M synoviae was first recognized as an acute to chronic infection of chickens and turkeys that produced exudative tendinitis and synovitis (infectious synovitis), with increased condemnation in the processing plant due to airsacculitis, tendinitis and synovitis. Disease occurs most commonly as a subclinical infection of the upper respiratory tract.
M synoviae infection can lead to airsacculitis with or without the involvement of other respiratory pathogens like Newcastle disease virus or infectious bronchitis virus.
M synoviae is distributed worldwide and causes infection primarily in chickens and turkeys; however, ducks, geese, guinea fowl, parrots, pheasants, and quail may also be susceptible. M synoviae is even more fastidious than M gallisepticum; therefore, serum (preferably swine) and nicotinamide adenine dinucleotide (NAD) are required for growth of M synoviae in culture media.
M synoviae isolates vary widely in virulence, and suspected virulence factors include adhesins, sialidase, nitric oxide, cell invasion, and antigenic variation and immune evasion.
Epidemiology and Transmission of Mycoplasma synoviae Infection in Poultry
Mycoplasma synoviae is egg-transmitted (transovarian).
Horizontal transmission between farms is mainly by human activity on fomites (shoes, equipment, etc) or movement of infected acute or chronic carrier birds.
Once M synoviae is introduced into a flock, vertically or horizontally, clinical signs in the flock can be latent for days to months. However, when birds are stressed, direct horizontal transmission between birds within a flock often occurs rapidly via aerosols and respiratory secretions, after which clinical signs of disease spread through the flock.
Once individuals or flocks are infected, they remain infected for life and act as carriers or reservoirs of M synoviae.
Incidence of M synoviae infection in commercial poultry in the US has decreased because of the National Poultry Improvement Plan control programs implemented for chicken and turkey breeders. However, from time to time, large outbreaks occur, involving breeder and market birds, typically limited to one or a few states and related to one especially virulent isolate.
M synoviae infections of multiple-age layer flocks are common and may contribute to decreased egg production.
Clinical Findings and Lesions of Mycoplasma synoviae Infection in Poultry
Although slight rales may be present in birds with M synoviae respiratory infection, clinical signs are not usually noticed. However, birds under stress or with concurrent infections are more likely to show clinical signs.
The first clinical signs of infectious synovitis in many birds include pale-bluish head parts and lameness, with a tendency to sit. The more severely affected birds are depressed and found resting around feeders and drinkers. Hocks and footpads are swollen, and sternal bursitis (breast blisters) may occur (see image of infectious synovitis, chicken).
Courtesy of American Association of Avian Pathologists.
Morbidity is usually low to moderate with a mortality rate of 1–10%.
Similar to M gallisepticum, clinical signs of M synoviae infection are more pronounced and more associated with joint lesions in turkeys. Early in infectious synovitis, a creamy to viscous yellow-gray exudate is present in most synovial structures but is most commonly present in swollen hock and wing joints (see images of turkeys with swollen hock joint and swelling with exudate). In chronic cases, this exudate may become inspissated, and birds may be weak and thin with breast blisters from sternal recumbency. Effects on egg production are usually not apparent; however, instances of transient egg production drops have occurred in layer flocks. M synoviae has been reported to cause eggshell abnormalities (thin, translucent shell with abnormal apex) in egg layers, particularly in Europe.
Courtesy of Dr. Mohamed El-Gazzar.
Courtesy of Dr. Mohamed El-Gazzar.
Respiratory lesions may be absent or consist of mild mucoid tracheitis or sinusitis with airsacculitis when birds are stressed from poor air quality or challenged with Newcastle disease or infectious bronchitis.
Diagnosis of Mycoplasma synoviae Infection in Poultry
Real-time PCR assay
To diagnose M synoviae infection, skeletal abnormalities and trauma must first be eliminated as the cause of lameness.
Differential diagnoses include viral tenosynovitis, staphylococcal and other secondary bacterial joint infections, and other respiratory pathogens, such as Newcastle disease virus, infectious bronchitis virus, and M gallisepticum.
A presumptive diagnosis based on clinical signs and gross lesions should be confirmed by laboratory tests.
Serum plate agglutination or ELISA is used to detect M synoviae antibodies; however, cross-reactions with M gallisepticum and other nonspecific reactions may occur. These reactors are confirmed as seropositive by hemagglutination-inhibition assay or by isolation and identification of the isolated Mycoplasma colonies.
PCR assay may be used to rapidly detect M synoviae DNA from ante- or postmortem samples or from isolated colonies.
In turkeys, the agglutination test for M synoviae may not be reliable, especially in birds with predominantly respiratory infection.
Because of the fastidious nature of M synoviae and the difficulty of isolation, molecular diagnostic tests are commonly used for detection and characterization of Mycoplasma infections in poultry. Real-time PCR assay is a sensitive, specific, and fast detection test for M synoviae and can be performed directly on clinical swabs taken from infected sites (eg, choana, sinuses, trachea, air sacs, and joints). Sequence typing by targeting and amplifying specific genetic segments allows for differentiation between M synoviae isolates and outbreaks and can be particularly useful for epidemiological investigations and for identifying the source of infection.
Treatment, Control, and Prevention of Mycoplasma synoviae Infection in Poultry
Stock should be obtained from M synoviae–free breeding sources.
Good biosecurity helps control disease.
Antimicrobials in feed may help decrease synovitis but are not effective in established cases.
The National Poultry Improvement Plan coordinates control and serology-based surveillance programs for M synoviae similar to those for M gallisepticum. These programs have resulted in eradication of M synoviae infection in most primary breeder flocks of chickens and turkeys in the US. Chicks and poults should be obtained from M synoviae–free breeders and raised with biosecurity to prevent introduction.
Antimicrobials in feed may be beneficial in prevention of synovitis but are expensive and not very effective in established cases. When M synoviae involvement in airsacculitis is an anticipated problem, preventive antimicrobial therapy during the time of respiratory reaction to Newcastle disease and infectious bronchitis vaccines may be helpful.
A live, temperature-sensitive vaccine (MS-H) is available in many countries but not commercially available in the US. Availability of M synoviae–inactivated bacterins is becoming increasingly limited.
Key Points
M synoviae infection can be transmitted vertically and horizontally.
Once infected, individuals and flocks become chronic carriers (reservoirs).
Clinical signs caused by M synoviae are mild if uncomplicated, with low mortality rates and small drops in egg production; disease is more severe in turkeys and known as infectious synovitis.
Bacterial isolation, serological testing, and molecular diagnostic tests are commonly used in detection and characterization of M synoviae.
M synoviae–free breeding stocks are the method of choice for prevention.
For More Information
Ferguson-Noel N, Noormohammadi AH. Mycoplasma synoviae. In: Swayne DE, ed. Boulianne M, Logue CM, McDougald LR, Nair V, Suarez DL, associate eds. Diseases of Poultry. 14th ed. Wiley Blackwell; 2020:924-929.
Kempf I. Avian mycoplasmosis. In: Brugère-Picoux J, Vaillancourt J-P, Shivaprasad HL, Venne D, Bouzouaia M, eds. Manual of Poultry Diseases. Association francaise pour l’avancement des science; 2015:278-285.
