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

Abstract

African swine fever virus (ASFV) is 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-⌬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.A frican swine fever (ASF) is a contagious viral disease of swine. The causative agent, ASF virus (ASFV), is a large enveloped virus containing a double-stranded DNA (dsDNA) genome of approximately 190 kbp. ASFV shares aspects of genome structure and replication strategy with other large dsDNA viruses, including the Poxviridae, Iridoviridae, and Phycodnaviridae (1). ASF causes a spectrum of disease that ranges from highly lethal to subclinical, depending on host characteristics and the virulence of circulating virus strains (2). ASFV infections in domestic pigs are often fatal and are characterized by high fever, hemorrhages, ataxia, and severe depression.Currently, the disease is endemic in more than 20 sub-Saharan African countries. In Europe, ASF is endemic on the island of Sardinia (Italy), and outbreaks of ASF have been recorded in the Caucasus region since 2007, affecting Georgia, Armenia, Azerbaijan, and Russia. Isolated outbreaks have been recently reported in Ukraine, Belarus, Lithuania, Latvia, and Poland, posing the risk of further dissemination into neighboring countries. The epidemic

Simultaneous Deletion of the 9GL and UK Genes from the African Swine Fever Virus Georgia 2007 Isolate Offers Increased Safety and Protection against Homologous Challenge

“…ASFV-G-Δ9GL/ΔUK was completely attenuated even at doses 100 times higher than those at which ASFV-G-Δ9GL became virulent (10 4 HAD 50 ) (13).…”

“…Several attenuated strains, obtained by genetic manipulation consisting of single-gene deletions, have been shown to induce protection against the virulent parental virus (10-13, 15, 17). In some cases, a single-gene deletion did not completely attenuate the virus, particularly when it was attempted to increase immunogenicity by using larger quantities of virus (13). We hypothesized that combined deletion of virulence-associated genes would modulate the resulting recombinant virus.…”

“…with any of the prescribed doses of ASFV-G-Δ9GL/Δ9UK did not present with any ASF-related signs, remaining clinically normal during the entire observation period (21 days). Therefore, deletion of the 9GL and UK genes produced complete attenuation of the parental virulent ASFV-G. Deletion of the UK gene enhanced attenuation of ASFV-G-Δ9GL to the extent that 10 6 HAD 50 of ASFV-G-Δ9GL/ΔUK was completely attenuated, while animals inoculated with 10 4 HAD 50 of ASFV-G-Δ9GL presented various levels of disease (13).…”

“…1A) was deleted from ASFV-G and replaced with a cassette containing the p72GUS reporter gene cassette (see Materials and Methods). The recombinant virus was obtained after 11 successive plaque purification events on monolayers of primary swine macrophage cultures (13). The second recombination event replaced the UK gene with a cassette containing the fluorescent mCherry gene under the ASFV p72 promoter.…”

Increasing importance of genomics in recognition of infectious animal diseases taking into account OIE requirements

“…Zastosowana metoda pozwoliła na potwierdzenie wprowadzonych w obrębie genomu ASFV punktowych zmian genetycznych, które warunkowały utracenie przez ten wirus właściwości patogennych dla eksperymentalnie zakażonych świń (28).…”