African Swine Fever Virus Georgia 2007 With A Deletion Of Virulence-Associated Gene 9gl (B119l), When Administered At Low Doses, Leads To Virus Attenuation In Swine And Induces An Effective Protection Against Homologous Challenge

African swine fever virus (ASFV) is the etiological agent of an often lethal disease of domestic pigs. Disease control strategies have been hampered by the unavailability of vaccines against ASFV. Since its introduction in the Republic of Georgia, a highly virulent virus, ASFV Georgia 2007 (ASFV-G), has caused an epizootic that spread rapidly into Eastern European countries. Currently no vaccines are available or under development to control ASFV-G. In the past, genetically modified ASFVs harboring deletions of virulence-associated genes have proven attenuated in swine, inducing protective immunity against challenge with homologous parental viruses. Deletion of the gene 9GL (open reading frame [ORF] B119L) in highly virulent ASFV Malawi-Lil-20/1 produced an attenuated phenotype even when administered to pigs at 10(6) 50% hemadsorption doses (HAD(50)). Here we report the construction of a genetically modified ASFV-G strain (ASFV-G-Delta 9GLv) harboring a deletion of the 9GL (B119L) gene. Like Malawi-Lil-20/1-Delta 9GL, ASFV-G-Delta 9GL showed limited replication in primary swine macrophages. However, intramuscular inoculation of swine with 10(4) HAD(50) of ASFV-G-Delta 9GL produced a virulent phenotype that, unlike Malawi-Lil-20/1-Delta 9GL, induced a lethal disease in swine like parental ASFV-G. Interestingly, lower doses (10(2) to 10(3) HAD(50)) of ASFV-G-Delta 9GL did not induce a virulent phenotype in swine and when challenged protected pigs against disease. A dose of 10(2) HAD(50) of ASFV-G-Delta 9GLv conferred partial protection when pigs were challenged at either 21 or 28 days postinfection (dpi). An ASFV-G-Delta 9GL HAD(50) of 10(3) conferred partial and complete protection at 21 and 28 dpi, respectively. The information provided here adds to our recent report on the first attempts toward experimental vaccines against ASFV-G.IMPORTANCEThe main problem for controlling ASF is the lack of vaccines. Studies on ASFV virulence lead to the production of genetically modified attenuated viruses that induce protection in pigs but only against homologous virus challenges. Here we produced a recombinant ASFV lacking virulence-associated gene 9GL in an attempt to produce a vaccine against virulent ASFV-G, a highly virulent virus isolate detected in the Caucasus region in 2007 and now spreading though the Caucasus region and Eastern Europe. Deletion of 9GL, unlike with other ASFV isolates, did not attenuate completely ASFV-G. However, when delivered once at low dosages, recombinant ASFV-G-Delta 9GL induces protection in swine against parental ASFV-G. The protection against ASFV-G is highly effective after 28 days postvaccination, whereas at 21 days postvaccination, animals survived the lethal challenge but showed signs of ASF. Here we report the design and development of an experimental vaccine that induces protection against virulent ASFV-G.