Pathogeny or gE-Ab investigation of pseudorabies(PR),classical swine fever(CSF),porcine reproductive and respiratory syndrome(PRRS),porcine circovirus type 2(PCV2) showed that there were serious co-infections in farms of Guangdong from 2003 to 2004.There was a positive relation(P=0.012)between PR and PCV2,and the correlation coefficient was 0.648.This two disease were coinstantaneous in cross-spectrum analysis.There was weak connection between PCV2 and CSF.Prevalence of PCV2 will affect weakly on prevalence...