In vitro detection of neutralising antibodies to Chlamydia suis in pig sera.

In this study the in vitro neutralising activity of 71 pig sera resulted positive by MIF technique against Chlamydia suis has been evaluated: these samples were collected from 2004 to 2006 from pigs with clinical signs of conjunctivitis and/or reproductive disorders, reared in two different farms in Emilia-Romagna (Northern Italy). Neutralisation reactions using purified EBs of Chlamydophila abortus, Chlamydophila psittaci and Chlamydophila pecorum were performed to control the specificity of neutralising antibodies to C. suis. Twenty serum samples randomly collected in Emilia-Romagna in a farm from pigs without signs of conjunctivitis and reproductive problems were tested for the presence of neutralising antibodies, as a control. Neutralising antibodies specific to C. suis were present in 57 out of the 71 (80×3 per cent) pig sera resulted positive by MIF with titres ranging between 32 to 2048. The presence of neutralising antibodies was significantly correlated (p < 0×001) with MIF titres. Pig sera neutralising to C. suis EBs, tested against the EBs of Cp. psittaci, Cp. abortus and Cp. pecorum, did not show any neutralising activity against these three different chlamydial species. Control sera collected from pigs without clinical signs of conjunctivitis or reproductive disorders presented no neutralising activity to C. suis.