Porcine reproductive and respiratory syndrome (PRRS), caused by the PRRS virus, is one of the most important diseases in the pig production industry throughout the world (Scortti et al. 2006a; Zimmerman et al. 2006; Tummaruk et al. 2013). PRRS virus is an enveloped RNA virus that is divided into two genotypes, i.e. European (EU or type 1) and North American (NA or type 2) (Meng 2000).