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Title: Progressive adaptation of a Georgian isolate of African swine fever virus to vero cells leads to a gradual attenuation of virulence in swine corresponding to major changes of the viral genome

Author
item Krug, Peter
item Holinka-Patterson, Lauren
item O'DONNELL, VIVIAN - University Of Connecticut
item REESE, BO - University Of Connecticut
item Sanford, Brenton
item FERNANDEZ-SAINZ, IGNACIO - University Of Connecticut
item GLADUE, DOUGLAS - University Of Connecticut
item Arzt, Jonathan
item Rodriguez, Luis
item RISATTI, GUILLERMO - University Of Connecticut
item Borca, Manuel

Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2014
Publication Date: 12/10/2014
Publication URL: http://handle.nal.usda.gov/10113/61571
Citation: Krug, P.W., Holinka-Patterson, L.G., O'Donnell, V., Reese, B., Sanford, B.J., Fernandez-Sainz, I., Gladue, D.P., Arzt, J., Rodriguez, L.L., Risatti, G.R., Borca, M.V. 2014. Progressive adaptation of a Georgian isolate of African swine fever virus to vero cells leads to a gradual attenuation of virulence in swine corresponding to major changes of the viral genome. Journal of Virology. 89(4):2324-2332.

Interpretive Summary: African swine fever virus (ASFV) causes a contagious and often lethal disease of feral and domestic swine. No vaccines are currently available to control the disease. Some experimental vaccines have been developed by adapting the virus to grow in specific cell cultures. This process of adaptation usually produces a weakening of the virus. We report here the characterization of a virus strain isolated in the Republic of Georgia, called ASFV-G, that has been adapted to grow in a common cell line (Vero cells) used in research. We demonstrated that after 110 generations the virus became unable to produce disease in pigs. Also, the adaptation to grow in Vero cells is associated with a progressive loss of the virus’ ability to grow in swine stationary tissue cells. In addition, the analysis of the genetic material of the virus demonstrates particular genes may be related to the changes in the virulence of the virus.

Technical Abstract: African swine fever virus (ASFV) causes a contagious and often lethal disease of feral and domestic swine. Experimental vaccines derived from naturally occurring, genetically modified or cell culture-adapted ASFV have been evaluated but no commercial vaccine is available to control African Swine Fever (ASF). We report here the characterization of a virus strain derived from the ASFV isolate in the Republic of Georgia (ASFV-G) isolate that has been adapted to grow in the Vero cell line. ASFV-G virus was successively passaged 110 times in Vero cells and its ability to replicate in Vero cells and primary swine macrophages as well as its virulence in swine, was assessed at passages 30, 60, 80 and 110 along with genomic modifications observed at each of the indicated passages. Replication of ASFV-G increased with successive passaging in Vero cells, while a corresponding decreased replicative ability was observed in primary swine macrophages. These observations were also confirmed in vivo; a progressive and significant loss in its ability to produce disease in swine occurred, with complete attenuation of the virus by passage 110. Nevertheless, infection with attenuated virus did not confer protection against challenge with the virulent parental virus. Comparison of the full-length sequence of each of the analyzed passages identified two significant deleted areas along with minor additional amino acid substitutions and frame shift mutations in selected open reading frames. The possible importance of these genetic changes in virus adaptation/attenuation is discussed.