Submitted to: Virus Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 24, 2013
Publication Date: March 7, 2013
Citation: Newcomer, B.W., Neill, J.D., Marley, M.S., Ridpath, J.F., Givens, M.D. 2013. Mutations induced in the NS5B gene of bovine viral diarrhea virus by antiviral treatment convey resistance to the compound. Virus Research. 174(1-2):95-100 DOI: 10.1016/j.virusres.2013.03.007. Interpretive Summary: Bovine viral diarrhea viruses (BVDV) are ubiquitous pathogens cattle and other ruminants. The virus exists as either cytopathic or noncytopathic biotype where the two are differentiated by growth characteristics in cell culture. The noncytopathic viruses have the ability to establish life-long persistent infections (PI) in cattle when a fetus in the first trimester of pregnancy is infected by BVDV. Following birth, the animal spreads the virus continuously to other susceptible cattle, thus acting as a reservoir for the virus. A synthetic compound, DB772, was identified that showed high levels of antiviral activity against BVDV. When this compound was administered to PI cattle, a dramatic drop in circulating virus was observed but within a few days, viral titers had returned to pretreatment levels. The viruses in the treated animals were then shown to be resistant to further treatment with the compound. The genomic RNAs of viruses isolated from treated animals were sequenced to determine the changes that occurred that conferred resistance. This showed that there mutations in the RNA polymerase of the virus. The apparent mechanism of action of the compound is to bind to the RNA polymerase, preventing replication of the genomic RNA. These changes prevent binding of the compound, thus allowing RNA replication to continue. This study demonstrates how quickly genetic change can occur in BVDV and that any antiviral treatments will probably require 2 or more compounds with different modes of action to be effective in treating BVDV infection.
Technical Abstract: Bovine viral diarrhea virus (BVDV) is a widespread bovine pathogen for which there is no specific therapeutic agent. A previous study using 2-(2-benzimidazolyl)-5-[4-(2-imidazolino)phenyl]furan dihydrochloride (DB772) to treat calves persistently infected with BVDV resulted in a decrease in the viral load of infected calves but treatment resulted in the rapid selection of drug-resistant mutant isolates. In this article we describe three mutations found in the mutant isolates associated with in vivo and in vitro resistance to DB772. All three mutations are found in the NS5B which functions as the RNA-dependent-RNA-polymerase during viral replication. Growth curves for the mutant isolates were not largely different from those of wild-type isolates when cultured in the absence of DB772. Thus, DB772 appears to act by binding to the specified domain but binding is disrupted or inhibited by the described mutation.