Prevalence of Mycoplasma suis in slaughter pigs, with correlation of PCR results to hematological findings

Porcine infectious anemia is a well-known disease that occurs worldwide and is caused by the unculturable hemotrophic bacterium Mycoplasma suis. The actual prevalence and impact of M. suis infections, however, remain fairly unknown. This study examined the prevalence of M. suis in post-weaning pigs by employing a quantitative real-time LightCycler PCR. M. suis infections were detected in 164 out of 1176 feeder pigs (20–30 kg; 13.9%) as well as on 79 out of 196 pig farms (40.3%). The comparison of PCR results with microscopic investigation of acridine-orange-stained blood smears revealed a considerably lower sensitivity of the microscopic method: only 35 out of 1176 blood smears were microscopically positive. The microscopic detection of M. suis was shown to be closely linked to the bacterial load in the blood. M. suis infection is associated with significantly decreased hematocrit, erythrocyte counts and hemoglobin concentrations as well as significantly higher bilirubin concentrations. Furthermore, M. suis blood loads were significantly associated with erythrocyte count, hematocrit, hemoglobin, glucose and iron concentrations indicating that high M. suis loads are connected with clinical anemia. In conclusion, this study has shown, that M. suis infections are often under-diagnosed in pig husbandry and can therefore lead to considerable economic profit losses in pig husbandry. Furthermore, our study has shown that the LightCycler PCR could be an appropriate tool for a sufficiently coherent identification of M. suis in latent carrier animals in view of introducing effective treatment and disease control measures.