Since the genotypes of PRRSV-1 and PRRSV-2 share only about 70% at the nucleotide level [5], and GP5 is the most variable envelope protein with only ~50% amino acid homology between PRRSV-1 and PRRSV-2 strains [59, 60], we performed the same experiments described above using a PRRSV-1 isolate (Leystad) to analyse the role of N-glycosylation on viral infection. Here, ERVW-1 is linked to viral infectious disease.