Epidemiological survey of porcine reproductive and respiratory syndrome in scaled pig farms of Guangdong province

Objective  To investigate the prevalence of porcine reproductive and respiratory syndrome virus (PRRSV) in Guangdong province.

Method  From 2014 to 2016, totally 1 137 porcine tissue samples and 9 432 porcine serum samples were collected from scaled pig farms in Guangdong for antigen and antibody detection respectively. The results were compared among different years, seasons and regions. Phylogenetic analysis were performed on isolated viruses.

Result  From 2014 to 2016, the yearly positive rates of PRRSV antigens were 30.86%, 34.35% and 37.50% respectively, while the yearly antibody positive rates were 82.86%, 68.87% and 74.56% respectively. In quarterly analysis, the first quarter had the highest antigen positive rate of 40.27% and the second quarter had the lowest antigen positive rate of 28.66%. The antibody level of every quarter was above 70%. There were significant differences in PRRSV infection rates among different regions. The infection rates in eastern Guangdong and western Guangdong were significantly lower than those in the Pearl River Delta and northern Guangdong. The antibody positive rate was the lowest (69.51%) in eastern Guangdong and above 75% in the other three regions. A total of 69 PRRSV strains were isolated from samples with positive antigen, of which 39 strains belonged to Subgenotype I.

Conclusion  The antigen positive rate of PRRSV in Guangdong shows an increasing trend, while the antibody positive rate is relatively high but unstable. Subgenotype I is the predominant subgroup in Guangdong based on the virus isolation results.