- PRRSV is responsible for the worsening of the PCV2-related lesions and the enhancement of PCV2 DNA in the serum and of the PCV2 antigen in the tissue. - PRRSV and Mhp could damage the immune cells, thereby causing immunomodulation and triggering immunopathologies. - A pre-infection with PRRSV deteriorates the cytotoxic effects of bacteria on the cells. The gene discussed is CACNA1A; the disease is infection.