such as penicillin-based drugs, are ineffective because they work by destroying the bacterial cell wall. Effective treatment requires specific classes of antibiotics that penetrate the bacterial cell membrane or interfere with protein synthesis.
The first-line treatment choice for M. cynos infections is typically a tetracycline-class antibiotic, such as doxycycline. In cases where doxycycline is not appropriate or if the infection is particularly severe, a veterinarian may consider using a fluoroquinolone-class antibiotic as a second-line option. Treatment for respiratory infections usually requires a minimum course of two weeks, but for more serious conditions like pneumonia, the medication may need to be administered for four weeks or longer.
Supportive care is often administered to manage the dog’s symptoms while the antibiotics take effect, which may include medications to control fever or nebulization therapy for severe respiratory signs. The prognosis for dogs with M. cynos infection is generally favorable when the condition is diagnosed early and treated with the appropriate course of antibiotics. However, delayed treatment or the presence of a severely compromised immune system can lead to chronic respiratory issues or a prolonged recovery period.