Epidemiological Survey Of CSFV In Guangdong And Comparison Of Immune Efficacy Between Classical Swine Fever E2 Protein Subunit Vaccine And C Strain Attenuated Vaccine

Classical swine fever is a contact-type infective disease caused by classical swine fever virus.It is also called"scar-intestinal fistula"in China.Swine is the only host of the disease.Character symptoms of CSF include high fever,hemorrhage,leukopenia and thrombocytopenia.CSF is highly transmissible and has a high fatality rate in infected pigs.It is listed as a notifiable disease by Office international des epizooties.In China,CSF is listed as class A animal disease and compulsory vaccination.Tissue materials from pig farms in Guangdong province were collected from January2017 to December 2017 for research of CSF in Guangdong province.RT-PCR were used to detect the virus and PK-15 cells were inoculated if positive sample were found.Two CSFV was successfully isolated and named GD02 and GD19.Sequencing of the E2 gene revealed that strain GD02 belongs to 2.1b subtype and GD19 belongs to 2.1g subtype.Acidity comparison showed that the homology between the GD02 and the classical strains was79.8%～94.2%,among which the homology with GXWZ02 strain was 94.2%;the homology with LPC strain was 79.8%;The attenuated vaccine strain HCLV homology was 80.4%.On the other hand,homology between the GD19 and the classical strains was 80.5%～94.1%.The epitope analysis of the isolate showed that no mutation was found in the 15 highly conserved cysteine sites of the E2 protein.Some mutations were observed in GD02 such as K31R,N34S,N88S,S90A,S108T,K159R,N174K,meanwhile GD19 was observed mutations such as N88S,S90V,S108T,N174K.However,the effects of these substitutions on viral virulence and immune effects require further investigation.C strain attenuated vaccine and the E2 subunit vaccine are main choice of CSF immunization in China.While using C strain attenuated vaccine,it is hard to distinguish immunized pigs from virus challenged pigs though the vaccine can provide enough protection to immunized pigs.Therefore,comparation of protection from CSF between C-strain vaccine and E2 subunit vaccine was made in this study,30 pigs aged 5 months were divided into 6 groups and each group maintained 5 pigs.All pigs except positive and negative groups were immunized.At 35 dpi,1 m L of 10⁵ TCID₅₀ virus（strain name:GD19,2.1 g subtype）was inoculated for challenge to each pig except the negative group.Body temperature changes were measured every day since 0 dpi.Blood samples were collected to measure E2,E0,NS antibodies and white blood cell levels by means of ELISA.Oropharyngeal swabs and blood samples were collected to measure virus titer by means of q PCR.All pigs were euthanized and subjected to case necropsy and pathological sectioning of organs at 21 dpc.CSFV could be only detected in pigs of positive group.The results of necropsy and pathological section showed that the degree of organ lesions in the E2 subunit vaccine group was less than that of the C strain attenuated vaccine group after challenge.Above all,this study shows that both E2 subunit vaccine and C strain attenuated vaccine can protect immunized pigs from CSFV challenged.