Prevalence of Mycoplasma synoviae in broilers, hobby poultry and wild birds in Belgium

Mycoplasma synoviae has during many years been considered a less important pathogenic species for poultry than Mycoplasma gallisepticum, causing subclinical respiratory infections in broilers. However, the importance of this bacterium and its relevance from a clinical and economic viewpoint has increased since M. synoviae arthritis, amyloid arthropathy, and eggshell apex abnormalities have been reported. Because of vertical transmission of mycoplasma species, there is an official eradication program for M. gallisepticum in breeder stock. Since the implementation of such a program, a decreasing incidence of M. gallisepticum has been observed. However, for M. synoviae, there is currently no such eradication program which may be a cause of dissemination from breeder stock into layer and broiler holdings. During a prevalence study on M. gallisepticum in Belgium, data on presence of M. synoviae in broiler holdings, backyard flocks and wild birds was also gathered. A random selection of poultry herds, proportional to herd density per province, was made based on the active holdings present in the Belgian National Animal Identification and Registration System (Sanitel) data base owned by the Federal Agency for the Safety of the Food Chain (FASFC). At each broiler holding (n=102) 12 tracheal swabs were collected and analysed using a commercial real-time PCR kit (ADIAVET™ Myco AV, Biomérieux). Fifty-six owners of backyard chickens (n=460) were visited and of each owner maximum 10 chickens were sampled. Tracheal swabs from wild birds (n=100) were collected by hunters during hunting season of September – January 2013; and three bird rescue centers were visited and tracheal swabs (n=90) were taken from different species of wild birds common in Belgium. All tracheal swabs were analyzed with RT-PCR (ADIAVET™ Myco AV, Biomérieux). Twenty-seven broiler holdings (26.5%; 95% CI: 18.9-35.8%) tested positive for M. synoviae with a within herd prevalence of 48.8% (95% CI: 43.4-54.2%) and 158 out of 1224 tracheal swabs (12.9%; 95% CI: 11.1-14.9%) were M. synoviae positive. Fifty-four out of 56 owners of backyard chickens had positive flocks resulting in a seroprevalence of 96.4% (95% CI: 87.9-99%) of backyard flocks with a within flock prevalence of 78% (73.9-81.6%). Three hundred and fifty-one out of 460 tracheal swabs (76.3%; 95% CI: 72.2-80%) were positive for M. synoviae. Four samples (one crow and three wood pigeons) obtained during hunting season (4%; 95% CI: 1.6-9.8%) tested positive for M. synoviae. Three samples (one peacock pigeon and two wood pigeons) out of 90 tracheal swabs collected in bird rescue centers (3.3%; 95% CI: 1.1-9.3%) were M. synoviae positive. The prevalence of M. synoviae in broilers is high which could be related to the lack of eradication programs and the possibility of vertical transmission from breeder stock into commercial poultry holdings. In backyard chickens the seroprevalence of M. synoviae is extremely high which indicates that they may act as reservoir for this bacterium from which dissemination to poultry holdings is possible. Further analysis on samples from wild birds in bird rescue centers is ongoing and isolation and typing of strains will be used to determine the possible routes of transmission.