Diagnosis and gI antibody dynamics of pseudorabies virus in an intensive pig farm in Hei Longjiang Province

BACKGROUND: Pseudorabies (PR), caused by the pseudorabies virus (PRV), is an endemic disease in some regions of China. Although there are many reports on epidemiological investigations into pseudorabies, information on PRV gI antibody dynamics in one pig farm is sparse. OBJECTIVES: To diagnose PR and analyze the course of PR eradication in one pig farm. METHODS: Ten brains and 1,513 serum samples from different groups of pigs in a pig farm were collected to detect PRV gE gene and PRV gI antibody presence using real-time polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. RESULTS: The July 2015 results indicated that almost all brain samples were PRV gE gene positive, but PRV gI antibody results in the serum samples of the same piglets were all negative. In the boar herd, from October 2015 to July 2018 three positive individuals were culled in October 2015, and the negative status of the remaining boars was maintained in the following tests. In the sow herd, the PRV gI antibody positive rate was always more than 70% from October 2015 to October 2017; however, it decreased to 27% in January 2018 but increased to 40% and 52% in April and July 2018, respectively. The PRV gI antibody positive rate in 100-day pigs markedly decreased in October 2016 and was maintained at less than 30% in the following tests. For 150-day pigs, the PRV gI antibody positive rate decreased notably to 10% in April 2017 and maintained a negative status from July 2017. The positive trend of PRV gI antibody with an increase in pig age remarkably decreased in three tests in 2018. CONCLUSIONS: The results indicate that serological testing is not sensitive in the early stage of a PRV infection and that gilt introduction is a risk factor for a PRV-negative pig farm. The data on PRV gI antibody dynamics can provide reference information for pig farms wanting to eradicate PR.