African swine fever vaccines: a promising work still in progress

Abstract

African swine fever (ASF), a disease of obligatory declaration to the World Organization for Animal Health (OIE), has contributed to poverty and underdevelopment of affected areas. The presence of ASF has been historically neglected in Africa, contributing to its uncontrolled expansion and favouring its spread to continental Europe on at least three occasions, the last one in 2007 through the Republic of Georgia. Since then, African swine fever virus (ASFV) has spread to neighbouring countries, reaching the European Union in 2014, China in the summer of 2018 and spreading through Southeast Asia becoming a global problem. Lack of available vaccines against ASF makes its control even more difficult, representing today the number one threat for the swine industry worldwide and negatively affecting the global commerce equilibrium. Main body: In this review, we intend to put in perspective the reality of ASF vaccination today, taking into account that investment into ASF vaccine development has been traditionally unattractive, overall since ASF-free areas with large swine industries applied a non-vaccination policy for diseases listed by the OIE. The dramatic situation suffered in Asia and the increasing threat that ASF represents for wealthy countries with large swine industries, has dramatically changed the perspective that both private and public bodies have about ASF vaccinology, although this is controversial. The feasibility of modifying the ASFV genome has led to safe and efficacious experimental recombinant live attenuated viruses (LAVs). The main challenge today will be confirming the safety and efficacy of these technologies in the field, accelerating transfer to the industry for official registration and commercialization. The complexity of ASFV, together with the lack of knowledge about the mechanisms involved in protection and the specific antigens involved in it, requires further investment in research and development. Although far from the efficacy achieved by LAVs, subunit vaccines are the optimal choice for the future. If the world can wait for them or not is a contentious issue. Conclusion: Despite their inherent disadvantages, LAVs will be the first technology to reach the market, while subunit vaccines will need much further research to become a successful commercial reality.

Distinct African Swine Fever Virus Shedding in Wild Boar Infected with Virulent and Attenuated Isolates

“…In addition, a low shedding capacity of LAV candidates, which has also been described for the attenuated ASFV NH/P68 vaccine candidate [ 24 ], may help amplify vaccination coverage, thus reducing the need for the expensive production and large-scale administration of vaccine for wild boar in field conditions. This study demonstrates not only that the attenuated Lv17/WB/Rie1 ASFV isolate may be efficacious and safe as a vaccine candidate for the inoculated and in-contact wild boar, but also that the viral excretion from infected animals is limited and is relatively safe for the environment [ 41 , 42 ]. The current situation in the European Union (EU) and some eastern European countries indicates that the wild boar is the most severely affected host, thus conferring upon it an important role in ASF spread and maintenance [ 35 ].…”

Identification of Promiscuous African Swine Fever Virus T-Cell Determinants Using a Multiple Technical Approach

“…Availability of effective vaccines against ASF would greatly improve the management of the disease as well as eradication actions in the future. Currently, LAVs appear as the most feasible vaccine choice in the immediate future, but subunit vaccines are likely the long-term alternative, especially for ASF-free areas reluctant to implement LAVs in the field [ 9 , 44 , 45 ]. Nonetheless, the little information available regarding the ASFV antigens involved in protection is a major gap for the short-term development of efficient subunit vaccines.…”

“…Since its first declaration in China in 2018, most probably due to the importation of contaminated pork products, ASFV has expanded extremely fast to all neighboring countries, reaching more than 28 countries from Asia and Oceania, causing an economic crisis of gigantic proportions [ 7 , 8 ]. Therefore, developing safe and efficacious vaccines against ASF is a priority for the swine industry worldwide [ 9 ].…”

Current State of Global African Swine Fever Vaccine Development under the Prevalence and Transmission of ASF in China

“…Therefore, it brought on doubts about the relevance of p30, p54, and p72 in immune protection and debates about antibody-mediated neutralization protection. Recently, the ASFV serological determinants determined so far have recently been listed by an expert group, and a summary review has been published [ 91 ]. In 2011, Argilaguet et al vaccinated pigs separately with pCMV-PQ, a plasmid encoding p30 and p54, two immunodominant structural viral antigens, and pCMV-APCH1PQ, a plasmid encoding p30, p54 fused with a single chain variable fragment of an antibody specific for a swine leukocyte antigen II (SLA-II).…”

“…On the whole, with only a few ASFV proteins as antigens, it is difficult to provide effective immune protection even if neutralizing antibodies are emerged [ 95 ]. Although DNA vaccines can induce high levels of specific T cell responses in the host [ 91 , 93 ], they still cannot fully resist the challenge of virulent strains. The ASFV coding genes screened by DNA vaccination may play an established role in dissecting the immune mechanism and participating in the protection of ASFV antigens, but there is still a long way to go to achieve the goal of providing effective immune protection.…”