Serologic profile of a cohort of pigs and antibody response to an autogenous vaccine for Actinobacillus suis

Actinobacillus suis is a commensal opportunistic pathogen in swine. However , in recent years, an increasing prevalence of clinical signs associated wi th A. suis has been observed in high health status herds in North America. The objectives of the study were to assess the kinetics of antibodies to A. suis in pigs from a herd showing clinical signs of A. suis infection and, to evaluate the antibody response in gilts following vaccination with an au togenous vaccine. An enzyme-linked immunosorbent assay (ELISA) using a sali ne extract of boiled-formalinized whole cells of a field strain as the coat ing antigen was standardized. This ELISA was used as a tool for monitoring, in a comparative way, the variations in A. suis antibody levels. The herd selected for the serologic profile was negative for Actinobacillus pleuropn eumoniae infection and showed clinical signs of A. suis infection in 16 to 19-week-old pigs. A cohort of 20 pigs was blood sampled at 5, 8, 12, and 16 weeks of age. The lowest level of serum antibodies was observed between we eks 8 and 12, this probably corresponding to a decrease in maternal immunit y. A marked increase in the antibody response was seen at 16-week of age, a t the approximate time of onset of A. suis clinical signs in the herd. The evaluation of serum antibody responses to an autogenous vaccine revealed th at the humoral immunity of gilts further increased following vaccination al though the level of antibodies was already high prior to vaccination. The m agnitude of the response to vaccination was higher when the level of antibo dies was low prior to the first injection. The ELISA test seems to detect a ntibodies against the O-chain LPS.