Comparison of qPCR and blood smear microscopy for the diagnosis of Mycoplasma suis in a French veterinary practice

Mycoplasma suis (M. suis) is an haemotropic Mycoplasma that adheres and invades erythrocytes and is responsible for infectious anaemia of pigs. Infections with M. suis have been reported worldwide. Clinical signs after M. suis infection can be significant particularly for the breeding herd in the period around farrowing but consequences are highly variable with some infected pigs never exhibiting clinical disease. The study aimed to determine the clinical relevance of Giemsa-stained blood smear for the diagnosis of M. suis compared with qPCR results. In our study, the comparison of qPCR results with microscopic investigation of Giemsa-stained blood smears revealed a lower sensitivity of the microscopic method: only 33 out of 102 qPCR positive blood samples were microscopically positive (M. suis visualised). No relationship between mean qPCR loads and microscopic observation was observed. Although more costly, qPCR is probably the best diagnostic tool available today for M. suis diagnosis.