| Classical swine fever(CSF), caused by Classical swine fever virus(CSFV), is a highly contagious desease with the characteristics of fever, generalized haemorrhages and ichoremia, which leads to devastating economic losses when the disease outbreaks. CSF can infect all kinds of swine, Regardless of age, sex and breed. In recent years, the immunological failures of CSF were reported frequently and some new characters were presented in the popularity of CSFV, which is related to many causes, among them, probably including the genetic mutation of CSFV. So, in order to control CSFV effectively and reduce the economic losses, it is essential to carry out an epidemiological survey of CSF for better understanding of the epidemiological status of CSF and the genetic mutation of CSFV.Basis on the investigation of the health status of pig herds, the epidemiological surveys of CSF were taken in144pig farms including33pig breeding farms,50scale pig farms and61household pig farms which distributed to50counties belonging to17cities in Shandong province by means of questionnaire, field survey, cases diagnosis and detection of antibodies etc. the results showed that there were Phenomenons of Sow abortion, birth of a dead fetus and low survival rate of piglets.11241serum samples from242pig farms were detected for CSF immune antibodies, among them,6379samples were up to standard, the antidoies qualified rate was56.75%.93suspected CSF cases found in70veterinary clinics from2011.5to2012.8suggested that the CSF was still one of the main pig diseases which influenced the development of pig industry in Shandong province, and prevention and control of the disease should be strengthened.The IDEXX CSFV antibody and antigen test kit were used to detect the level of antibody and antigen of1080sera samples from8pig farms from July201ltoJuanary2012, in which1080sera samples from these16pig farms were used to detect the antibody level, others363sera samples from6pig farms with lower immunity level of antibody among these16farms were used to detect the virus infectious antigen. The results showed that the antibody positive rates against CSFV are43.28%-87.75%, and the antigen positive rates of CSFV antigen between0%-4.48%. It means that the immunological status of CSF in Shandong province is irregularity, Some of the pig farms show a low immunity level, and carries CSFV.In this study, a total of13samples from the farms with lower immunity level of CSF antibody were collected and detected by RT-PCR.8samples were found to be positive, which were inoculated into PK-15cells, subsequently,8CSFV strains were isolated and were named as SDWF、SDTA、SDCQ、SDDY、SDWH、SDZB、SDLC and SDZZ respectively. All the8strains were certified by real time RT-PCR that they all belonged to the epidemic field strains. The results further conformed that the immunized pig farms really carried CSFV. So, In order to prevent from infection of field CSFV strains, the antibody against CSFV should be tested regularly and appropriate measures be carried out to ensure high CSF antibody level.To research the homology and mutation analysis between strain SD and other reference stains, a phylogenetic tree was constructed using the entire Erns gene sequence of strains SD and others Erns genes.To reveal the characteristics of the protein encoded by Erns, its deduced amino acid sequence was further aligned with other12representative strains. Two conserved regions (CRs) which were similar with the fungal and plant RNases were located at aa28-36and75-82. The residue E was replaced with G between endemic strains and vaccine strains at the position36in the CR1. One interesting question is whether the switching of the positions altered the efficacy of the vaccine. It showed that the SD strains were clustered together in the subgroup1.1a which was represented by reference strains comprising of a German isolate (Paderborn), one Taiwan isolate and two Chinese isolates. |
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