The study executed a large-scale molecular epidemiological investigation of porcine epidemic diarrhea (PED) and five-yearlong monitoring of nine swine herds with the outbreak of diarrhea in south China. Porcine epidemic diarrhea virus (PEDV) exists all year round with varying degrees of mortality to suckling piglets, the highest mortality was in 2011 and followed by 2012, the lowest mortality was in 2013, with the mortality showed an increasing trend year by year during 2014 to 2015. It was noteworthy that the pregnant sows assumed the highest morbidity, followed by nursing sow while the nursed piglets and the growing pigs had lower morbidity. The current epidemic strains in south China were divided into two groups, Group 1 and Group 2 by generating the phylogenetic tree of thirty-five spike (S) genes during 2011-2015. Group 1 had 6.92-7.21% mutation rate while Group 2 owned 4.18% mutation rate when compared with CV777. The strains in Group 2 felled into the same branch with the previous Chinese isolates from 2004 while the strains in Group 1 had a close relationship with the United States strain. Interestingly, clinical morbidity caused by two types of PEDV strains were quite different, strains in G2-2 caused relatively minor mild clinical manifestations, presenting a smaller mortality and shorter onset period, while strains in G1-2 and G1-3 is caused by an outbreak of acute infectious diseases, showed a larger mortality and longer period especially PEDV strains in G1-3. It was also indicated that the effect way to prevent PEDV should focus on reduce the morbidity of pregnant sows.

Key words: Dynamic investigation, Porcine epidemic diarrhea virus, Spike gene