| An epidemic that mainly endangered 3-7-day-old piglets struck many farms in Shandong Province, China in 2013 and caused heavy losses. To identify the pathogenesis, the type of lesions, and the causative agent, systemic examinations were performed. Postmortem examination showed multiple lesions, including necrotic foci of the spleen and liver, punctate hemorrhage of the renal cortex, and interstitial pneumonia. Histological examinations showed typical nonsuppurative encephalitis, necrotic lymphocytes, and reticuloendothelial cells in lymphatic tissues, as well as eosinophilic inclusion bodies in the nuclei of reticuloendothelial cells, necrotic foci in liver cells, and hemorrhagic glomeruli. The average seroprevalence rate of wild-type pseudorabies virus of a representative farm tested by enzyme-linked immunosorbent assay was 46%, indicating that the PRV infectious pressure was quite severe especially among gilts, young multiparous sows, boars, and growing-finishing pigs. The glycoprotein E (gE) gene of PRV was detected in 8 of 10 clinical samples, and the virus in the positive samples induced obvious cytopathic effects. An immunoperoxidase monolayer assay showed that PRV antigens were distributed both in the nucleoli and cytoplasm of infected cells. Sequencing and phylogenetic analysis of the gE gene showed that the strain isolated herein, TaiAn SD 2013, was highly similar to previously isolated strains, especially those isolated in northern China in 2013, and was closely related to other isolates from Asia. Evidence confirmed that the variant PRV was the etiologic agent of this epidemic, suggesting that the Bartha-K61 vaccine does not provide complete protection against PRV infection. Further challenge tests are ongoing to investigate the virulence of variant PRV. Furthermore, 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 infection in small- and medium-sized farrow-to-finish herds following the outbreak of a PRV epidemic in late 2011. A total of 224 randomly selected herds and 6,035 corresponding blood samples 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 and serum sample seroprevalences than larger herds. Both the highest herd and serum sample seroprevalences were observed in western Shandong, followed by those in northern Shandong. Based on a univariate analysis, risk factors that were offered to the subsequent multivariable logistic regression analysis were as follows:region, herd size, weight of purchased gilts, and all-in/all-out practice. In a multivariate analysis, region, herd size, weight of purchased gilts and all-in/all-out practice were significantly associated with PRV herd seropositivity. The results indicated that we are facing a serious situation in the prevention and control of PR, and the results could help to predict the epidemic and set out control measures. |
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