| Porcine epidemic diarrhea (PED) is a highly contagious, enteric disease of swine characterized by vomiting, dehydration,and a high mortality in piglets. The pigs of all ages are susceptible, but the most serious morbidity and mortality of piglets. The disease has been found in many countries including China, and has become one of the important diarrheal disease caused by the early death of piglets. The S protein of PEDV is a glycoprotein localized on the virion surface, which plays an key role in specific receptor binding and cell membrane fusion, and also is a major immune proteins in the induction of the neutralizing antibodies, in the case of PEDV, the ORF3gene is the only accessory gene, and it has been suggested to be an important determinant for virulence of this virus by restriction fragment length polymorphism analysis of ORF3genes between the highly cell-adapted viruses and field viruses. Therefore, it is great significance for finding out molecular characteristics of the pandemic strain to investigate the genetic diversity of S and ORF3genes at now.In the present study, an accurate diagnosis has been made for nineteen pig farms in eleven cities that outbroke virus-associated diarrhea in pigs on the base of clinical diagnosis, PCR detection, and eight of them were identified as PEDV infected city. Although swine of all ages are susceptible to this viral infection, the mortality in piglets under4weeks is commonly observed. The outbreaks usually occur during the winter as well as the early spring, and the major clinical signs can be observed as severe watery or yellowish diarrhea.ORF3and the partial S gene sequences of eight PEDVs isolates were amplified from the fecal samples by RT-PCR in Sichuan. The results showed that the ORF3gene of eight PEDV strains was675bp, encoding an open reading frame (ORF) with224amino acids; the partial S gene of eight PEDV strains was981bp, encoding a334-amino acid protein. Nucleotide and amino acid sequence analysis showed that recent, the eight strains of PEDV have17amino acids more than attenuate DR13, amino acid changes may induce PEDV strain’s virulence, then made swine disease serious and Increased mortality. The eight PEDV strains have higher homology with each other(Besides SCMY-S) in2011-2012, and also have higher homology with the strains isolated from many other provinces of China in recent years. SCMY-S’s nucleotide insertion and a large number of amino acid mutations caused by the change of antigen sites and characteristic of molecular biology will subject to our further research. Phylogenetic analysis indicated that ORF3gene showed two branches in the genetic evolution, which is significantly related to virulence. The eight PEDV strains were close to velogenic strain and distant with the attenuated DR13strain. The partial S gene of PEDV in genetic evolution can be divided into three branches, In recent years (2007-2012), the PEDV isolates separated from China, South Korea and Japan are in a big branch, which were distant with the early strain of France and korea. Among them, the eight PEDV strains were close to domestic strains and distant with foreign strains. Sequencing and analysis in this study, the regular of genetic evolution has been made clear, It will provide theoretical basis for accurate diagnosis and effective prevention of the disease, and will enrich the data of the molecular epidemiology of PEDV. |
PDF Full Text Request