Haemophilus parasuis oligopeptide permease A (OppA) was identified by Western blot using swine convalescent sera.
Recombinant OppA (rOppA)-based ELISA is useful to track systemic infection against H. parasuis.
Immunization with H. parasuis rOppA protein had robust serological responses.
Antibodies to rOppA do not protect pigs against H. parasuis challenge.