Impact of PRRSV strains of different in vivo virulence on the macrophage population of the thymus.

•The impact of PRRSV strains of different virulence on thymic macrophages was examined.•Animals died 10–14 days after PR40 or PR11 infection showed the most severe lesions.•The number of N-protein+, CD172a+, CD163+ and BA4D5+ cells increased at 10–14dpi.•No marked differences were observed between the PR11 and PR40 strains in this study.•Vaccination restrained virus spread and lesions in thymus of PR40-infected animals.