Screening Of Newly Inactivated Vaccine Strains Of Foot-and-Mouth Disease Type O

Foot-and-Mouth Disease (FMD) is a highly contagious disease of cattle, goats, pigs and sheep caused by foot-and-mouth disease virus (FMDV). It can be leding to great economic losses and political influence. FMDV belongs to the aphtovirus genus of the Picornaviridae family and variation easyly. Until now, the main strategy to prevent and control FMD is still the immunity vaccination internationally. There are many factors to affect inactivated vaccines, immunity potency. But speaking of the vaccine itself, the most crucial elements are selection of performance fine vaccine strains.In ordee to deal with FMDV mutation and overseas pestilence, enhance reliability and pointed of the immunoprophylaxis, it is necessary to screen newly-prepared vaccine strain at the right moment. It will provide the foundation material for development new FMD inactivated vaccine.In this study, we have screned newly-prepared vaccine strain from collected 5"Pan-Asia"strains of FMD type O through the etiology, the epidemiology and the immunology system research and analysis. Mostly research content and results are as follows:1. Five typical epidemic FMD type O strains which existed in different areas from 1999～2006 were collected. They were identified for"Pan-Asia"of FMDV type O by Reverse Indirect Hemoagglutination Test and cloning and sequencing VP1 gene. 5 strains were O/GSLT/06, O/NXZN/04, O/JXYJ/05, O/HNXH/00 and O/NX/99 respectively.2. A series of studies on the biological characteristics of the five typical epidemic strains were carried out. (1) All of the 5 FMD strains had good adaptability and high pathogenicity to suckling mice.After vaccinated suckling mice and passed 4 generation,the sunkling mice death time reduced within 27h. The LD50 of O/GSLT/06, O/NXZN/04, O/JXYJ/05, O/HNXH/00 and O/NX/99 were 10-7.5, 10-8.00, 10-7.33, 10-7.5 and 10-7.00 respectively. (2) All of the 5 FMD strains had good adaptability and high pathogenicity to BHK-21 cells. After BHK-21 cell serial passage, the time of each of the strains to lead CPE stablilized in 11～13h. The TCID50 of the strains were 10-6.33, 10-5.38, 10-5.08, 10-6.08 and 10-6.33 respectively. Relatively speaking, O/GSLT/06 were more superiority. It had better adaptability to BHK-21 and leaded CPE time was 11h. So it was hopeful to be vaccine strain.3. The nucleotide sequence of the VP1 gene were cloned, sequenced and analysised. Phylogenetic tree based on nucleotide sequence of the VP1 gene had been drawn. The analysis indicated that homology among the 5 strains were 92.8%～97.0% for nucleotide sequence, belong to the genotype"Pan-Asia"of the FMD type O. The amino acid of the five epidemic strains occurred variation at different sites and these sites are antigen sites.4. Each strain immunology characteristic comparison research indicated that each strain had the good immunogenic. But O/GSLT/06 was best and the antigen relations (r value) with other strains were close (the r value≥0.4). So it was hopeful to be backup FMD inactivated vaccine strain.