Serological behaviour of isolated African swine fever virus. Brief report

Administration Routes and Doses of the Attenuated African Swine Fever Virus Strain PSA-1NH Influence Cross-Protection of Pigs against Heterologous Challenge

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.

Seroimmunotyping of African swine fever virus

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.

The attenuated ASFV strains MK-200 and FK-32/135 as possible models for investigation of protective immunity by ASFV infection

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.

A systematic review of genotypes and serogroups of African swine fever virus

African swine fever virus (ASFV) is the causative agent of African swine fever (ASF). The virus causes an acute highly hemorrhagic disease in domestic pigs, with high mortality. Although the overall genome mutation rate of ASFV, a large DNA virus, is relatively low, ASFV exhibits genetic and antigenic diversity. ASFV can be classified into 24 genotypes on the basis of the B646L gene. Cross-protected ASFV strains can be divided into eight serogroups on the basis of antibody-mediated hemadsorption inhibition. Here, we review research progress on ASFV genotyping and serogrouping, and explain how this information assists in the rapid identification of virus origin during ASF outbreaks and will aid in the development of ASF vaccines.

Thoughts on African Swine Fever Vaccines

African swine fever (ASF) is an acute viral hemorrhagic disease of domestic swine with mortality rates approaching 100%. Devastating ASF outbreaks and continuing epidemics starting in the Caucasus region and now in the Russian Federation, Europe, China, and other parts of Southeast Asia (2007 to date) highlight its significance. ASF strain Georgia-07 and its derivatives are now endemic in extensive regions of Europe and Asia and are "out of Africa" forever, a situation that poses a grave if not an existential threat to the swine industry worldwide. While our current concern is Georgia-07, other emerging ASFV strains will threaten for the indefinite future. Economic analysis indicates that an ASF outbreak in the U.S. would result in approximately $15 billion USD in losses, assuming the disease is rapidly controlled and the U.S. is able to reenter export markets within two years. ASF's potential to spread and become endemic in new regions, its rapid and efficient transmission among pigs, and the relative stability of the causative agent ASF virus (ASFV) in the environment all provide significant challenges for disease control. Effective and robust methods, including vaccines for ASF response and recovery, are needed immediately.

Rapid Identification for Serotyping of African Swine Fever Virus Based on the Short Fragment of the EP402R Gene Encoding for CD2-Like Protein

The first confirmed case of African swine fever (ASF) in Vietnam was officially reported in February 2019. To date, the ASF virus (ASFV) has been detected in all 63 cities/provinces in Vietnam. In order to get a better understanding of the potential role of the EP402R gene in a grouping of ASFV serotypes, thirty ASFV sequences of EP402R genes (accession numbers: MN711757-86) from North Central Coast of Vietnam and 68 well-known references of serotype groups from previous studies were further analyzed. Interestingly, we found that a short fragment of 90 nucleotides was very typical for 8 serological groups of ASFVs. A primer set was designed to amplicon the short fragment of 90 nucleotides using the Primer3 program to establish a simplified method for the serotyping of ASFV. Our results indicated that phylogenetic analysis of the short fragment (90 nucleotides) of the EP402R gene is a very specific and useful method for ASFV serotyping when compared to the previous method using a long fragment (816 nucleotides) of this gene and well-known serotype references based on haemadsorption inhibition (HAI) assay.

Clinical and Pathological Study of the First Outbreak Cases of African Swine Fever in Vietnam, 2019

African swine fever (ASF) is a devastating disease of swine and the most important disease for the pork industry. Since the outbreaks in 2007 in the Caucasian region, it has been spreading to the West and East quite swiftly. In this study we have analyzed the clinical signs and pathological features of the first outbreaks on ASF in Vietnam in 2019, caused by an isolate with 100% similarity to the genotype II (p72) isolates from Georgia in 2007 and China in 2018. The disease onset with a peracute to acute clinical course with high mortality. Some animals showed very unspecific clinical signs with other showing severe hyperthermia, respiratory distress, diarrhea, or vomit. Hemorrhagic splenomegaly and lymphadenitis were the main lesions observed at post mortem examination, with histopathological changes confirming the lymphoid depletion and multiorganic hemorrhages. Monocyte-macrophages were identified by means of immunohistochemical methods as the main target cell for the ASF virus in tissue sections.

Challenges for African swine fever vaccine development-"… perhaps the end of the beginning."

