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Abstract
African swine fever (ASF) is a contagious, hemorrhagic and highly lethal viral disease in swine. Following the initial report of ASF in Kenya in 1921 it spread to East Asia through Western Europe and Russia (including Eastern Europe). Many efforts have been dedicated to controlling ASF but the struggle to eradicate this disease continues. Thus far, the efforts to develop an effective vaccine to control ASF have been unsuccessful. A previous inactivated ASF vaccine, developed by traditional methods, failed to protect pigs from ASF virus (ASFV) infection. Neutralizing antibodies were not effective in inducing protective immunity and it appears that cellular immunity is required. To develop an effective ASF vaccine the identification of protective antigens of ASFV has been explored and subunit vaccines that target these potential protective antigens have induced partial protection. DNA vaccines that induce cellular immunity have been effective in inducing protection against ASFV infection. ASFV live attenuated vaccines (LAVs) can be rationally designed and engineered via comparative and functional genomics. LAVs have a major safety concern despite their high protective efficacy. ASF vaccines are urgently needed to control ASF; however, many obstacles remain to be overcome to develop an effective ASF vaccine.
Keywords: African swine fever (ASF), ASF vaccine, Subunit vaccine, Cellular immunity, Live attenuated vaccines _(LAVs)_
Introduction
African swine fever (ASF) is a contagious and hemorrhagic viral disease affecting swine that threatens the swine industry worldwide (Costard et al., 2013; Dixon et al., 2019a). The causative agent of ASF is the ASF virus (ASFV; the sole member of Asfarviridae), a large enveloped, double-stranded DNA virus (Alonso et al., 2018). ASF occurs in several forms, ranging from the highly lethal (up to 100% mortality) to subclinical. The symptoms of the severe form in pigs infected with highly virulent ASFV strains include hemorrhages, edema, ascites, and shock, resulting from leaking blood vessels (Villeda et al., 1993; GomezVillamandos et al., 1995). Warthogs (Phacochoerus aethiopicus), bushpigs (Potamochoerus porcus), and giant forest hogs (Hylochoerus meinertzhageni) are natural hosts of ASFV; they do not show symptoms even when infected, transmit ASFV easily, and they are considered a reservoir of ASFV (Blome et al., 2013). Soft ticks belonging to Ornithodoros, also act as vectors of ASFV (Pereira de Oliveira et al., 2019).
ASF was first...