This article summarizes the study results on the generation of attenuated strains of African swine fever virus (ASFV) of seroimmunotypes I–VIII and the creation of live vaccines for temporary protection of pigs during a period of epizootics in the surveillance zone (a zone adjacent to the area of outbreak). These studies were initiated at the Federal Research Center for Virology and Microbiology (FRCVM, formerly VNIIVViM) at the time of introduction of the pathogen to the Iberian Peninsula in the middle of the 20th century. The developed experimental vaccines against ASFV seroimmunotypes I–V provided protection against virulent strains of homologous seroimmunotypes by day 14 after vaccination, lasting at least four months.

This article is devoted to the development and evaluation of the immunoblotting test system for serological diagnosis of African swine fever (ASF), based on the highly purified recombinant p30 of ASF virus (ASFV) strain Stavropol 01/08 (Stavropol 2008), representative of the ASFV currently circulating in the Russian Federation. The main project stages are as follows: (i) cloning of the central hydrophilic region of the ASFV gene CP204L (p30) into a prokaryotic vector; (ii) expression and chromatographic purification of the recombinant product p30 with thioredoxin and poly-histidine site (p30e1_TrxA_6xHis); (iii) development of the immunoblotting test system (Rec p30-IB) using the highly purified recombinant p30; and (iv) evaluation of Rec p30-IB using sera and organ samples from domestic pigs and wild boars experimentally or naturally infected by ASFV. Testing of the Rec p30-IB showed the diagnostic specificity and sensitivity of the assay to be 98.75% and 100.00%, respectively. High sensitivity of the Rec p30-IB allowed the detection of ASFV-specific antibodies in samples of organs of the immune system and blood sera, collected from domestic pigs and wild boars, starting from 6 to 8 days post-infection, regardless of virus virulence, seroimmunotype and geographic origin of the samples (East Europe, South Europe, West Europe, Central and south-east Africa).

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This review presents comparative results of simultaneously conducted studies on proteins responsible for the haemadsorption and serotype-specific properties of African swine fever virus (ASFV). An ASFV gene EP402R (or LMW8-DR) encoding protein CD2v homologous to murine, human or porcine T-cell adhesive receptor was found. The CD2v was shown to be directly involved into a haemadsorption process, and expressed in ASFV-infected cells as a glycoprotein with a molecular weight of approximately 105-110 kDa. In the presence of a glycosylation inhibitor, tunicamycin, its molecular weight is about 42 kDa. In ASFV-infected cells labeled with 3 H-glucosamine or 14 C-sodium acetate, a virus-specific major glycoprotein with a molecular weight of 110-140 kDa (gp 110-140) was identified using radioimmunoprecipitation assay. Using ASFV reference strains belonging to seroimmunotypes I-IV and the corresponding antisera active in haemadsorption inhibition assay (HADIA), we determined that gp 110-140 defines the serotype specificity. Genotyping on the basis of the genetic locus encoding the CD2v and a C-type lectin protein also showed a concurrence with the grouping of ASFV isolates and strains based on their seroimmunotypes. Immunization of pigs with the gp 110-140 within liposomes, or a recombinant haemagglutinin (CD2v) protected 67 to 100% of animals from death due to their subsequent infection with homologous virulent ASFV strains. Based on the physico-chemical and biological characteristics of the gp 110-140 and CD2v it is suggested that they are one and the same virus-specific glycoprotein crucial for induction of the immunological protection against ASF.

African swine fever (ASF) is an infectious disease of domestic and wild pigs of all breeds and ages, with the acute form of the disease being characterized by high fever, hemorrhages in the reticuloendothelial system and a high mortality rate. Registered safe and efficacious ASF vaccines are not available. The development of experimental ASF vaccines, particularly live attenuated, have considerably intensified in the last years. There is much variability in experimental approaches undertaken by laboratories attempting to develop first generation vaccines, rendering it difficult to interpret and make comparisons across trials. ASF virus (ASFV) genotyping does not fully correlate with available cross-protection data and may be of limited value in predicting cross-protective vaccine efficacy. Recently, ASFV strains were assigned to a respective nine groups by seroimmunotype (from I to IX): in vivo the grouping is based on results of cross protection of pigs survived after their infection with a virulent strain (bioassay), while in vitro this grouping is based on hemadsorption inhibition assay (HADIA) data. Here we demonstrate the antigenic and protective properties of two attenuated ASFV strains MK200 and FK-32/135. Pronounced differences in the HADIA and in immunological test in animals allow us to consider them and the corresponding reference virulent strains of the ASFV of Mozambique-78 (seroimmunotype III, genotype V) and France-32 (seroimmunotype IV, genotype I) as useful models for studying the mechanisms of protective immunity and evaluation of the candidate vaccines.