Seroprevalence and associated risk factors of pseudorabies in Shandong province of China

Abstract

A cross-sectional serological study was conducted in Shandong province of China to determine the seroprevalence and risk factors associated with seropositivity due to pseudorabies virus (PRV) infection in small- and medium-sized farrow-to-finish herds following outbreaks of variant PRV strains. A total of 6,035 blood samples from 224 randomly selected herds were screened. The results showed that 25.0% of the herds and 56.7% of the serum samples were seropositive for field strains of PRV. Herds consisting of 50-100 breeding sows had higher herd seroprevalence and serum sample seroprevalence than larger herds. Both the highest herd seroprevalence and highest serum sample seroprevalence were observed in western Shandong, followed northern Shandong. Based on univariate analysis, the following risk factors were utilized in subsequent multivariable logistic regression analysis: region, herd size, weight of purchased gilts, and all-in/all-out practice. Upon multivariate analysis, region, herd size, weight of purchased gilts and all-in/all-out practice were significantly associated with PRV herd seropositivity. These findings indicate that we are facing a serious situation in the prevention and control of pseudorabies. The results could help predict the next outbreak and set out control measures.

Keywords: Aujeszky’s disease; pseudorabies; risk factor; seropositivity; seroprevalence.

Fig. 1. Map of Shandong and its 17 cities. All of the selected farms where serum samples were collected are marked as black dots (2012), white dots (2013) and squares (2014). The five regions (east, E; west, W; south, S; north, N; central, C) are identified with different patterns.

Fig. 2. Seroprevalence of serum samples or herds in different regions classified by different herd sizes. (A) Sample seroprevalence. (B) Herd seroprevalence. Both sample seroprevalence and herd seroprevalence varied with herd geographical location, and they showed a similar tendency toward west > north > central > south > east. Among the different regions, the seroprevalence of 50‒100-sow herds, as well as the seroprevalence of samples collected from such herds, was highest in the north, while the seroprevalence of larger herds, as well as the seroprevalence of samples collected from such herds, was highest in the west.

Fig. 3. Sample seroprevalence of different production phases in the five regions. (A) Sample seroprevalence of fattening pigs. (B) Sample seroprevalence of gilts. (C) Sample seroprevalence of multiparous sows.