African swine fever virus (ASFV) causes high morbidity and mortality in swine (Sus scrofa), for which there is no commercially available vaccine. Recent outbreaks of the virus in Trans-Caucasus countries, Eastern Europe, Belgium and China highlight the urgent need to develop effective vaccines against ASFV. Previously, we evaluated the immunogenicity of a vaccination strategy designed to test various combinations of ASFV antigens encoded by DNA plasmids and recombinant proteins with the aim to activate both humoral and cellular immunity. Based on our previous results, the objective of this study was to test the combined DNA-protein vaccine strategy using a cocktail of the most immunogenic antigens against virulent ASFV challenge. Pigs were vaccinated three times with a cocktail that included ASFV plasmid DNA (CD2v, p72, p32, +/−p17) and recombinant proteins (p15, p35, p54, +/−p17). Three weeks after the third immunization, all pigs were challenged with the virulent ASFV Armenia 2007 strain. The results showed that vaccinated pigs were not protected from ASFV infection or disease. Compared to the non-vaccinated controls, earlier onset of clinical signs, viremia, and death were observed for the vaccinated animals following virulent ASFV challenge. ASFV induced pathology was also enhanced in the vaccinated pigs. Furthermore, while the vaccinated pigs developed antigen-specific antibodies, immunized pig sera at the time of challenge lacked the capacity to neutralize virus, and instead was observed to enhance ASFV infection in vitro. The results of this work points to a putative immune enhancement mechanism involved in ASFV pathogenesis that warrants further investigation. This pilot study provides insight for the selection of appropriate combinations of ASFV antigens for the development of a rationally-designed, safe, and efficacious vaccine for ASF.

Influenza viruses are important pathogens causing respiratory disease in humans and animals. In contrast to influenza A virus (IAV) that can infect a wide range of animal species, other influenza viruses, including influenza B virus (IBV), influenza C virus (ICV), and influenza D virus (IDV) have a limited host range. Swine can be infected with all four different genera of influenza viruses. IAV infection of pigs causes the well-known swine influenza that poses significant threats to human and animal health. However, influenza virus infection of pigs with IBV, ICV, and IDV are not well-characterized. Herein, we compared pathogenicity of IBV and IDV using intratracheal and intranasal infection of pigs, which are IAV seropositive, and commingled naïve pigs with the infected animals to determine their transmissibility. Both viruses caused fever and some lung lesions, replicated in the lungs of infected pigs, but only IDV transmitted to the contact animals. Although IBV and IDV displayed differing levels of replication in the respiratory tract of infected pigs, no significant differences in pathogenicity of both viruses were observed. These results indicate that both IBV and IDV can replicate, and are pathogenic in pigs.

African swine fever (ASF) is an obligated declaration swine disease, provoking farm isolation measures and the closing of affected country boarders. ASF virus (ASFV) is currently the cause of a pandemic across China and Eurasia. By the end of 2019, ASF was detected in nine EU Member States: Bulgaria, Romania, Slovakia, Estonia, Hungary, Latvia, Lithuania, Poland and Belgium. The affected area of the EU extended progressively, moving mostly in a southwestern direction (EFSA). Inactivated and/or subunit vaccines have proven to fail since certain virus replication is needed for protection. LAVs are thus the most realistic option, which must be safe, effective and industrially scalable. We here generated a vaccine prototype from the Arm/07/CBM/c2 genotype II strain, in which we have deleted the EP402R (CD2v) and A238L genes by CRISPR/Cas9 in COS-1 cells, without detectable further genetic changes. The successful immunization of pigs has proven this vaccine to be safe and fully protective against the circulating Korean Paju genotype II strain, opening the possibility of a new vaccine on the market in the near future.

African swine fever virus (ASFV) is the etiological agent causing African swine fever (ASF), affecting domestic pigs and wild boar, which is currently the biggest animal epidemic in the world and a major threat to the swine sector. At present, some safety concerns about using LAVs against ASFV still exist despite a commercial vaccine licensed in Vietnam. Therefore, the efforts to identify virulence factors and their mechanisms, as well as to generate new vaccine prototypes, are of major interest. In this work, we have identified the MGF505-2R gene product as an inhibitor of the cGAS/STING pathway, specifically through its interaction with STING protein, controlling IFN-β production. In addition, immunization of a recombinant virus lacking this gene, Arm/07-ΔMGF505-2R, resulted in complete attenuation, demonstrating its involvement in ASFV virulence. Finally, immunization with Arm/07-ΔMGF505-2R induced the generation of antibodies and proved to be partially protective against virulent ASFV strains. These results identify MGF505-2R, as well as its mechanism of action, as a gene contributing to understanding the molecular mechanisms of ASFV virulence, which will be of great value in the design of future vaccine prototypes.

The antigenically conserved hemagglutinin stalk region is a target for universal influenza virus vaccines since antibodies against it can provide broad protection against influenza viruses of different subtypes. We tested a universal influenza virus vaccination regimen based on sequential immunization with chimeric hemagglutinin (HA) containing viruses in a swine influenza virus pig model with maternal antibodies against pandemic H1N1. Vaccines were administered as live attenuated virus or inactivated influenza virus split vaccine (+/− Emulsigen adjuvant). As controls, we included groups that received trivalent inactivated influenza vaccine that contained pandemic H1N1 antigens, inactivated adjuvanted H1N2 vaccine (control group for vaccine associated enhanced respiratory disease in the pig model) or mock-vaccination. No induction of H1 head or stalk-specific antibody responses was observed upon vaccination, while responses against H3 and influenza B HA were elicited in the group vaccinated with the trivalent vaccine. Four weeks post vaccination, pigs were intratracheally challenged with pandemic H1N1 virus and euthanized 5 days after challenge. Despite the lack of detectable anti-stalk immunity, the chimeric hemagglutinin vaccine resulted in better clinical outcomes compared to control groups.