| Porcine epidemic diarrhea (PED), caused by porcine epidemic diarrhea virus (PEDV), is an acute and highly contagious disease in swine. The disease is characterized by severe enteritis and watery diarrhea. In China, PED was first reported in1976, then it occured frequently in swine-raising farms. Since the end of2010, piglets diarrhea has been prevailing in many provinces in China, resulting in heavy economic losses in swine industry. In this study, we proved PEDV variant strains were the main pathogens by etiological detection, ORF3gene molecular epidemiology and experimental challenge with piglets. The main contents are as following:1. Molecular epidemiology of porcine epidemic diarrhea virus based on the ORF3gene153diarrhea samples of suckling piglets were collected from47pig farms and PEDV was detected by RT-PCR. The results showed that88samples from26pig farms were positive. The farm positive rate was55.32%and the sample positive rate was57.52%.ORF3gene was cloned into pMD18-T vector and sequenced.The result of sequencing showed that the length of ORF3genes all were675bp which encoded224amino acids. The nucleotide homologies of the11strains were95.9%-99.9%and amino acid homologies were96.4%-100%. By comparing with those of European strain CV777vaccine strain CV777truncated and Korean strains, the nucleotide homologies were96.3%-97.0%,96.39-97.0%and95.0%-98.5%, respectively, and the amino acid homologies are95.1%-96.4%,96.8%-97.6%and95.5%-99.6%, respectively. The vaccine strain CV777truncated has a49-nt deletion at245-293, which is not found among the11strains. Based on the phylogenetic relationship of their ORF3genes, the PEDV field strains and PEDV reference strains could be divided into four groups. And most of Chinese PEDV field strains belonged to Group1and had a close phylogenetic relationship with Korean strains.But there were genetically different from the PEDV vaccine strains used in China. It suggested that, PEDV is one of the main pathogens of the diarrhea in suckling piglets, and the Chinese PEDV strains have a significant genetic variation.2. Pathogenicity of prevalent PEDV strains in pigletsAccording to the results of sequencing,3intestine samples which contained different prevalent PEDV strains were selected and infected orally, each with3piglets, respectively, while physiological saline was used as negative control.They were assigned to different rooms and feeded with milk every two hours. And clinical signs, gross lesions, microscopic lesions were observed and etiological detection were done in intestine samples of the piglets. The results showed that ZJ120101and ZJ120102could cause the typical PED in the piglets, including vomiting in a short time, yellow watery diarrhea and dehydration, and two piglets in the ZJ120101group were dead. Expand of the intestine filled with liquid, wall thinning also could be found by necropsy. Small intestine villus was significantly atrophied, epithelial cell loss and intestinal mucosa fold reduced were observed. However, the clinical signs, gross lesions and microscopic lesions of the infected pigs in AH110816strain group were mild and slight. The control group exhibited no clinical signs. PEDV could be detected in the ZJ120101, ZJ120102and AH110816gourps were positive. But PRRSV, PCV2, TGEV and PoRV could not be detected in all piglets at the end of the experiment. It demonstrated that different prevalent PEDV strains could induce PED in suckling piglets, but they had some differences in the pathogenicity in piglets. It should be helpful for preventing and controlling PEDV infection in the future. |
PDF Full Text Request