Porcine reproductive and respiratory syndrome virus (PRRSV) causes a highly contagious disease that threatens the global swine industry. Recent studies have focused on the damage that PRRSV causes to the reproductive system of male pigs, although pathological research is lacking. Therefore, we examined the pathogenic mechanisms in male piglets infected with PRRSV. Gross and histopathological changes indicated that PRRSV affected the entire reproductive system, as confirmed via immunohistochemical analysis. PRRSV infected Sertoli cells and spermatogonia. To test the new hypothesis that PRRSV infection in piglets impairs blood – testis barrier (BTB) development, we investigated the pathology of PRRSV damage in the BTB. PRRSV infection significantly decreased the quantity and proliferative capacity of Sertoli cells constituting the BTB. Zonula occludens-1 and β-catenin were downregulated in cell – cell junctions. Transcriptome analysis revealed that several crucial genes and signalling pathways involved in the growth and development of Leydig cells, Sertoli cells, and tight junctions in the testes were downregulated. Apoptosis, necroptosis, inflammatory, and oxidative stress-related pathways were activated, whereas hormone secretion-related pathways were inhibited. Many Sertoli cells and spermatogonia underwent apoptosis during early differentiation. Infected piglets exhibited disrupted androgen secretion, leading to significantly reduced testosterone and anti-Müllerian hormone levels. A cytokine storm occurred, notably upregulating cytokines such as tumour necrosis factor-α and interleukin-6. Markers of oxidative-stress damage (i.e. H
2
O
2
, malondialdehyde, and glutathione) were upregulated, whereas antioxidant-enzyme activities (i.e. superoxide dismutase, total antioxidant capacity, and catalase) were downregulated. Our results demonstrated that PRRSV infected multiple organs in the male reproductive system, which impaired growth in the BTB.
