Antiviral Research, 1 (1981)47-53 47 Elsevier/North-Holland Biomedical Press BOVINE LEUKEMIA VIRUS INHIBITION IN VITRO BY RIBAVIRIN ROBERT W. SIDWELL 2 and DONALD F. SMEE~ Departments o f 1Biology and 2Animal, Dairy and Veterinary Science, UMC 56, Utah State University, Logan, UT 84322, U.S.A. (Received 12 August 1980; accepted 17 November 1980) Ribavitin treatment of an established monolayer of fetal lamb kidney (FLK) cells chronically infected with bovine leukemia virus (BLV) resulted in inhibition of the extra- and intracellular internal viral polypeptide antigen, as measured by CF test, at concentrations of 10 and 32 ug/ml, respectively. Similar treatment of F-81 cells newly infected with BLV caused significant reduction in viral syncytia formation at ribavirin levels as low as 3.2 /~g/ml. Attempts to eliminate or reduce the BLV infection in FLK cells by 8 passages of the cells in the continual presence of 3.2 or 1.0 ug/ml of ribavirin were unsuccessful. Multiple passages of ELK cells in the presence of higher concentrations of ribavirin substantially retarded cell growth, although short-term treatment of established cell monolayers appeared to be well tolerated as evidenced by cell appearance. Biochemical cytostatic studies of resting F-81 cell monolayers showed cytostatic effects at the same dosage levels where antiviral effects occurred. ribavirin virazole 1-#-D-ribofurasonyl-1,2,4-triazole-3-carboxamide bovine leukemia virus INTRODUCTION The bovine leukemia virus (BLV), an oncogenic retrovirus, is widely distributed in cattle populations and is considered the etiologic agent of bovine lymphosarcoma or leucosis [16]. The disease induced by BLV appears to be increasing in economic impor- tance as awareness of the disease heightens and additional requirements mount for testing for presence of BLV infection prior to export. The virus also has oncogenic potential in experimentally inoculated sheep [8, 15, 17] and goats [5]. Little has yet been accomplished to control BLV infections; a brief report [ 1] has des- cribed the use of an unidentified potential antiviral agent ('P-2', Polonine Development Lab., Woodside, NY) in treating BLV-positive cattle. The results of the trial were incon- clusive. A recent report by Sundquist and Oberg [13] indicates that the antiviral, phos- phonoformate, specifically inhibits bovine leukemia and related viral RNA polymerases. Several compounds are known to have a significant inhibitory effect on the development of C-type retroviruses and on the diseases induced by these viruses in laboratory animals. Among the more effective of these antiviral agents is 1-fl-D-ribofuranosyl-1,2,4-triazole- 0166 -3542/81/0000 -0000/$02.50 © Elsevier/North-Holland Biomedical Press