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.

Inoculation with ASFV-Katanga-350 Partially Protects Pigs from Death during Subsequent Infection with Heterologous Type ASFV-Stavropol 01/08.

African swine fever virus (ASFV) is an extremely genetically and phenotypically heterogeneous pathogen. Previously, we have demonstrated that experimental inoculation of pigs with an attenuated strain, Katanga-350 (genotype I, seroimmunotype I) (ASFV-Katanga-350), can induce protective immunity in 80% of European domestic pigs against the homologous virulent European strain Lisbon-57. At least 50% of the surviving pigs received protection from subsequent intramuscular infection with a heterologous virulent strain, Stavropol 01/08 (genotype II, seroimmunotype VIII) (ASFV-Stavropol 01/08). In this study, we assessed clinical signs, the levels of viremia, viral DNA, anti-ASFV antibodies and post-mortem changes caused by subsequent intramuscular injection with ASFV-Katanga-350 and heterologous ASFV-Stavropol 01/08. Inoculation of pigs with the ASFV-Katanga-350 did not protect animals from the disease in the case of the subsequent challenged ASFV-Stavropol 01/08. However, 40% of pigs were protected from death. Moreover, the surviving animals showed no pathomorphological changes or the presence of an infectious virus in the organs after euthanasia at 35 days post challenging. The ability/inability of attenuated strains to form a certain level of protection against heterologous isolates needs a theoretical background and experimental confirmation.

Immunobiological Characteristics of the Attenuated African Swine Fever Virus Strain Katanga-350.

The African swine fever virus (ASFV) is the cause of a recent pandemic that is threatening the global pig industry. The virus infects domestic and wild pigs and manifests with a variety of clinical symptoms, depending on the strain. No commercial vaccine is currently available to protect animals from this virus, but some attenuated and recombinant live vaccine candidates might be effective against the disease. This article describes the immunobiological characteristics of one such candidate-the laboratory-attenuated ASFV strain, Katanga-350-which belongs to genotype I. In this study, we assessed clinical signs and post-mortem changes, the levels of viremia and the presence of viral DNA caused by injection of ASF virus strains Katanga-350, Lisbon-57, and Stavropol 08/01. Intramuscular injection of this strain protected 80% of pigs from a virulent strain of the same genotype and seroimmunotype (Lisbon-57). At least 50% of the surviving pigs received protection from subsequent intramuscular infection with a heterologous (genotype II, seroimmunotype VIII) virulent strain (Stavropol 08/01). Virus-specific antibodies were detectable in serum and saliva samples between 8-78 days after the first inoculation of the Katanga-350 strain (the observational period). The results suggested that this strain could serve as a basis for the development of a recombinant vaccine against ASF viruses belonging to seroimmunotype I.

An Assessment of Diagnostic Assays and Sample Types in the Detection of an Attenuated Genotype 5 African Swine Fever Virus in European Pigs over a 3-Month Period.

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.

Virulent strain of African swine fever virus eclipses its attenuated derivative after challenge.

African swine fever (ASF) is one of the most devastating diseases affecting the swine industry worldwide. No effective vaccine is currently available for disease prevention and control. Although live attenuated vaccines (LAV) have demonstrated great potential for immunizing against homologous strains of African swine fever virus (ASFV), adverse reactions from LAV remain a concern. Here, by using a homologous ASFV Congo strain system, we show passage-attenuated Congo LAV to induce an efficient protective immune response against challenge with the virulent parental Congo strain. Notably, only the parental challenge Congo strain was identified in blood and organs of recovered pigs through B602L gene PCR, long-range PCR, nucleotide sequencing and virus isolation. Thus, despite the great protective potential of homologous attenuated ASFV strain, the challenge Congo strain can persist for weeks in recovered pigs and a recrudescence of virulent virus at late time post-challenge may occur.