African swine fever (ASF), an acute, viral hemorrhagic disease in domestic swine with mortality rates approaching 100%, is arguably the most significant emerging disease threat for the swine industry worldwide. Devastating ASF outbreaks and continuing epidemic in the Caucasus region and Russia (2007-to date) highlight significance of this disease threat. There is no vaccine for ASF, thus leaving animal slaughter the only effective disease control option. It is clear, however, that vaccination is possible since protection against reinfection with the homologous strain of African swine fever virus (ASFV) has been clearly demonstrated. Vaccine development has been hindered by large gaps in knowledge concerning ASFV infection and immunity, the extent of ASFV strain variation in nature and the identification of viral proteins (protective antigens) responsible for inducing protective immune responses in the pig. This review focuses on the challenges surrounding ASF vaccine design and development, with an emphasis on existing knowledge gaps.

African swine fever virus serotype-specific proteins are significant protective antigens for African swine fever

African swine fever (ASF) is an emerging disease threat for the swine industry worldwide. No ASF vaccine is available and progress is hindered by lack of knowledge concerning the extent of ASFV strain diversity and the viral antigens conferring type-specific protective immunity in pigs. Available data from vaccination/challenge experiments in pigs indicate that ASF protective immunity may be haemadsorption inhibition (HAI) serotype-specific. Recently, we have shown that two ASFV proteins, CD2v (EP402R) and C-type lectin (EP153R), are necessary and sufficient for mediating HAI serological specificity (Malogolovkin et al., 2015).. Here, using ASFV inter-serotypic chimeric viruses and vaccination/challenge experiments in pigs, we demonstrate that serotype-specific CD2v and/or C-type lectin proteins are important for protection against homologous ASFV infection. Thus, these viral proteins represent significant protective antigens for ASFV that should be targeted in future vaccine design and development. Additionally, these data support the concept of HAI serotype-specific protective immunity.

African swine fever virus CD2v and C-type lectin gene loci mediate serological specificity

African swine fever (ASF) is an emerging disease threat for the swine industry worldwide. No ASF vaccine is available and progress is hindered by lack of knowledge concerning the extent of ASF virus (ASFV) strain diversity and the viral antigens responsible for protection in the pig. Available data from vaccination/challenge experiments in pigs indicate ASF protective immunity is haemadsorption inhibition (HAI) serotype-specific. A better understanding of ASFV HAI serological groups and their diversity in nature, as well as improved methods to serotype ASFV isolates, is needed. Here, we demonstrated that the genetic locus encoding ASFV CD2v and C-type lectin proteins mediates HAI serological specificity and that CD2v/C-type lectin genotyping provides a simple method to group ASFVs by serotype, thus facilitating study of ASFV strain diversity in nature, and providing information necessary for eventual vaccine design, development and efficacious use.

Variable and constant regions in African swine fever virus DNA

An analysis of the SalI restriction pattern of African swine fever virus DNA showed that the SalI recognition sites did not change after more than 100 virus passages in porcine macrophages. The virus strain BA71V, obtained from the virus isolate BA71 by adaptation to grow in VERO cells, differed from the nonadapted virus in two deletions with a length of 2.5 and 7 kb located close to the DNA ends. A restriction analysis of several virus clones obtained from a naturally infected pig revealed length heterogeneity in both variable regions. A comparison of SalI restriction maps from 23 African swine fever virus field isolates (8 African, 11 European, and 4 American) has shown that the virus genome consists of a central region with a constant length of about 125 kb and two variable regions located close to the DNA ends with a length of 38-47 kb for the left DNA end, and 13-16 kb for the right DNA end. The total length of ASF virus DNA varied between 178 (BA71) and 189 (MOZ64) kb. The 23 African swine fever virus isolates were classified into five groups, according to the arrangement of the SalI sites in the central region. Four groups contained only African isolates, whereas all the European and American isolates belonged to the same group. This distribution of isolates suggests that all non-African virus field isolates have a common origin.

Monoclonal antibodies of African swine fever virus: antigenic differences among field virus isolates and viruses passaged in cell culture

An analysis of the binding properties of a collection of monoclonal antibodies to African swine fever virus particles showed that virus field isolates passaged in porcine macrophages changed antigenically more than a strain of a cell-adapted virus passaged in Vero cells. From seven clones isolated from the spleen of a field-infected pig, we found four clones that had the same antigenic properties, one clone that had large changes in proteins p150 and p27 and small changes in proteins p37 and p14, and two clones that had minor changes in proteins p150 and p27, respectively. An analysis of the binding properties of the monoclonal antibodies to 23 field isolates from Africa, Europe, and America showed that the African isolates differed among themselves more than the European and the American isolates; in this study we found changes in 8 of the 10 virus proteins tested. The most variable proteins in the African isolates were p150, p27, p14, and p12. In contrast to the African isolates, protein p12 from the non-African viruses did not change. The clustering of the field virus isolates in six antigenic homology groups indicated the existence of a complex variety of African swine fever virus serotypes.