Molecular Epidemiological Study of Porcine Epidemic Diarrhea from Winter 2020 to Spring 2021 in Jiangsu Province

Background: Porcine epidemic diarrhea (PED) is an acute and highly contagious infectious disease caused by the porcine epidemic diarrhea virus (PEDV) that occurs most frequently from winter to spring. It is associated with high morbidity and mortality rates, especially among piglets, and causes huge losses in the pig industry. The aim of this molecular epidemiological study was to identify the current strains of PEDV that are prevalent in Jiangsu Province, China.Methods: From winter 2020 to spring 2021, 793 small intestine tissue, fecal, and anal swab samples were collected from 72 pig farms in 11 counties in the jurisdiction of 5 regions of Jiangsu Province (Yancheng, Suqian, Changzhou, Xuzhou, and Yangzhou). A highly variable region of the S gene was amplified and sequenced, and phylogenetic analysis was conducted to compare this sequence with corresponding sequences from reference strains deposited in GenBank. Results: A total of 457 samples from 57 pig farms were positive for PEDV: this implies a positivity rate of 79% (57/72) for pig farms and a sample positivity rate of 57.6% (457/793). The positivity rates were 78% (107/137) in Yancheng, 53% (218/409) in Suqian, 48% (94/195) in Changzhou, 80% (16/20) in Xuzhou, and 88% (14/16) in Yangzhou. Seven representative samples were selected for sequencing, and phylogenetic analysis showed that the seven isolated strains exhibited 88.0%–100% nucleotide identity and 87.3%–99% amino acid identity. Additionally, our isolates exhibited 88.3%–99.7% nucleotide identity and 88%–98.5% amino acid identity with the reference PEDV strains. Phylogenetic tree analysis indicated that there were considerable difference in the sources of the variants.Conclusions: PEDV had a high infection rate among pigs and is possibly the main pathogenic agent of pig diarrhea in Jiangsu province. Importantly, vaccines must be screened for their efficacy against the newly identified variants.

Genetic Variability of PRRSV Vaccine Strains Used in the National Eradication Programme, Hungary

Porcine reproductive and respiratory syndrome (PRRS) is a globally spread, highly infectious viral disease. Live, attenuated vaccines against PRRS virus (PRRSV) decrease virus excretion and evoke protective immunity reducing the economic damage caused by the disease. In a longitudinal molecular epidemiological study accompanying ongoing national eradication programme we evaluated the suitability of PRRSV ORF5 and ORF7 sequences to identify possible field strains of vaccine-origin. In total, 2342 ORF5 sequences and 478 ORF7 sequences were analysed. Vaccine strains were identified by sequence identity values and phylogenetic network analysis. Strains that shared greater than 98% nucleotide identity within ORF5 and/or ORF7 were considered to have originated from vaccine. A total of 882 (37.6%) ORF5 and 88 (18.4%) ORF7 sequences met these criteria. In detail, 618, 179 and 35 ORF5 and 51, 29 and 8 ORF7 sequences were related to Porcilis PRRS vaccine, Unistrain PRRS vaccine, and ReproCyc PRRS EU vaccine, respectively. Data showed that the Porcilis vaccine was genetically more stable. Whereas, the variability of the Unistrain and the ReproCyc strains was significantly higher. Given that ORF7 shares, in some instances, complete identity between a particular vaccine strain and some historic variants of field PRRSV strains, care must be taken when evaluating vaccine relatedness of a field isolate based on the ORF7. On the contrary, ORF5 sequences were more suitable to predict the vaccine origin making a distinction more robustly between field and vaccine strains. We conclude that ORF5 based molecular epidemiological studies support more efficiently the ongoing PRRS eradication programmes. The conclusions presented in this large-scale PRRS molecular epidemiological study provides a framework for future eradication programmes planned in other countries.