CTTNBP2 and infection: In contrast, ORF3 and ORF4 transcripts, which are not included in the above nine RNAs, were subsequently confirmed to play important roles in the pathogenesis of PCV2; ORF3-deficient PCV2 is attenuated in its natural host [28], and ORF4-deficient PCV2 induces a higher viral load and more severe microscopic lesions in the spleen during early stages of infection in mice [24].