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.

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.

Understanding the immunological mechanisms of protection and the viral proteins involved in the induction of a protective immune response to the African swine fever virus (ASFV) is still limited. In the last years, the CD2v protein (gp110-140) of the ASFV has been proven to be a serotype-specific protein. Current work is devoted to the investigation of the possibility of creating protection against virulent ASFV strain Mozambique-78 (seroimmunotype III) in pigs previously vaccinated with vaccine strain FK-32/135 (seroimmunotype IV) and then immunized with the pUBB76A_CD2v plasmid, containing a chimeric nucleotide sequence from the CD2v protein gene (EP402R, nucleotides from 49 to 651) from the MK-200 strain (seroimmunotype III). Vaccination with the ASFV vaccine strain FK-32/135 protects pigs from the disease caused by the strain with homologous seroimmunotype—France-32 (seroimmunotype IV). Our attempt to create balanced protection against virulent strain Mozambique-78 (seroimmunotype III) by induction of both humoral factors of immunity (by vaccination with strain FK-32/135 of seroimmunotype IV) and serotype-specific cellular immunity (by immunization with the plasmid pUBB76A_CD2v of seroimmunotype III) was unsuccessful.

The extreme genetic and immunobiological heterogeneity exhibited by the African swine fever virus (ASFV) has been a significant impediment in the development of an efficacious vaccine against this disease. Consequently, the lack of internationally accepted protocols for the laboratory evaluation of candidate vaccines has become a major concern within the scientific community. The formulation of such protocols necessitates the establishment of a consensus at the international level on methods for the determination of homologous and heterologous isolates/strains of ASFV. The present article provides a comprehensive description of biological techniques employed in the classification of ASFV by seroimmunotypes. These techniques involve a holistic evaluation of ASFV isolates/strains based on their antigenic properties as determined by the hemadsorption inhibiting test (HAdI) using type-specific sera and an immunological test (IT) conducted on pigs inoculated with attenuated strains. The article outlines the methods for setting up the HAdI test, an IT on pigs, and the processes involved in the acquisition of type-specific serums for the HAdI test. It is pertinent to note that the definitive classification of seroimmunotype can only be ascertained after conducting an IT on pigs. The findings from the HAdI test or the phylogenetic analysis of the EP402R gene should be considered preliminary in nature.

African swine fever virus causes hemorrhagic disease in swine. Attenuated strains are reported in Africa, Europe, and Asia. Few studies on the diagnostic detection of attenuated ASF viruses are available. Two groups of pigs were inoculated with an attenuated ASFV. Group 2 was also vaccinated with an attenuated porcine reproductive and respiratory syndrome virus vaccine. Commercially available ELISA, as well as extraction and qPCR assays, were used to detect antibodies in serum and oral fluids (OF) and nucleic acid in buccal swabs, tonsillar scrapings, OF, and blood samples collected over 93 days, respectively. After 12 dpi, serum (88.9% to 90.9%) in Group 1 was significantly better for antibody detection than OF (0.7% to 68.4%). Group 1′s overall qPCR detection was highest in blood (48.7%) and OF (44.2%), with the highest detection in blood (85.2%) from 8 to 21 days post inoculation (dpi) and in OF (83.3%) from 1 to 7 dpi. Group 2′s results were not significantly different from Group 1, but detection rates were lower overall. Early detection of attenuated ASFV variants requires active surveillance in apparently healthy animals and is only reliable at the herd level. Likewise, antibody testing will be needed to prove freedom from disease.

African swine fever (ASF) is a lethal hemorrhagic disease of Suidae, i.e., domestic pigs and wild boars, caused by African swine fever virus (ASFV). The development of cross-protective vaccines against ASF is imperative for effective disease control, particularly in regions where ASF is endemic, potentially featuring multiple circulating ASFV isolates. The investigation of non-hemadsorbing naturally attenuated isolates and laboratory recombinant strains with a deletion in the EP402R gene has attracted interest. Our study aimed to assess the impacts of various administration routes and doses of the naturally attenuated ASFV-PSA-1NH (immunotype IV, genotype I) isolate on the manifestation of clinical signs of ASF and the level of protection against the heterologous ASFV-Stavropol 01/08 strain (seroimmunotype VIII, genotype II). The results demonstrated that the intranasal administration of a low dose of ASFV-PSA-1NH to pigs minimized the clinical signs of ASF and established a high level of protection against the heterologous strain ASFV-Stavropol 01/08. Despite the challenges in standardizing the dosage for intranasal administration, this approach appears as a viable alternative in ASF vaccination.