Cleavage of the pp1a and pp1ab polyproteins by multiple intrinsic protease activities, in combination with −1 and −2 frameshifting in the nsp2 coding region in most arteriviruses with the exception of equine arteritis virus (EAV), results in the production of 13 to 17 non-structural proteins (nsps) (Fang et al., 2012; Li et al., 2014b; Ziebuhr et al., 2000) .