Since its discovery in the early 1990s , tremendous progresses have been made in understanding the molecular biology and pathogenesis of PRRSV .
the disease remains difficult to control .
Since its discovery in the early 1990s , tremendous progresses have been made in understanding the molecular biology and pathogenesis of PRRSV .
Although modified live - attenuated vaccines ( MLVs ) and inactivated vaccines against PRRSV have been available for more than a decade , the disease remains difficult to control .